How is human memory affected by emotions?

Kristina Kleinova

How is Human Memory Affected by Emotions? Kristina Kleinova

Table of contents Abstract 2 .....................................................................................................................................

Introduction 2 ..............................................................................................................................

Human Memory 3 .......................................................................................................................Neuroanatomy of Memory 4 .........................................................................................................Neurones and Neural Transmission 5 .............................................................................................Memory Forma7on 6 ....................................................................................................................

Sensory Memory 6 ...........................................................................................................................Working Memory 7 ...........................................................................................................................Long-Term Memory 9 .......................................................................................................................

Recall and Recogni7on 11 ..............................................................................................................Forge=ng 11 .................................................................................................................................

Emotions 12 .................................................................................................................................Neuroanatomy of Emo7ons 12 ......................................................................................................Psychology of Emo7ons 13 ...........................................................................................................Neurobiology of Emo7ons 14 ........................................................................................................

The Interactions between Human Memory and Emotions 15 ................................................The Effect of Emo7ons on Declara7ve Memory 17 .........................................................................

Emo7ons and Encoding 17 ...............................................................................................................Emo7ons and Consolida7on 17 ........................................................................................................Emo7ons and Retrieval 19 ................................................................................................................The Effect of Emo7ons on Different Aspects of a Memory 20 .........................................................

Repressed Memories 22 ................................................................................................................Emo7onal Context and Memory 23 ...............................................................................................The Effect of Emo7ons on Non-Declara7ve Memory 23 .................................................................

Analysis 25 ...................................................................................................................................

Conclusion 26 ..............................................................................................................................

Bibliography 27...........................................................................................................................

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Abstract Human memory and emotions are two phenomena of the human brain that influence each other by a network of connections. In this report, these two functions of the brain are explained, and subsequently the effect of emotions on memory is being discussed in order to to find out various ways in which this interaction occurs. These effects can arise mainly from the interactions between the hippocampus, centre of long-term memory formation, and the amygdala, centre of emotions. Emotions can have both enhancing and impairing effect on memory which have been investigated through many studies and experiments with healthy people or those with damage to brain structures involved and often using functional magnetic resonance imaging. This report investigates and compares the impacts on different aspects of memory like separate processes involved, different features or types of a memory as well as the influences of emotional content and context.

Introduction ‘Everything in life is memory, save for the thin edge of the present’

cognitive neuroscientist Michel Gazzaniga 1

The effect that emotions have on human memory is a complex concept and can be investigated from many points of view. However, before it can be addressed, the principles of memory and emotions need to be fully explained.

Memory is undoubtedly a crucial part of our personality as well as survival. Over time, there have been many models of the way memory operates going back even to times of philosophers like Plato before the current model that contemporary scientists work with was constructed. If we were to define memory nowadays, it is the knowledge that is stored in the brain and the processes of acquiring, consolidating and retrieving such knowledge . Its primary function is to guide our actions in the 2

present according to information from our previous experience. There are many different subdivisions of memory according to various criteria, however, probably the most significant distinction is between short-term (working) and long-term memory. Short-term memories can be turned into long-term memories usually in the part of the brain called hippocampus by specific processes depending on many factors such as emotions.

Another phenomenon that affects the brain and body are emotions. These are, unlike what we usually consider them as, responses of the body to stimuli in order to either save us from danger or lead us to a reward. These are then often associated with conscious feelings whether negative or positive, however, much of the time we are unaware of them. A main center of these emotions in the brain is amygdala that has connections to large amount of other areas of the brain that process data from various receptors.

These two phenomena, memory and emotions, often interact and affect each other. Strong emotions can affect the processes of storing and retrieving of memories in either positive way, by increasing the probability of a memory to be stored as long-term, or negative way like repressed memories. There are three main aspects of memories that could be affected: the quantity of events remembered, the vividness (quality) of them and the accuracy of the information. Emotions can also influence 3

memory through two forms, emotional content or context, which can result in different effects on memory.

Jonathan K. Foster, Memory: A Very Short Introduction (New York, Oxford University Press Inc., 1

2009), p. 2

Daniel Tranel and Antonio R. Damasio,‘Neurobiological Foundations of Human Memory‘, in The 2

Handbook of Memory Disorders, ed. By A.D. Baddeley, M.D. Kopelman and B.A. Wilson (John Wiley & Sons, Ltd., 2002)

Elizabeth A. Kensinger and Daniel L. Schacter, ‘Memory and Emotion’, in Handbook of Emotion, 3

ed. By Michael Lewis, Jeannette M. Haviland-Jones and Lisa Feldman Barrett (New York, The Guilford Press, 2008)

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By using fMRI (functional magnetic resonance imaging) and studies with patients that suffered a damage to either amygdala or hippocampus or healthy patients using various emotional stimuli to induce the emotional effect . The cooperation of the systems has the main effect on the emotional component of memories often resulting in enhancement of the resulting stored information.

However, sometimes the result can be also be impaired due to strong negative emotions and reduce the amount and quality of stored memories. One of these cases is repression when memories are unconsciously pushed out due to their traumatic aspect. Another negative effect is that attention is diverted towards emotional information at the expense of non-emotional ones.

Human Memory Memory connects our past with present and therefore is part of our personality as well as facilitating our future decisions.. It is a term that covers more of different brain functions and it is the capacity to store information. The main purpose of memory is recreating information and experiences from our past to help us with present actions. This is enabled by synchronous firing of neurons that originally were used during the experience. 4

There are different types of memory that stored by various processes in separate places in the brain. These can be divided into categories according to different criteria. The main division is according to the length of time that the memory is retained in the mind. These subdivisions are sensory memory, short-term memory (also called working memory) and long-term memory. There has also been attempt of introduction of medium-term memories, however, these haven’t been widely accepted. These types are then subdivided depending on the content of the memory. Long-term memory is especially divided into non-declarative (implicit or procedural) memories and declarative (explicit) memories that have further sub-categories as could be seen in Figure 1.

! Figure 1: Classification of human memory 5

Carter, Rita, The Brain Book (London: Dorling Kindersley Limited, 2014), p. 1264

https://www.psychestudy.com/cognitive/memory/types (accessed on 28.11.2016)5

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Neuroanatomy of Memory The structure of the human brain is complicated and can be classified in many ways, however, the major component of the brain is the cerebrum that is divided into two hemispheres, left and right. The Cerebrum is also divided into four main lobes called frontal, parietal, temporal and occipital lobe. There is another larger part of brain called cerebellum or little brain and the medulla connected to the spinal cord. In the innermost parts of the brain there are smaller divisions such as putamen, mamillary body or thalamus. 6

! Figure 2: Main division of the human brain 7

We cannot exactly point out the location of memory in the brain, however, there are parts of the brain that have increased activity when memories are formed and places where memories are stored more densely. The most important part in turning experiences into memories and therefore forming long-term memories is played by hippocampus, without it a person is not able to form new long-term memories. This was the case of Henry Molaison (usually referred to as H.M.) a large part of whose hippocampus was removed to prevent him from having seizures due to his epilepsy. However, after the surgery he remembered everything from his past but he wasn’t able to form any new long-term memories. This meant that memories had to be stored in different places as we now know. Many 8

parts are involved in memory storing though some regions are more important than others. The frontal lobe is where working memory occurs and therefore shot-term memories are formed and is also important for decision making. The parietal lobe is involved in creating and storing of spatial memories that help us orientate in space, while the temporal lobe is mainly associated with general knowledge such as facts (semantic memory). The amygdala, located near the hippocampus, holds memories with strong emotional aspect and will be discussed later in this report. Further, the mammillary body holds episodic memories whereas the caudate nucleus and the putamen are involved with procedural and instinctive skills and therefore with non-declarative memories. 9

However, memory consists of many different aspects that are stored separately in different parts of the brain and when recalled they are put back together. Distribution of memories into different regions of brain not only ensures order of memories but also prevents losing of all memories when some part of brain is damaged

Carter, Rita, The Brain Book (London: Dorling Kindersley Limited, 2014), pp. 52-556

http://controlmind.info/human-brain/structure-of-the-brain [accessed on 28.11.2016]7

Swaab, Dick, We Are Our Brains: From the Womb to Alzheimer’s (London: The Penguin Books, 8

2015), p. 262

Ibid.9

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! Figure 3: Cross-section of the Brain to Show the Location of Hippocampus (blue) 10

Neurones and Neural Transmission Before talking about forming of memories, creation of nerve impulses and their transmission through synapses have to be explained. There are many types of brain cells that are in two major groups called neurones and glial cells. Neurons carry electro-chemical impulses while glial cells’ function is mainly physical support of neurones. There are billions of neurones in human brain that are all connected in a huge web by synapses between axons and dendrites.

Nerve signals consist of more discrete impulses also called action potentials. When there is no 11

transmission happening through axon of a neuron, it is in a state called resting potential. The neuron is polarized which is due to the difference in electrical potentials as a result of unequal distribution of positive ions inside and outside the axon. Sodium and potassium ions are maintained in inequality by active transport and facilitated diffusion. Ion channels in the cell membrane are leaky and so they allow some sodium ions (Na+) and to move in and potassium ions (K+) to move out even more as K+ ion channels are usually more ‘leaky’. These ions are transported across the membrane also by protein pumps called Na+K+ATPase that pumps two K+ in and three Na+ out and therefore causing inequality of ions. As soon as the impulse arrives, positive sodium ions move through the channels in the axon 12

membrane into the axon, so that the inside is now positive and outside negative. This is called depolarization. After the impulse leaves, repolarization happens. Positive sodium ions flow out of the axon while potassium ions rush inside and resting potential is restored. Eventually, this impulse reaches a synapse connecting two neurones where there is very narrow gap separating two membranes of neurones. Here the impulse is transferred thanks to neurotransmitter that is produced in the neurone cell and packed into vesicles called synaptic vesicles. When impulse arrives to presynaptic membrane, synaptic vesicles merge with the membrane and the neurotransmitter diffuses out of the cell to the post-synaptic membrane where receptors register it. Molecules of neurotransmitter bind to receptors 13

of membrane channels and these channels will open allowing positive ions to move inside the neuron causing depolarization and impulse can continue.

Unknown, ‘Long-Term Memory’, Psychestudy, https://www.psychestudy.com/cognitive/memory/10

long-term [last accessed on 11.12.2016]

Carter, Rita, The Brain Book (London: Dorling Kindersley Limited, 2014), p. 72-7311

Boyle M. & Senior K., Human Biology: Third edition (London: HarperCollinsPublishers, 2008), p.12

226

Carter, Rita, The Brain Book (London: Dorling Kindersley Limited, 2014), p. 72-7313

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Memory Formation Memory formation is composed of many different processes and these could be divided into three main steps: acquisition, consolidation and storage. Acquisition (or encoding) is the process of sensory information from receptors being brought to the brain and sensory memory structures and then passed to working memory. Consolidation is the process of rehearsing knowledge and building a representation of it in the brain. Storage is the last step and it involves creation of a relatively stable trace of this knowledge in the brain and therefore forming long-term memory. 14

Memory is a form of phenomenon called neural plasticity. Neurons can be altered differently as a response to different external stimuli. There is short-lasting and long-lasting plasticity. Short-term plasticity is caused by synaptic events such as the increased release of neurotransmitter and it only lasts for few seconds or minutes. Long-lasting plasticity is accompanied by protein synthesis, growth of neural processes and new synaptic link. 15

Further down, dual-store memory model will be described that was proposed by Atkinson-Shiffrin and is currently accepted between scientists even though there has been some evidence that contradicts this idea. 16

Sensory Memory Sensory memory (SM) is the ability to retain impressions of sensory information after the original stimuli have ended. It lasts only for about 200-500 milliseconds, however, has huge capacity for 17

stimuli as it constantly receives enormous amount of data from various receptors that are then either perceived or ignored. Existence of sensory memory can be proven by several simple tests of different stimuli. Though mainly experiments conducted by George Sperling prove the presence of such memory as well as allowed us to estimate its period of retention and capacity. This American cognitive psychologist mainly tested memory of visual information by presenting 12 letters in very briefly, only about 50 milliseconds, to participants. These participants could then recall only 3-4 18

letters, however, Sperling suspected that they could actually remember more but the information fade too rapidly and so he tested them more by changing the technique of recall. He then continued his research proving different aspects of sensory memory.

These aspects of sensory memory can be divided according to human senses. It is therefore separated into three main types: iconic, echoic and haptic memory. Iconic or visual memory involves information from the receptors in eyes and can be proven, for example, by looking at rotating wheel with glowing ember on it in a dark room, when it spins fast enough we can eventually see just glowing circle which means that there has to be some store of this visual information . Echoic 19

memory is store of auditory information from ears and allows us to, for example, detect the location of the source of the sound. The store of sense of touch is called haptic memory and it involves memory of experiencing pressure, pain or itching.

Daniel Tranel and Antonio R. Damasio,‘Neurobiological Foundations of Human Memory‘, The 14

Handbook of Memory Disorders, ed. By A.D. Baddeley, M.D. Kopelman and B.A. Wilson (John Wiley & Sons, Ltd., 2002), p.

Squire L.R. & Paller K.A., ‘Biology of Memory’, Comprehensive Textbook of Psychiatry 15

(Lippincott Williams & Wilkins, 2000)

Alan D. Baddeley, ‘The Psychology of Memory’, The Handbook of Memory Disorders, ed. By A.D. 16

Baddeley, M.D. Kopelman and B.A. Wilson (John Wiley & Sons, Ltd., 2002), p.

http://www.human-memory.net/types_sensory.html (accessed on 28.11.2016)17

Jonathan K. Foster, Memory: A Very Short Introduction (New York, Oxford University Press 18

Inc., 2009), p. 28

Alan Baddeley, ‘Sensory Memory’, in Essentials of Human Memory (Psychology Press, 1999)19

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Via a process called attention, which is the cognitive process of selectively concentrating on one aspect of the environment while ignoring other things , a fraction of the sensory information is 20

passed on to working memory and used further. The sensory information that we do not use is rapidly lost and is impossible to restore as it is outside our consciousness. You can imagine this decay as when light fades or sound dies out. 21

Working Memory Working memory is often referred to as short-term memory, however, these two names do not have exactly the same meaning. Short-term memory suggests a passive store of the information while working memory shows us the active nature of this type of memory. These are also closely related to 22

consciousness as it is essential what we currently ‘hold in our mind’. It is a temporary store of information that is needed to perform a response to stimulus at that moment. Currently we have sufficient evidence to prove that the working memory consists of multiple subsystems rather than one system. In the current model of working memory that was presented by A. D. Baddeley, it is said that there are four main systems involved, central executive, phonological loop, visuo-spatial sketchpad and episodic buffer. This division can be supported by studies involving fMRI that generally show 23

activity mainly in the dorsolateral prefrontal cortex when working memory is used but different areas are activated as well depending on the nature of the information. Visual and spatial type of stimuli caused activation of the right side while verbal type activated left side of the dorsolateral prefrontal cortex. Therefore, there must be individual systems dealing with different types of working memory. 24

The Central Executive is possibly the most essential component of the working memory as it acts as the directing centre. It doesn’t posses storing function but it controls the allocation of attention to different parts through focus, dividing and directing attention. It also connects other parts of 25

working memory and possibly ‘communicates’ with long-term memory. Another ability of the central executive is to allow new approaches and behaviour when previously learned ones are no longer reliable. This was supported by patients with damage to frontal lobe, which is thought to be the location of central executive, that had problem with creating new ways of solving problems and adapting to new behaviour. This condition is called ‘dysexecutive syndrome’ and it suggests that the central executive is responsible for this functions sometimes called executive functions. However, 26

the central executive is the least understood part as it was discovered relatively recently and is very complex making it difficult to investigate with current techniques.

Another component of working memory is phonological loop that is involved in speech and storage of auditory information. It has no capacity to perform decision-making or division of attention and therefore it is simply just a store of the information that has been heard and as well as being responsible for ‘inner speech’. It has two subcomponents called phonological store and articulatory

Mastin Luke, ’Sensory memory’, The Human Memory: What It Is, How It Works and How It Can 20

Go Wrong, http://www.human-memory.net/types_sensory.html [last accessed on 13.12.2016]

Jonathan K. Foster, Memory: A Very Short Introduc3on (New York, Oxford University Press 21

Inc., 2009), p. 28

Ibid. p. 3322

‘The Working Memory Model’, h_p://www.sagepub.com/sites/default/files/upm-binaries/23

42874_Henry.pdf [last accessed 12.12.2016] p. 4

Alan D. Baddeley, Michael D. Kopelman & Barbara A. Wilson, ‘The Neurobiological Founda7ons of 24

Human Memory’, The Handbook of Memory Disorders, ed. By A.D. Baddeley, M.D. Kopelman and B.A. Wilson (John Wiley & Sons, Ltd., 2002), p. 36

‘The Working Memory Model’, h_p://www.sagepub.com/sites/default/files/upm-binaries/25

42874_Henry.pdf [last accessed 12.12.2016], p. 30

Ibid. p. 2226

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rehearsal mechanism. Phonological store is ‘passive’ as it only holds speech and auditory material for limited periods of time as a memory trace and then it fades away by trace decay (process of memory dissipation). Articulatory rehearsal mechanism has two main functions. One of them is recitation of the information from the phonological store to prevent the trace decay as it is being constantly refreshed. This happens internally and there is a lot of disagreement about the way this is carried out. The other function is verbal encoding, a process when visual information is assigned a verbal label and therefore it is converted into phonological code, through articulation process, that is then temporarily stored in phonological store, however, this is optional.

The third aspect of working memory is visuo-spatial sketchpad that processes visual and spatial information. It is also considered as ‘passive’ as it only holds the information but doesn’t have the overall control. There has been a suggestion that there are individual subsystems within it but unfortunately sufficient amount of evidence has not been provided yet. These subsystems should deal with different types of information. The main two are visual, that is what we see, and spatial, where we see it, possibly there is also third type that involves sequences of actions in a kinaesthetic code. 27

These memories are also subjected to rapid decay unless rehearsed. Compared to phonological loop, there hasn’t been enough evidence collected to support the details of these collection of processes.

The last part is the episodic buffer that is the most recent addition to this working memory model. It is defined as a temporary storage system that is able to combine information from the loop, the sketchpad, long-term memory, or indeed from perceptual input, into unified and coherent episode. It 28

provides also extra capacity for short-term information even though relatively limited and it allows access to some of long-term memories. There hasn’t been sufficient research done and so we still know very little about this component.

! Figure 4: Working Memory Model (Baddeley and Hitch) 29

The working memory model that has just been presented is one of the different models that have been created over time. However, in the past decades this one has been accepted in the scientific community as the most supported by evidence and most precisely describing the processes involved even though there are still many aspects that require further research and support as they are still just hypothetic.

‘The Working Memory Model’, h_p://www.sagepub.com/sites/default/files/upm-binaries/27

42874_Henry.pdf [last accessed 12.12.2016], p. 16

ibid. p. 3428

h_p://www.slideshare.net/Snowfairy007/aqa-as-psychology-unit-1-memory [last accessed on 29

13.12.2016]

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Long-Term Memory As mentioned before, the ability to form memories is based on neural plasticity. The ability of neurones to change their shape, structure and connection to another neurones or add new connections (synapses). The process by which the memory is established is called long-term potentiation (LTP) and it is a special case of synaptic plasticity. This happens during consolidation stage of memory formation in the brain structure called hippocampus where the memories are processed before being stored in various places of the brain. The phenomenon of long-term potentiation was first discovered by T. Bliss and T. Lomo while researching the hippocampus of rabbits. They found out that high frequency electrical stimulation of connected areas resulted in the nerve cells responding more strongly than they had previously and it could last for days, weeks or even longer that suggest mechanism for long-term learning in hippocampus. LTP was than researched more by in vitro 30

experimenting on slices of living tissue from hippocampus in order to understand the processes involved in long-term potentiation. 31

Hippocampus is located in the medial temporal lobe and has three main subdivisions that are important in LTP: the dentate gyrus, CA3 and CA1. Each of these sections has different types of nerve cells. When an impulse enters hippocampus it first travels through granule cells in dentate gyrus that are connected to CA3 pyramidal cells. These are subsequently joined to CA1 pyramidal cells by the axons of CA3 cells called Schaffer collaterals. LTP has been mainly observed between the Schaffer collaterals and the dendritic synapses of CA1 pyramidal cells. The pivotal roles in LTP are played by neurotransmitter glutamate, NMDA (N-methyl-D-aspartate) receptors and AMPA receptors. NMDA and AMPA receptors are embedded in the cell membrane of the postsynaptic cell (CA1). When an impulse reaches the synapse at the end of the Shaffer collateral, it releases the neurotransmitter glutamate. The amount of the glutamate released depends on the frequency of the impulse, higher the frequency the more glutamate secretion. Glutamate then binds to NMDA and AMPA receptors and opens them. The AMPA receptor is also permeable to Na+ ions and there will be an influx of them into the cell. NMDA receptors are permeable to both Na+ and Ca2+ ions, however, normally they are blocked by magnesium ion (Mg2+) that therefore prevents Ca2+ ions from entering the postsynaptic cell. When low frequency action potential reaches the synapse, a small amount of glutamate is secreted that will bind to receptors and cause sodium ions to enter the CA1 cell through the AMPA receptor. The NMDA will be still blocked by magnesium ion disabling calcium ions to enter and therefore no change other than propagation of action potential will occur. However, in case of high frequency impulse reaching the synapse, greater amount of glutamate is released and so more receptors will be stimulated to open resulting in greater number of Na+ ions passing through to the postsynaptic cell. This forms strong positive potential inside (depolarization) and repels Mg2+ ions out unblocking NMDA receptors due to electrostatic repulsion. Unblocked NMDA receptors, known as coincidence detectors, allow sodium and especially calcium ions to enter the cell. In terms of LTP, these calcium ions are essential as they act as secondary messengers that activate a cascade of intracellular processes in further two phases: early and late phase. , Calcium ion combines with 32 33

calmodulin and forms a complex that activates protein kinases. One of these kinases is CAM kinase (or CaMKII) that can affect AMPA receptors. In early phase, it initiates phosphorylation of these receptors and therefore increasing their conductance or it can promote movement of the AMPA receptors from the intracellular stores to the cell membrane and so increasing the number of available receptors. Ca+ ions can also act as retrograde messengers and allow more neurotransmitter such as nitric oxide to be released from the presynaptic cell. In late phase, the prolonged increased calcium

Terje Lomo, ‘The Discovery of Long-Term Poten7a7on’, Phil. Trans. R. Soc. Lond., Vol. 358 30

(2003online), pp. 617-620

D. Purves, G.J. Augus7ne, D. Fitzpatrick, et al, ‘Long-Term Synap7c Poten7a7on’, Neuroscience: 2nd 31

edi3on (Sinauer Associates, 2001)

Carleton University, ‘Neuroscience - Long-Term Poten7a7on’ h_ps://www.youtube.com/watch?32

v=vso9jgfpI_c&app=desktop [last accessed on 13.12.2016]

‘The Cogni7ve Neuroscience of Memory’, h_p://www.inference.phy.cam.ac.uk/jmb86/33

memory.pdf [last accessed on 14.12.2016]

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levels causes rise in the amount of transcription factors culminating in gene expression and so new proteins can be synthesised via protein synthesis. Some of these proteins are AMPA receptors that will be added to the membrane. However, there are also proteins synthesised that will promote growth of new synapses in the area of the original impulse. All of these modifications of the synapse result in higher probability of an action potential being transmitted and so allowing also lower frequency stimuli to be promoted next time.

! Figure 5: Long-term potentiation at a synapse 34

There are several types of long-term potentiation, the one presented above is NMDA-dependent hippocampal LTP that has been researched and understood the most. LTP has been observed in other parts of the brain like cerebral cortex, cerebellum or amygdala and so it can also happen between different types of neurones and can be distinguished by the receptor dependence. Different types of LTP may involve metabotropic glutamate receptor(mGluR) or other molecules instead of NMDA, however, the mechanism is basically same. Another criteria according to which LTP can be divided is pre- and post-synaptic activity. These subdivisions are Hebbian, non-Hebbian and anti-Hebbian LTP that are named after Donald Hebb that stated the basic principle behind memory formation: “When an axon A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased.” 35

Long-term memory can be divided into declarative (explicit) and non-declarative (implicit) memory. Declarative memory includes factual memory and memories of experiences that can be ‘brought to mind’ and consciously recollected. These memories are mainly involved in hippocampal processes. Non-declarative memory involves skills, habits and forms of conditioning and priming and they are usually not included in the hippocampal system or mesial temporal lobes. An evidence for this distinction is that different parts of the brain show activity on fMRI scans when different types of memories are involved and people with damage to a certain part of the brain and that suffered a loss of explicit memories still retain implicit memories. This means that there are also different processes 36

involved especially various types of LTP though these vary even within one subdivision of long-term

h_p://bigtone.zone/2013/12/05/long-term-poten7a7on-depression/ (accessed on 28.11.2016)34

Donald O. Hebb, Organiza3on of Behavior: a Neuropsychological Theory (New York: John Wiley, 35

1949)

Alan D. Baddeley, Michael D. Kopelman & Barbara A. Wilson, ‘The Neurobiological Founda7ons of 36

Human Memory’, The Handbook of Memory Disorders, ed. By A.D. Baddeley, M.D. Kopelman and B.A. Wilson (John Wiley & Sons, Ltd., 2002), p. 28

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memory and therefore it is difficult to determine with certainty what process is involved in storing of a certain memory. However, we can see some trends such as the ones that were mentioned before. Recall and Recognition Recall and recognition are two main ways of retrieving memories. Recall is the conscious reforming of the information acquired in the past that was previously encoded and stored in the brain. Recognition is the unconscious process of association of an event or an object with previously experienced or encountered one. The regions that show increase activity on PET and fMRI scans are 37

the prefrontal cortex, hippocampal and parahippocampal regions, the anterior cingulate cortex, the cerebellum and a few other parts. Recognition is often considered as superior as it only involves 38

familiarity decision while recall process consists of two stages. Recognition requires only decision about whether a certain thing has been encountered before and therefore recognition is often what triggers recall as it activates a certain neural network that will subsequently cause the activation of entire network and results in recall. Recall is basically a reconstruction of various aspects of a memory that are scattered in various parts of the brain and are connected by a network of neurones that was formed during formation of the memory. During this process, several neural pathways have to be triggered by stimuli to activate this reconstruction and eventually returning of the memory from long-term storage to working memory. This can happen either through direct retrieval, when memories are linked directly, or hierarchal inference, when a certain information is linked to several subsets of facts. Scientists have two main theories to describe the recall processes: The Austin Simonson theory and the theory of encoding specifity. The Austin Simonson theory says that recall starts with a search and retrieval process, and then a decision or recognition process where the correct information is chosen from what has been retrieved. The encoding specifity principle highlights the 39

similarities between recall and recognition and believes that if information that was present at encoding is also present when retrieved, the retrieved memory is enhanced. There are three types of recall: free recall, cued recall and serial recall. This division is according to the order in which memories are retrieved. Another fact about recall that will be significant later is that it is state-dependent which means that memories are retrieved more easily when individuals are in the same state, whether emotional or under the influence of alcohol or drugs, as when memory was encoded.

Forgetting Forgetting is a inevitable process of loss or modification of long-term memories and therefore making it impossible for the information to be recalled. It allows for new memories to substitute the old ones or the old ones being adjusted due to new experience that will perfect the knowledge for future purposes. Many factors affect forgetting such as time period for which memory has been stored. There are four main theories behind forgetting: context-dependent forgetting, interference theory, organic causes and decay theory. Context-dependent forgetting refers to the cause of unsuccessful retrieval being missing stimuli that was present during encoding and so recall cannot be triggered even though this memory is not completely lost. Interference theory states that acquisition of new information 40

causes forgetting of the older ones as a result of the competition between these two. This means that these get confused or combined and will result in distorted memories. Organic causes are referred to 41

as the loss of memories due to damage to parts of the brain either as result of injury or a disease such as Alzheimer’s disease. Decay theory believes that the neurochemical and physical change due to memory decays (fades away) over time when it is not used at least sometimes and so the connections become weaker. These theories each explain some phenomena, however there is evidence that

h_p://www.human-memory.net/processes_recall.html (accessed on 28.11.2016)37

‘The Cogni7ve Neuroscience of Memory’, h_p://www.inference.phy.cam.ac.uk/jmb86/38

memory.pdf [last accessed on 14.12.2016]

E. Tulving & M. Thompson, ‘Encoding specificity and retrieval processes in episodic memory’, 39

Psychological Review, Vol. 80 No. 5 (1973)

C. Flanagan, D. Berry, M. Jarvis & R. Liddle, ‘Explana7ons for Forgeqng’, AQA Psychology for A-40

Level Year 1 & AS (Illuminate Publishing, 2015), p. 54-57

Ibid.41

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contradicts some aspects a therefore that is why there are just theories and cannot be considered as the true mechanism behind forgetting.

Emotions Human emotions are usually temporary changes in the human body as a result of the response to stimuli. It could be said that they have three separate components: a subjective experience, a physiological response and an expressive response. They are crucial for people’s survival as they 42

prompt the action to either get away from danger or lead to a ‘reward’. Emotions can result in 43

conscious pleasant or unpleasant feelings, however, the emotional reaction of the body happens unconsciously so that its reaction is rapid and therefore gives survival advantage. Emotion is transient and arises as a response to immediate stimuli while if it lasts for longer time period we call it mood. The structures of the body that are the most significant for emotions are the limbic system and autonomic nervous system.

Neuroanatomy of Emotions The limbic system is a group of several brain structures located deep in the brain. It consists of thalamus, hypothalamus, hippocampus and amygdala. It is greatly involved in the emotional life and also long-term memory formation. The thalamus is the primary relay station for sensory information incoming from the rest of the body. The hypothalamus is mainly controlling homeostasis but it also regulates hunger and thirst, response to pain, pleasure and sexual satisfaction, anger and others. In 44

order to regulate all of these, it has to possess the ability to regulate the autonomic nervous system as well as the pituitary gland that performs hormonal regulation. The hippocampus has been previously mentioned as the centre of long-term formation. The amygdala is probably the most crucial part for processing of emotional stimuli as it acts as the controlling centre for behaviour, emotional responses and emotional memory. It has great survival importance as it regulates stress response. This function of the amygdala has been proved by the stimulation of the area in an animal brain resulting in aggressive response. Another evidence is that individuals with lesions (damage) on amygdala have a reduction in stress and other emotional responses. The amygdala has large amount of connections with many other brain regions from which it receives sensory information that will result in an emotional reaction. Its main function is therefore to process and translate the sensory data to generate appropriate reactions. Sometimes the cortex is included as part of the limbic system dealing with mood, judgement and motivation. It has several subunits such as the cingulate cortex or the olfactory complex. Frontal cortex is also important in processing of emotions as it receives information from the limbic system and produces conscious feelings. The autonomic nervous system is a part of the peripheral nervous system that is outside our conscious control and it regulates primary functions of the human body such as heart rate. It divides into two systems: sympathetic and parasympathetic nervous system (NS). The action of the Sympathetic NS results in increase of the rate of functions in the body and prepares it for a response while parasympathetic NS decreases them back to normal when body is at rest.

Kendra Cherry, ‘What Are Emo7ons and the Types of Emo7onal Responses’, Very Well, h_ps://42

www.verywell.com/theories-of-emo7on-2795717 [last accessed on 13.12.2016]

Carter, Rita, The Brain Book (London: Dorling Kindersley Limited, 2014), p. 12643

George Boeree, ‘The Emo7onal Nervous System’, h_p://webspace.ship.edu/cgboer/44

limbicsystem.html (accessed on 1.12.2016)

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! Figure 6: The anatomy of the limbic system and the pathways various sensory information take to arrive at the

amygdala 45

Psychology of Emotions Psychologists identify ten basic emotions: joy, contempt, surprise, shame, sadness, fear, anger, guilt, disgust and interest. It is believed that other emotions are simply just combinations of these as ‘the 46

wheel of emotions’ proposed by Robert Plutchnik demonstrates. The psychological description of 47

the emotions is the two-dimensional model. This model classifies emotions according to two criteria, valence and arousal. Valence refers to whether the emotion is negative or positive. Arousal depends on the excitement meaning that events causing high arousal emotions are exciting and vice versa.

! Figure 7: Two-dimensional model of Emotions 48

Many theories have been introduced to explain questions concerning emotions. These theories can be classified into three groups: physiological, neurological and cognitive. Though probably the most essential theory is the evolutionary theory of emotion proposed by Charles Darwin that explains the

h_p://webspace.ship.edu/cgboer/limbicsystem.html [last accessed on 14.12.2016]45

CrashCourse, ‘Emo7on, Stress and Health’ h_ps://www.youtube.com/watch?v=4KbSRXP0wik [last 46

accessed on 14.12.2016]

Kendra Cherry, ‘What Are Emo7ons and the Types of Emo7onal Responses’, Very Well, h_ps://47

www.verywell.com/theories-of-emo7on-2795717 [last accessed on 13.12.2016]

h_ps://www.computer.org/csdl/trans/tp/2008/12/_p2008122067.html (accessed on 12.12.2016)48

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purpose of emotions as they have an adaptive role. Emotions allow rapid responses to environment 49

and increase chances of survival. Understanding others’ emotions plays an essential role for individual’s success. Physiological theories, for example the James-Lange theory, believe that emotions are the result of responses within the body. The neurological ones suggest that the activity in the brain leads to emotional responses. The cognitive theories say that the basis of forming emotions 50

are our thoughts and other mental activity, an example of this is Schachter-Singer two-factor theory. All of these theories contribute to overall explanation of emotions and shape the system behind the emotions which is an evaluative system that determines a given situation is potentially harmful or beneficial to the individual. It is therefore unconscious process, however, it can result in conscious emotional experience.

Neurobiology of Emotions The main processor behind emotional expression is the amygdala. When an external stimulus is registered at the location of receptors it is transmitted to the appropriate brain structure, a sensory cortex in the prefrontal or temporal lobe that is connected to corresponding part of the thalamus. Thalamus then ‘passes’ the information to the amygdala that receives large amount of inputs from various thalamic and cortical systems. These inputs have various intensities and levels of representation and depending on that they are processed in different parts of the amygdala. The amygdala consequently sends out signals to various parts of the brain to generate an emotional response by behavioural responses, autonomic system responses or endocrine responses. This can 51

trigger physiological changes like increased heart rate or increase in neurotransmitter levels and hormonal levels. Different emotions will activate different emotional circuits to generate response. The emotional stimulus triggers two routes, one is this unconscious and primary response and the second one results in conscious awareness of the emotion, feeling. This is more accurate and slower pathway that involves the sensory information going back, as it is reversible relationship, to the frontal cortex where the emotion is expressed as conscious feeling that we actively think about and realize. The cortex can receive also direct emotional stimuli as well as information from the hippocampal-dependent memory store relevant to the situation. All of these contribute to the formation of feeling. This process is related to the working memory. To be more precise, it allows the emotional experience to be kept in the awareness and used in thinking and decision making as it is temporary stored. 52

Kendra Cherry, ‘Theories of Emo7ons’, Very Well, h_ps://www.verywell.com/theories-of-49

emo7on-2795717 [last accessed on 13.12.2016]

Kendra Cherry, ‘Theories of Emo7ons’, Very Well, h_ps://www.verywell.com/theories-of-50

emo7on-2795717 [last accessed on 13.12.2016]

Fellous Jean-Marc, Armony Jorge L. & LeDoux Joseph E., ‘Emo7onal Circuits and Computa7onal 51

Neuroscience’, The Handbook of Brain Theory and Neural Networks (2002), p. 2

LeDoux Joseph E.,’ Emo7on Circuits in the Brain’, Annual Review in Neuroscience, Vol. 23 52

(2000), p. 176

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! Figure 8: The sequence of actions that lead to emotional response and conscious feeling 53

All of these processes and circuits are regulated by neurotransmitters via the monoamine systems. 54

These systems are the dopamine, the serotonin and the noradrenaline (norepinephrine) system. Various emotions are essentially a result of different combinations of the levels of these three chemicals being produced and released as part of emotional response. All of the neurotransmitters are monoamine neurotransmitters which means that they contain a single amine group. Dopamine can be both inhibitory and excitatory neurotransmitter depending on the receptors present. It is involved in focus, clear thinking, libido and alertness. High levels of dopamine usually result in the improvement of mood and attention. Dopamine is synthesised in the brain and it cannot leave to the rest of the body. Noradrenaline can be derived from dopamine and it is mainly excitatory neurotransmitter. Unlike dopamine, noradrenaline is capable of moving around the body and affects mainly sympathetic nervous system. Serotonin is both excitatory and inhibitory neurotransmitter that is involved in regulation of mood, aggression, appetite and sleep as well as certain cognitive functions of the brain. Low levels of serotonin can result in disruption in sleep-wake cycle, depression or anxiety disorders and therefore it is often used in anti-depressants. On the other hand, high level of serotonin causes relaxation, apathy and eating disorders.

Though, it is important to note that these chemicals do not cause the emotions, they merely contribute to the emotional reaction as being one of the components of the mechanism. They either excite or inhibit certain synapses that contain receptors for these neurotransmitters that will result in either higher or lower probability of an action potential to be transmitted. These types of synapses are in the emotional circuits and therefore if the amount of excitatory neurotransmitter is increased a certain emotional circuit is more likely to be activated culminating in the emotional response and conscious feeling.

The concept of emotions is still being thoroughly researched as it is a complex set of events and processes that has not been fully understood yet. This means that there are still many areas of the topic that we are unable to explain especially when it comes to more complicated emotional responses as opposed to fear response which has been researched the most as it is fairly simple. Therefore, we still cannot determine with full certainty the functioning of emotions even though there are many theories that give us good idea of what is happening.

The Interactions between Human Memory and Emotions

h_p://www.nature.com/nrn/journal/v5/n7/fig_tab/nrn1432_F2.html (accessed on 12.12.2016) 53

‘The Neurobiology of Emo7on: Neural Systems, the Amygdala and Fear’, h_p://54

www.neuroanatomy.wisc.edu/coursebook/neuro5(2).pdf [last accessed on 13.12.2016]

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Human memory can be affected by many factors and one significant factor is emotion. The fact that they must influence each other can be seen from the location of the brain structures mainly involved in memory formation and emotions. The hippocampus and the amygdala are both parts of the limbic system and are located next to each other. It is therefore logical to say that there must be certain cooperation between these two structures of the brain.

These two systems, hippocampus and amygdala, operate relatively separately until a memory meets emotion. In this case, these two regions are both activated and especially the connections between 55

them show activity. This relationship is known to be bi-directional as emotions not only affect memories but memories can also affect the emotional response. The evidence for this cooperation 56

between the hippocampus and amygdala comes from studies using fMRI scans. In these investigations people with different degrees of damage to amygdala and hippocampus were involved and studied as well as people with no lesions on these structures. The results showed that people subjected to stimuli that had emotional component had more activity detected in the amygdala than when introduced to neutral stimuli that caused only low or no activity in the amygdala. Another finding was that participants with amygdala pathology showed almost no difference between remembering neutral or emotional information. The ability to remember neutral cues was also only affected by damage to hippocampus but not to amygdala. , All of this evidence supports the effect of emotions and the 57 58

amygdala on memory.

! Figure 9: Scans of the brain showing activity of the amygdala (blue) and the hippocampus (yellow) 59

The amygdala affects mainly hippocampal-dependent emotions as these are usually episodic memories and therefore have emotional aspect to them. It is well known that people tend to remember

Elizabeth A. Phelps, ‘Human Emo7on and Memory: Interac7ons of the Amygdala and Hippocampal 55

complex’, Current Opinion in Neurobiology, Vol. 14 (2004), pp. 198-202, p. 201

ibid, p. 200 56

M.P. Richardson, B.A. Strange & Dolan R.J. , ‘Encoding of Emo7onal Memories Depends on the 57

Amygdala and Hippocampus and Their Interac7ons’, Nat Neuroscience, Vol. 7, No. 3 (2004), pp. 278-285, p.278

Elizabeth A. Phelps, ‘Human Emo7on and Memory: Interac7ons of the Amygdala and Hippocampal 58

complex’, Current Opinion in Neurobiology, Vol. 14 (2004), pp. 198-202, p. 200

h_p://scan.oxfordjournals.org/content/early/2011/05/06/scan.nsr027/F1.expansion.html [last 59

accessed on 12.12.2016]

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more experiences that involved a strong emotion whether positive or negative. However, it can also affect non-declarative emotions which has mainly survival function so that the individual is able to react to dangerous or rewarding situations in more appropriate and rapid ways next time.

The Effect of Emotions on Declarative Memory The impact of emotions on declarative memory can be assessed in several ways as the formation of them is a complex system that is currently relatively well understood and it is easier to investigate compared to the impact of emotions on non-declarative memories. First we can investigate the effect on separate stages of the formation of a long-term declarative memory that mainly occurs in hippocampus. Another way to study this effect is to look at different features of memory.

Emotions and Encoding Encoding is the process in which the stimulus is met for the first time and the primary factor that affects how is the stimulus encoded is attention. The emotion can influence the attention by changing focus onto the emotional stimuli and therefore making their processing easier. To demonstrate this, a 60

paradigm called attentional blink would be used. In this paradigm, participants are subjected to two target stimuli in sequence of rapidly moving stimuli. Normally, the second stimuli would be missed, however, if it is an arousal stimulus, there was higher probability that it will be registered. However, if the amygdala is impaired also this attentional blink effect is affected and therefore the amygdala facilitates this effect. As the fMRI scans have shown, the main reason for this ability of the 61

amygdala is due to the huge number of connections to the sensory brain structures. The amygdala receives the emotional information before awareness and then through reciprocal connections can enhance the attention on the emotional stimulus also enhancing its encoding. It is difficult to 62

determine whether this influence of emotions on memory encoding is overall enhancing or impairing. It has enhancing effect on the memories with emotional content, however, it diverts attention from the other stimuli that can be missed or their encoding is impaired. In further studies of memory-emotion relationship, it also poses a problem because we cannot distinguish whether a certain emotional memory was remembered better due to the enhanced consolidation and recall or due to increased attention.

Emotions and Consolidation During consolidation, the encoded information is being processed in hippocampus which makes it fragile and prone to disruption. It usually also takes a long period of time and there has been suggestion that one of the reasons is to allow the emotional reaction to an event influence the storage of the event. There have been again many studies carried out to investigate mainly effect of 63

emotional arousal on the consolidation and subsequent storing of long-term memories. The results of these indicated three main points. The first one is that long-term memories of arousal events are enhanced but not short-term memories. Next, arousal rather than valence of the emotions is essential for consolidation. The last one states that the retention of the memory afterwards is positively

Phelps Elizabeth A., ‘Human Emo7on and Memory: Interac7ons of the Amygdala and Hippocampal 60

complex’, Current Opinion in Neurobiology, Vol. 14 (2004), p. 198

Phelps Elizabeth A., ‘Human Emo7on and Memory: Interac7ons of the Amygdala and Hippocampal 61

complex’, Current Opinion in Neurobiology, Vol. 14 (2004) p.198-199

Ibid.62

Ibid. 63

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correlated with the degree of arousal in the encoding. Another evidence supporting the enhancing 64

effect of the arousal is phenomenon called ‘flashbulb memories’. These memories usually involve some shocking event or surprising information that contains remarkable amount of detail and vividness and is encoded and stored at one occasion and retained for a lifetime. All of these therefore supports the notion that emotional information and emotionally arousing event are enhanced.

There have been many theories about how this enhancement occurs and what mechanisms are responsible. Research has implicated that the stress hormones released during arousing emotional response may have a key role in the processes. Findings of various functions and parts of the amygdala gradually supported the idea that amygdala has the crucial role in modulation of consolidation of long-term memory. Further investigations of the amygdala during consolidation showed that the basal nucleus (BA), part of the amygdala, is the main structure involved in the neuromodulatory mechanisms. This points to a certain interaction between the basal nucleus and 65

stress hormones during arousal. The only issue with these results was that they were mostly carried out on animals rather than on humans and so more results were needed to prove that humans have similar systems to the animals. This proof was provided by a study (Cahill, 1994) during which the individuals involved were given propranolol (β-adrenergic receptor antagonist) that resulted in the significant impairment of their memory of emotionally arousal experiences while it did not affect the neutral ones. , Therefore, the human consolidation of emotional memories is modulated by the 66 67

basal nucleus and stress hormones.

When an individual is subjected to threatening, exciting, surprising stimuli (arousal) or stressor conditions, in the body, stress hormones will be released as a part of the emotional response. These hormones divide into two groups, catecholamine hormones (epinephrine and norepinephrine) and glucocorticoids (cortisol). Catecholamine hormones can also act as neurotransmitters (norepinephrine) and are released from the adrenal glands or certain regions of the brain. Epinephrine is released in the body during stress response and causes several physiological changes. It also triggers the release of norepinephrine in the amygdala (more specifically basal nucleus) which is synthesised directly in the neurones of locus coeruleus and carried through the axons by monoamine transporters. Norepinephrine (NE) is then released into the synaptic cleft when the action potential arrives at the synapse. Norepinephrine molecules bind to the adrenergic receptors at the pre-synaptic and post-synaptic membrane. There are many adrenergic receptors that differ in the way they act when NE binds to them. Glucocorticoids (cortisol) are released by adrenal glands and are considered as ‘second wave’ of the emotional response. They have similar effect as epinephrine except that glucocorticoids 68

can pass into the brain and trigger the NE release directly.

Vlachos, Jannis, ‘The Influence of Emo7onal Arousal on Memory Consolida7on – a Connec7onist 64

Approach’, h_p://www.phil.uu.nl/preprints/ckiscrip7es/SCRIPTIES/051_vlachos.pdf [last accessed on 13.12.2016]

Ibid.65

Vlachos, Jannis, ‘The Influence of Emo7onal Arousal on Memory Consolida7on – a Connec7onist 66

Approach’, h_p://www.phil.uu.nl/preprints/ckiscrip7es/SCRIPTIES/051_vlachos.pdf [last accessed on 13.12.2016]

Jaf Darun, ‘The Role of the Amygdala in Emo7on and Memory’, h_p://www.diva-portal.org/67

smash/get/diva2:423629/FULLTEXT02 [last accessed on 13.12.2016]

Jannis Vlachos, ‘The influence of emo7onal arousal on memory consolida7on – a connec7onist 68

approach’, h_p://www.phil.uu.nl/preprints/ckiscrip7es/SCRIPTIES/051_vlachos.pdf [accessed on 12.12.2016]

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! Figure 10: The release of stress hormones in human body and their subsequent effect in the basal nucleus and

hippocampus 69

The most significant location of the NE action for the memory enhancement is in the hippocampus especially in the CA1 and dentate gyrus regions. In these areas, norepinephrine can induce long-term potentiation and therefore work with synaptic plasticity. The NE molecules bind to the adrenergic receptors (β-adrenergic or α-adrenergic) and can stimulate the hippocampal cells. By phosphorylating (binding to) these receptors, extracellular signal-regulated MAP kinase (EKR) and also other types of kinases will be activated that will promote long-term potentiation as described previously. There are 70

still unknown mechanisms underlying the whole system to be found and these are being currently researched. However, we could conclude that the arousal emotional events are more likely to be remembered as the stress response accompanying will result in enhancement of the long-term potentiation in the hippocampus which is the key process of forming long-term memories.

It is important to note, that this process does not always result in enhancement of the emotional memory consolidation. The difference lies between the amount of cortisol released during the stress response. When the level of cortisol is low to medium it usually facilitates consolidation while high level results in impairment of the process. There are two types of stress: acute and chronic. The acute one is immediate and is paired with lower levels of cortisol while the chronic one is caused by stressor for a long time and is often indicated by high levels of cortisol. This means that acute stress 71

enhances the process of memory consolidation and storing while chronic stress impairs it. This impairment is mainly expressed during memory retrieval as the high cortisol cause it to be less efficient and so harder to retrieve. Emotions and Retrieval Recall of memories with emotional content is mainly affected by the emotional state of the individual during the retrieval. To clarify, there is higher probability of recalling a memory when the emotional state of the individual during recall matches the emotional content or state during encoding of this information. There are two similar phenomena underlying this: the mood congruence effect and mood-state dependent retrieval. The mood congruence effect is the increased probability of recalling a

Jannis Vlachos, ‘The influence of emo7onal arousal on memory consolida7on – a connec7onist 69

approach’, h_p://www.phil.uu.nl/preprints/ckiscrip7es/SCRIPTIES/051_vlachos.pdf [accessed on 12.12.2016]

Keith Tully & Vadim Y. Bolshakov, ‘Emo7onal Enhancement of Memory: How Norepinephrine 70

Enables Synap7c Plas7city’, Molecular Brain (2010)

Renato Pasquali,’The Biological Balance between Psychological Well-Being and Distress: A 71

Clinician's Point of View’, Psychotherapy and Psychosoma3cs, Vol. 75, No. 2 (2006), p. 69

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memory that has the same or similar emotional content as the emotional state of the individual during the recall. This can be exemplified by the fact that we tend to recall memories with sad emotional content when we are feeling down. The mood-state dependent retrieval is a form of state-dependent memory effect and it concerns the increased effectivity of memory retrieval when the emotional state of the person during recall matches the state during encoding. For example, you are more likely to 72

recall a joyful memory when you are feeling happy. However, several studies have also shown that arousal emotions can have an impairing effect on retrieval unlike on consolidation. This occurs when glucocorticoid levels are still elevated during process of retrieval then they interfere with it making recall less likely to happen. 73

The Effect of Emotions on Different Aspects of a Memory The effects of the emotions on memory could be divided into three aspects: the quantity of the remembered information, the subjective vividness (quality) of memories and the amount accurate detail. We could also distinguish between negative and positive emotions and whether they have 74

different impact on memory.

The Effect of Emotions on the Quantity of Remembered information There has been number of investigations studying this phenomenon in order to gain evidence supporting the effect as well as comparing between different valence (whether it is positive or negative) of the memories. The individuals in the investigations were subjected to different emotional stimuli in a form words, sentences, pictures or narrated slide shows. It was important for the stimuli 75

with different valence to be as similar as possible in terms of general content, colour and sound intensities or other aspects to ensure that the results are mainly due to the change of valence. The participants generally were supposed to remember the cues showed and then asked to recall them later. Different studies worked with various types of cues that gave inconsistent results when comparing valence of the emotional stimuli. In the studies involving verbal and pictorial stimuli it was shown that there was a higher probability for negative stimuli to be recalled rather than the positive ones. While in a different investigation autobiographical experiences and information were assessed showing that memories with positive emotional content were more likely to be recalled than the negative ones. These contradicting results show that changing the valence of the stimuli doesn’t 76

have a specific effect on the memory. It could be explained by the fact that memory processes have evolved to store and then retrieve information that is most relevant to our goals whether positive or negative. Further studies were carried out to investigate the mechanisms behind these processes 77

using fMRI scans. The studies showed that successful encoding and retrieval of emotional information was accompanied by the greatest activity in the amygdala region. The difference in amygdala activity was also investigated in relation to valence of information as the amygdala is often said to be more involved with processing of negative emotions, however, when investigating

Tony W. Buchanan, ‘Retrieval of Emo7onal Memories’, Psychol Bull., Vol. 133, No. 5 (2007), pp. 72

761-779

D.J.F. Quervain, A. Aerni, G. Shelling & B. Roozendaal , ‘Glucocor7coids and the regula7on of 73

memory in health and disease’, Fron3ers in Neuroendocrinology, Vol. 30, No. 3 (2009), pp. 358-370

Elizabeth A. Kensinger & Daniel L. Schacter, ‘Memory and Emo7on’, Handbook of Emo3ons (2008), 74

p. 601

Elizabeth A. Kensinger & Daniel L. Schacter, ‘Memory and Emo7on’, Handbook of Emo3ons (2008), 75

p. 602

Ibid.76

Elizabeth A. Kensinger & Daniel L. Schacter, ‘Memory and Emo7on’, Handbook of Emo3ons (2008), 77

p. 603

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influence of negative or positive emotions on memory, amygdala showed equal activity in both cases. This also raised questions about whether the arousal is possibly causing the discrepancies. 78

Overall, these studies demonstrate that emotional events are more likely to be remembered rather than the neutral ones and so amygdala that mediates these helps to increase the quantity of information encoded and subsequently recalled. There is no clear evidence that would distinguish effect of the valence of stimuli on memory as it varies depending on the content.

The Effect of Emotions on the Quality of Remembered Information The quantitative assessments began the investigations of memory-emotion interactions. However, there is other aspect of memories that can be affect and that is their vividness. Some memories of the events can be so detailed that it seems as though the experience is being re-lived while other ones are blurry and we know it happened but lack more detail. Often the increased vividness of a memory indicates an emotional memory. The extreme form of this are ‘flashbulb memories’. The impact of 79

emotions was investigated in terms of arousal and valence. The arousal of an emotion impacts the quality as predicted and that is mainly by enhancing the quality of the memory. According to studies, different valence of an emotional stimuli has an impact on the quality of the memory as compared to quantity. Data from laboratory environment, where participants were supposed to remember information with different valence, show that generally the negative experiences are remembered more vividly than those that have positive emotional content. This connects to the idea that people in 80

positive mood often make more errors during reconstruction as opposed to those in negative mood. However, studies focusing on autobiographical memory, in which individuals were supposed to recall their own experiences, discovered that valence has an opposite effect. Though it has been argued 81

that it is due to the intensity of the emotion rather than valence as there is wide range of aspects of a real-life experience that may influence the intensity and so it is difficult to make them comparable. These effects were also studied with the aid of fMRI and it was found that the increased probability of increased vividness correlates with increased amygdala activity and interactions between hippocampus and amygdala.

To summarize, both high arousing and positive or negative emotions generally increase the quality of memory. In laboratory experiments, therefore in a way more comparable conditions, it was shown that negative events are remembered with greater vividness rather than positive ones. However, often in real life this is different as it greatly depends on intensity and subjectivity.

The Effect of Emotions on Accuracy of Detail of Remembered Information Emotions may increase the probability of increased amount and vividness of information but this can cause distortion of the accuracy and amount of detail. This is because emotion allows enhancement of the general theme of the event while it reduces the amount of specific detail of the memory. It means 82

that emotions only enhance part of the encoding episode and so not all details are accurately encoded. The theory explaining this is that the emotion increases the likelihood of remembering the emotional detail (intrinsic) of the event while not enhancing the non-emotional (extrinsic) details of it. For 83

example, individuals were more likely to remember neutral words that were as a part of a sentence

Ibid.78

Elizabeth A. Kensinger & Daniel L. Schacter, ‘Memory and Emo7on’, Handbook of Emo3ons (2008), 79

p. 608

Ibid. p. 61180

Ibid. p. 61281

Elizabeth A. Kensinger & Daniel L. Schacter, ‘Memory and Emo7on’, Handbook of Emo3ons (2008), 82

p. 620

Elizabeth A. Kensinger, ‘Remembering the Details: Effects of Emo7on’, Emo3on Review, Vol. 1, Issue 83

2 (2009), pp. 99-113

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with emotional content as they were intrinsic details now rather than when they in series of words. This relates to hypothesis that suggest that the effect of emotions on memory is trade-off which means that some aspects of an information are more likely to be remembered due to their emotional aspect as opposed to other aspects that are more likely to be forgotten. Though emotions still 84

enhance the aspect of memory that has emotional content it is often done at the expense of the other information. Another finding is that emotion affecting the amount of detail does not affect the overall proportion of information remembered. Other studies focusing on recognition found that there was 85

higher probability for non-emotional things to be correctly recognized than the emotional ones. This is because emotional emotions are processed in more fluent way than the neutral ones and therefore some errors arise such as confusion about the time we encountered the item.

However, the amount and accuracy of detail is very subjective and hard to investigate since an individual might not remember certain event as well but confidence in the details will cause him to believe that he actually remembers the event accurately. The perfect examples can be the recognition paradigms mentioned previously. Repressed Memories There are two phenomena that could happen to a memory that contains strong emotionally negative information: suppression and repression. Suppression is a conscious process that deliberately pushes a memory out of an individual’s awareness due to its negative effect on his mind. These memories can be retrieved when the person is asked about them. Repression is a form of suppression that happens unconsciously and causes the memory to be blocked out of conscious perception. Repressed memories occur as a result of traumatic event in a person’s life that emotionally overwhelmed him. These cannot be retrieved unless a specific cue is presented that may trigger the process of recall though this person sometimes might not even recognize these. Those who experienced repression 86

often realize that some traumatic event has happened but cannot remember anything more.

It is very difficult to determine the mechanism responsible for repressed memories as it can differ among individuals. However, some possible mechanisms have been introduced. Firstly, during a traumatic event the activity certain brain regions show significant change in activity. Hippocampus might exhibit low activity and thus affecting long-term memory while prefrontal cortex will have increased activity. Secondly, it has been suggested that changes in brain wave rhythms are responsible for repression. This can be shown on EEG (electroencephalograph) where fast wave activity occurs in different regions that usually while there is slow wave activity in regions of conscious perception. Traumatic event comes with large release of stress hormones that have been discussed previously and that can alter previous two effects as well as neural transmission. The change in neurotransmission results in low levels of serotonin and dopamine and therefore strong negative feeling. The main role though behind this plays the sympathetic NS that extremely active while parasympathetic NS is underactive and so person cannot relax and therefore all of these things could occur. 87

Elizabeth A. Kensinger & Daniel L. Schacter, ‘Memory and Emo7on’, Handbook of Emo3ons 84

(2008), p. 621

Ibid. 85

Dak Mar7n, ‘Repressed Memories’, Lucid Pages h_p://www.lucidpages.com/rmem.html [last 86

accessed on 14.12.2016]

‘Repressed Memories: Causes, Mechanisms, & Coping Strategies’, Mental Health Daily, h_p://87

mentalhealthdaily.com/2015/06/15/repressed-memories-causes-mechanisms-coping-strategies/ [last accessed on 14.12.2016]

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There is a lot of controversy around repressed memories as there are people that believe these do not actually exist and they are only pseudo-memories or that these are a kind of ‘blending’ between false and actual memories. Another idea is that they could not exist due to lack of objective evidence. 88

Emotional Context and Memory It has been established that emotional content of an information has a significant impact on ability to remember it. However, so far the effect of emotional context has not been discussed. A certain study investigates how the emotional context of an individual, induced positive or negative emotion, impacts encoding of an emotionally neutral information. The relationship between emotional 89

context and recall has been researched before as it is form of mood-dependent recall though research into its effect on encoding has been sparse. Researchers were studying the brain of participants using fMRI during encoding of the neutral information given to investigate subsequent memory effect (SME). SME is increased brain activity during encoding for later successfully remembered information compared to the forgotten one. Participants were presented with positive, negative and 90

neutral pictures, that were similarly image and colour complex, to trigger emotional response. It is important to note that they differed in the level of arousal. These were then followed by emotionally neutral words that they were supposed to remember. They were later on asked to recall these words. The results showed that emotional context does correlates with certain increase in SME. Interestingly, the data show that there is discrepancy between influence of positive and negative emotional context. Positive emotional encoding context was accompanied by activation in the right anterior parahippocampal and fusiform gyrus while the negative one showed activation in the amygdala. 91

This means that there must be two separate processes that influence memory according to the valence of the emotional context. However, surprisingly the results say that the increase in amount of remembered information only occurred during positive emotional context but it was same as neutral during negative emotional context. On the other hand, another study that investigated the effect of 92

mood of individuals on memory encoding found out that both positive and negative mood has influence on encoding while positive mood has greater enhancing effect. Their results supported the 93

notion that there are different systems for various valence of mood or emotional context. The differences may arise due to the fact that mood is long-lasting state and also differences in the procedure of the experiment. The first study also had smaller sample size compared to the other one though both have relatively small number of participants. Therefore, there are further studies needed to be done to clarify the results.

The Effect of Emotions on Non-Declarative Memory Implicit memory can be affected by emotions by changing future behaviour according to previous experiences. It has been suggested that emotional response itself is an expression of implicit memory. For example, there is an anecdote about a certain doctor that pricked his patient suffering 94

from Korsakoff’s syndrome (a chronic memory disorder that is associated with anterograde and

Ibid.88

Erk Susanne, Kiefer Markus, Grothe Jo, Wunderlich Arthur P., Spitzer Manfred & Walter Henrik, 89

‘Emo7onal Context Modulates Subsequent Memory Effect’, Neuroimage, Vol. 18 (2003), pp. 439-447

Ibid. p. 44090

Ibid. p. 44691

Ibid.92

Kiefer Markus, Schuch Stefanie, Schenck Wolfram & Fiedler Klaus, ‘Emotion and Memory: Event-93

related Potential Indices Predictive for Subsequent Successful Memory Depend on the Emotional Mood State’, Advances in Cognitive Psychology, Vol. 3, no. 3 (2007), pp. 363-373

Kihlstrom J.F., Tobias B.A., Mulvaney S. & Tobis I.P., ‘The Emotional Unconscious’, Cognition 94

and Emotion (2000)

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retrograde amnesia ) with a pin hidden in his hand causing her to feel slight distress. Then the doctor 95

left the room and returned a bit later. At this point the patient couldn’t recognize him or recall the incident. However, when the doctor wanted to shake her hand, she pulled her hand away and refused to touch the doctor’s hand. When asked for a reason the patient replied: “Sometimes people hide pins in their hands”. Therefore the emotional response to doctor’s attempt to shake hands was due to 96

previous experience and so non-declarative memory that was acquired unconsciously. There have been few other studies done with the aim to support the idea of emotion being recollection of implicit memory. However, these are very sparse and there is need to carry out more of experiments looking at this relationship. There is also possibility that the processes behind this effect are similar as those with declarative memory even though there hasn’t been sufficient evidence to support it.

Non-declarative memory can also have many forms and one of them is priming that several studies focused on. Priming results in changes in person’s perception or response to stimuli because of previous exposure. These studies show that emotional stimuli have greater impact on priming task 97

than the non-emotional ones and therefore emotions have enhancing effect on priming in similar way as on explicit memory. There are other such as fear conditioning which name even suggests an involvement of emotions in forming of these procedural memories.

Unknown, ‘Korsakoff’s Syndrome’, Alzheimer’s Association, http://www.alz.org/dementia/95

wernicke-korsakoff-syndrome-symptoms.asp [last accessed 14.12.2016]

Kihlstrom J.F., Tobias B.A., Mulvaney S. & Tobis I.P., ‘The Emotional Unconscious’, Cognition 96

and Emotion (2000)

Elizabeth A. Kensinger & Daniel L. Schacter, ‘Memory and Emotion’, Handbook of Emotions 97

(2008), pp. 601-617

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Analysis The aim of this report was to investigate the ways in which emotions influence human memory. It is clear that emotions have a great impact on memory which was investigated mainly in two ways, by studying the activity of the hippocampus and the amygdala in healthy and impaired brains as well as testing the amount remembered by the participants. Due to the complexity of this relationship, it can be investigated from many different points of view. We could compare the influence it has on declarative and non-declarative memory, whether they have enhancing or impairing effect on memories, its influence on different stages of memory formation and retrieval or various aspects of a memory as well as compare influence on emotional content as opposed to context.

Both declarative and no-declarative memories are influenced by emotions in certain ways. Implicit memories are considered to be expressed by emotional response so it can be enhanced by the emotional stimuli, however, the research into this has been weak due the unconscious nature of implicit memory. On the other hand, declarative memories seem to be influenced by emotions by both enhancing and impairing sense. The connection between emotions and declarative memories seems to be much more complex and have been also studied more as it is within our awareness. Though it is important to recognize that this seemingly less complex and significant effect of emotions on implicit memory might be simply due to lack of evidence and information as it has potentially great survival and adaptive role.

Declarative memory has been investigated in terms of the effect of emotions on memory encoding, consolidation and subsequent storing and retrieval. Encoding is enhanced for emotional information by directing attention towards it but in doing so decreasing the likelihood of other information to be encoded. This increased attention also makes experiments on consolidation and retrieval of emotional item more difficult as it is difficult to determine whether the differences are just due to increased focus on it or not. The process of consolidation is influenced by arousal emotions as they are accompanied by release of stress hormones that will through complex mechanism increase long-term potentiation and therefore increase probability of an information to by stored. This has generally positive impact on memory except for chronic stress that due to long-term release of stress hormones like cortisol hinders consolidation and storing of memory. Retrieval of memory with emotional content is most efficient when the mood of the person either matches the content or mood at encoding. This might be considered as both advantageous and disadvantageous. This is because, on one hand, when your mood matches the memory recall is more efficient; on the other hand, when this match is not there, it is harder to recall that emotional memory and therefore recall is less efficient.

Another way of assessing emotional effect is looking at the different aspects of memory. The quantity of remembered information is increased when having emotional content, however, difference in valence doesn’t show clear trend and so it is probably high arousal of emotions that affects the quantity. The vividness of memories also shows increase when emotional stimuli are introduced. The quality is influenced by both valence and arousal of emotions as opposed to quantity. High arousal emotion results in greater vividness of the memory. The valence of emotion and memory, when investigated in laboratory, showed that negative cues tend to be remembered with better quality than positive ones. However, outside the laboratory this trend doesn’t work very well as there are many other factors of both emotions and memory that can affect the level of quality. Lastly, the accuracy and amount of detail of memory is affected by emotions in a different way as compared to other two aspects. The emotional content of an information causes some parts of a memory to be more likely to be remembered than the others due to focus on the emotional ones. This can culminate in forgetting of certain details making the memory less accurate. An issue with investigating this aspect is that it is very subjective and difficult to quantify and often as well as knowing whether the individual is actually accurate or is just overconfident about the details.

An argument supporting the notion that emotions impair memory could be repressed memory as they result from strong negative or traumatic event and are pushed out of the awareness completely which can often be caused by incorrectly remembering the event. However, this is weakened by the fact that many people and also professionals believe that these repressed memories do not actually exist as they argue either that they are just special cases of normal memories and false memories or that we are lacking objective evidence to support them.

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Lastly, the difference between the effect of emotional content and context can be discussed. There have been much more studies done concerning emotional content while only few investigate emotional context as well. The emotional context of remembered information influenced the amount of items encoded as expected though it showed that positive emotional context had much greater influence than negative one which had barely any. They also were predicted by activation of various parts of the brain which was not seen during investigations of emotional content effect. This therefore suggests slightly different mechanisms in these two cases involvingt a bit different brain regions which could explain the discrepancies.

During studies that did not involve fMRI, there is a difficulty to achieve comparable situations so that the results as reliable as possible. The biggest difficulties arise from producing the stimuli with various valence as similar in the other criteria as possible. The other difficulty is that each individual is different and as mentioned the evolution of memory processes ensures that the information remembered is the most relevant to individual’s desires or needs. This means that since the goals and needs can change from individual to individual also tendency to remember certain emotional information can be altered. Thus, in order for the studies to be reliable the sample should be large which was not the case for all of these studies. For example, the study about emotional context and SME worked with only ten participants and even though their tests were repeated several times, the 98

specificity of each individual could alter the results. A possible way to make these experiments more reliable could be making a questionnaire or interviewing the participants in order to find out what would affect them the most such as fears or preferences and so customize the stimuli. However, there has to be certain balance in order for the results to remain comparable.

Studies using fMRI can be considered to be more precise in terms of quantifying the data, however, they face the similar issues as the other studies like the uniqueness of an individual. The issue that can arise here even more significantly is that in these experiments there are often people with different brain lesions involved that can both be difficult to find and therefore sample size is often relatively small and also the impairment differs between individual and therefore it is not a constant but a variable as well.

Conclusion To conclude, emotions affect memory in many complex ways that could be looked at from different angles. The emotional content or context of an information usually results in enhanced memory representation except for cases such as chronic stress or repressed memories. However, this enhancement can cause impairment of other neutral information during some processes or lack of the accuracy and amount of the detail. There are still further investigations needed to be done to clarify many aspects of this relationship between emotional and memory systems.

Erk Susanne, Kiefer Markus, Grothe Jo, Wunderlich Arthur P., Spitzer Manfred & Walter Henrik, 98

‘Emo7onal Context Modulates Subsequent Memory Effect’, Neuroimage, Vol. 18 (2003), pp. 439-447, p. 440

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