Cognitive & Neuroscience Intro Themes –cognitive psychology has been guided by an information...

Cognitive & Neuroscience IntroCognitive & Neuroscience Intro

• Themes– cognitive psychology has been guided by an

information processing approach to theorizing– this approach attempts to characterize how

information is processed from its initial input until its response

– this approach continues to be used


• Primary measures– Reaction time (RT)

measure the elapsed time from the onset of a stimulus until there is a response to the stimulus

general goal of measuring RT is to make inferences about underlying cognitive processes (which are assumed to take time)


• Primary measures– Accuracy

this measure assesses the accuracy of an individual’s performance

Note: accuracy can be broadly (or narrowly) definede.g., verbatim versus gist recall


• Analogies– channel capacity

early uses: attention/Broadbentmore recent uses: controlled processing

– computer analogyserial sequential processing of information

Atkinson-Shiffrin ModelAtkinson-Shiffrin Model

(Atkinson & Shiffrin, 1968)


• General early assumptions– sequential stages of processing– stages are independent– stages are non-overlapping


• New conceptualizations– parallel processing

e.g., typing

– hierarchical organizatione.g., typing a worde.g., grasping an object (prepare index finger thumb

apperture as you move arm toward object)

– context effectssemantic priming


• Cognitive neuroscience intro– neuron is the basic building block of the brain

cell that is specialized for receiving and transmitting a neural impulse

Note: there is enormous variability in the structure of neurons


• Development of neurons and glial cells– germinal (or stem) cells of an embryo give rise to

two types of nervous system cells: neuroblasts and spongioblasts (blast is an immature cell)

– neuroblasts develop into neurons– spongioblasts develop into glial cells

glial cells provide support to neurons


• Cognitive neuroscience intro– Major structures of a neuron

input end: dendrites, which accumulate neural stimulation into the neuron itself

cell body or soma: regulates the biological activity of the neuron

axon: a long tube-like structure used to transmit information

axon terminals or terminal arborizations:output end of the neuron, where neural impulses end

An illustration of the various structures of the neuron. The lower diagram illustrates a

sensory-motor reflex arc

An illustration of the various structures of the neuron. The lower diagram illustrates a

sensory-motor reflex arc


• Basic elements of nervous system– how a simple reflex works (e.g., jerking hand away

from a hot stove)receptor cells in hand react to physical stimulus and that

triggers a pattern of firing down a sequence of sensory neurons

tracts of sensory neurons pass message along into the spinal cord where it is routed to brain and back into motor neurons

However, at the synapse the message can route directly to the motor neurons


• Basic elements of nervous system– motor neurons in spinal cord transmit message

back to arm muscles– these terminate at effector cells, which connect

directly to muscle fibres and cause the muscles to pull arm away from hot stove

– brain route: message is routed up spinal cord to brain (CNS) note: central nervous system = spinal cord + brain


• Basic elements of nervous system– synapse: region where the axon terminals of one

neuron and dendrites of another neuron come together

– synapses are small gaps between neuronsany single neuron synapses on a large number of other

neurons: called divergence (a typical neuron synapses on from 100-15,000 other neurons)

also any single neuron is the destination of many neurons (called convergence)


• Basic elements of nervous system– information is transmitted across a synapse chemically

by means of a neurotransmitter– a neurotransmitter is released from small buttons or

sacs in the axon terminals, which then fit into receptor sites on the dendrites of the next neuron

– two types of neurons: inhibitory and excitatory– inhibitory neurons decrease the likelihood of the next

neuron from firing; excitatory neurons have the opposite effect


• Structure of Nervous System– Nervous system consists of two major parts: central

nervous system (CNS) and peripheral nervous system (PNS)

– PNS consists of: skeletal nervous system and autonomic nervous system

– Skeletal system controls striated (i.e., striped) muscles, which are under voluntary control, and play an important role in motor cognition and simulation


• Structure of Nervous System– autonomic nervous system governs smooth

muscles and some glands– Smooth muscles, found in heart, blood vessels,

stomach lining, and intestines, are not usually under voluntary control


• Structure of Nervous System– autonomic nervous system plays a key role in

emotion and affects memory functioning– Autonomic nervous system is divided into

sympathetic and parasympathetic nervous system


• Structure of Nervous System– sympathetic nervous system prepares animal to

respond more vigorously in an emergency (flight-or-fight response). Some changes:

– Increasing heart rate (and delivering more oxygen and nutrients to organs)

– Increasing breathing rate (and providing more oxygen)– Dilating pupils (increasing sensitivity to light)– Reducing digestive function


• Structure of Nervous System– parasympathetic nervous system counters

sympathetic nervous system and dampens the organism’s responses


• Cerebral cortex (Overview)– Brain should be thought of as a collection of

components that work together– It consists of two halves, which are called the left

and right cerebral hemispheres– Hemispheres are connected by a massive

collection of nerve fibres called the corpus callosum, as well as several smaller connections


• Cerebral cortex (Overview)– Beneath the skull is a membrane covering the

brain called the meninges– Beneath that is a network of blood vessels

clinging to the surface of the brain– The surface of the brain contains most of the cell

bodies of the neurons, which have a gray colour, hence the term gray matter


– Cerebral cortexcortex: consists of 4-6 layers of cells (or gray matter)the term cortex (bark) refers to any outer layer of cellsconventionally the terms cortex and neocortex are

used interchangeablythe cortex is wrinkled in order to increase its area

(think of crumpled paper)


• Cerebral cortex– Clefts (indentations) in the brain are called

fissures if they extend deeply into brain or sulci if they are shallower

– A ridge in the cortex is called a gyrus

Gyri and sulci. Lateral (A) and medial (B) views of the gyri. Lateral (C) and

medial (D) views of the sulci

Gyri and sulci. Lateral (A) and medial (B) views of the gyri. Lateral (C) and

medial (D) views of the sulci


• Subcortical structures– Beneath the cortex are found subcortical

structures and at the centre of the brain are a series of cavities, called ventricles

– Ventricles are filled with the same fluid that is found in the spinal cord


• hemispheres and lobes– cortex consists of two hemispheres separated by

the medial longitudinal fissure– each hemisphere is divided into four lobes

frontal lobe (behind forehead)temporal lobe (underneath temples)occipital lobeparietal lobe

The location of the frontal, parietal, occipital, and temporal lobes of the

brain

The location of the frontal, parietal, occipital, and temporal lobes of the

brain


• Lobes– The cognitive activities are not assigned specifically to

one of the lobes and the lobes are involved in several cognitive activities

– A rough guide– occipital lobes

– processes visual input from eyes and from memory (visual imagery, some)

Within the occipital lobe specific different regions process different aspects of vision (e.g., motion, color, shape)

if occipital lobes are damaged blindness results


• Lobes– temporal lobes

Involved in several functionsRetention of visual memoryMatching visual input to visual memoryProcess input from the earsPosterior region of the left temporal lobe (Wernicke’s area is

crucial for comprehending languageAnterior regions of temporal lobes are crucial for processing new

memories, deriving meaning, and processing emotion


• Lobes– Parietal lobes

Involved in several functionsIts most anterior gyrus, the somatosensory cortex

(area S1), represents sensations on different parts of your body with left S1 representing right side of body and vice versa for right S1

Parietal lobes are also involved in representing space and your relationship to it, and in representing tool knowledge


• Lobes– Frontal lobes

Involved in several functionsManaging sequences of behaviors or mental activitiesMajor role in producing speech—Broca’s area of left hemisphereControlling movements– area M1 (most posterior gyrus of frontal

lobes (also called motor strip); this area is immediately adjacent to S1

Left M1 controls movements by right part of body and vice versaFrontal lobes also involved in memory retrieval, in planning and

reasoning, and in some emotions


• Projection maps– constructed by tracing axons from sensory

systems into the brain, and by tracing axons from the neocortex into the motor systems of the brain stem and spinal cord


• Projection mapsdark areas in figure are primary projection areas.

These areas receive input from the sensory systems or project to the spinal motor systems

lightly shaded areas receive projections (input) from the primary projection areas and are called secondary projection areas

unshaded areas are called higher-order association or tertiary areas


• Topography of the neocortex– primary projection areas

visual system--occipital lobesauditory system -- temporal lobessomatosensory system -- parietal lobesmotor system -- frontal lobes

A projection mapA projection map

Subcortical structuresSubcortical structures


• Subcortical areasthalamus consists of several nuclei; all sensory

systems except for smell have relays here on their way to cortex; also different cortical regions communicate with each other via thalamus


• Thalamus– consists of two symmetric nuclei at base of cerebral

hemispheres superior to hypothalamus– each hemisphere contains half of the thalamus– thalamus receives ascending input (sensory information)

and descending input from cerebral hemispheres, particularly from those cortical regions to which it projects

– all sensory systems except for smell have relays here on their way to cortex


• Thalamus– can be thought of as a complex relay station for

sensory and motor systems except for olfaction (smell)

– thalamus is thought to play an important role in the classification, integration of information, before sending it to the cortex for further processing


• Thalamus– Thalamus also plays an important role in

selective attention – Pulvinar nucleus (a nucleus refers to a cluster of

cells) is involved in focusing attention


– hypothalamus composed of small nuclei; involved in feeding, sexual behaviour, sleeping, temperature regulation, blood pressure, heart rate, etc.

– Some of these functions are accomplished by hormones (chemicals that affect various organs)

– Hippocampus located at the anterior end of the temporal lobes; it plays a central role in entering new information into memory although it is not where memories are stored; it governs processes that allow memories to be stored


– Amygdala (named, from Greek, because of its almond shape) plays an important role in the appreciation of emotion in others and in the expression of our own emotion (esp. fear)

– The amygdala can modulate the functioning of the hippocampus; this helps you store vivid memories of highly emotional information

– The amygdala and hippocampus along with other structures are part of the limbic system, which used to be thought to regulate emotion

Model of the human limbic system and its major structures

Model of the human limbic system and its major structures


• Basal ganglia– collection of nuclei lying beneath the anterior regions

of the neocortexinclude the putamen (shell), the globus pallidus (pale globe),

the caudate nucleus (tailed nucleus), and the amygdala (almond). [Note: striatum = putamen + caudate; globus pallidus = pallidum]

caudate nucleus receives projections from all parts of the neocortex and then projects through the putamen and globus pallidus to the thalamus, and then to the motor areas of the cortex


• Basal gangliabasal ganglia also has reciprocal connections to the

substantia nigra (black area)this projection provides dopamine to the basal ganglia;

when dopamine is lost a motor disorder called Parkinson’s disease results


• Basal ganglia– functions of basal ganglia

involved in motor function--including postural changes, sequencing of movements into a smoothly executed response, and habit learning

Habit learning (e.g., development of routinized activities such as coming to this lecture hall)

Relation between the basal ganglia and the cortex. Arrows indicate theoretical

projections of the various areas into basal ganglia structures

Relation between the basal ganglia and the cortex. Arrows indicate theoretical

projections of the various areas into basal ganglia structures


• Brainstem– Includes the pons and medulla and reticular

formation– regulates many movements of animals– responds to sensory features of the environment– regulates eating, sleeping, drinking, body

temperature

The three divisions of the brainThe three divisions of the brain


• Topography of the neocortex– The remaining functional neuroanatomy slides,

about 6, contain additional useful, reference information

– You will not be tested on this material

Medial view through the center of the brain showing structures of the

brainstem

Medial view through the center of the brain showing structures of the

brainstem


• Topography of the neocortex– cytoarchitectonic maps

constructed by examining the neurons in the neocortex to identify regions that have unique organization

the best known of these is called Brodmann’s map shown in Figure 3.9

Brodmann’s areas of the cortexBrodmann’s areas of the cortex


Function Brodmann area

Vision, primary 17

Vision, secondary 18,19, 20, 21,37

Auditory, primary 41

Auditory, secondary 22, 42

Body senses, primary 1, 2, 3

Body senses, secondary 5, 7


Function Brodmann area

Motor, primary 4

Motor, secondary 6

Eye movement 8

Speech 44

E = mc2

???

The First “Brain Imaging Experiment”The First “Brain Imaging Experiment”

“[In Mosso’s experiments] the subject to be observed lay on a delicately balanced table which could tip downward either at the head or at the foot if the weight of either end were increased. The moment emotional or intellectual activity began in the subject, down went the balance at the head-end, in consequence of the redistribution of blood in his system.”

-- William James, Principles of Psychology (1890)

Angelo MossoItalian physiologist

(1846-1910)

… and probably the cheapest one too!

Courtesy: J. Culham, Robarts Research Institute

Brain imaging and cognitionBrain imaging and cognition

• Brain imaging techniques– early 1970s x-ray computed tomagraphy or x-ray CT

technique developed– when highly focused x-rays are passed through the

body, the beam is affected in predictable ways by the relative density of the tissue

– by passing a beam through the body at many different angles it becomes possible (using sophisticated math techniques) to re-construct an image of the body


• Brain imaging techniques– this technique led to the development of Positron

Emission Tomography (PET)– PET also built on a technique known as

autoradiography


• autoradiographyradioactive labeled compound is injected into

organismexperiment is performedorgan is removed and sectionedindividual slices are placed on film which is

sensitive to radioactivity


• PET– PET also uses radioisotopes but does not require

organs to be removed– PET uses radioisotopes that have positrons that

emit gamma radiation that can be detected by sensors outside of the head


• PET (how it works)– a PET camera is a set of radiation detectors that

circle the subject’s head – subject is injected with positron-emitting radioactive

isotope oxygen-15 (half-life about 2 minutes)– radioactive water accumulates in brain in proportion

to the local blood flow– the greater the blood flow the more radiation counts

recorded by PET


• PET (experimental strategy)– Paired image subtraction

record image of subject while she is performing an experimental task

record image of subject while she is performing a control task

(e.g., dots in motion - stationary dots)difference tells us what brain regions are

associated with representation of motion


• PET (experimental strategy)– to eliminate noise or random variation, the

differenced images are averaged across subjects

– the slide on the following page illustrates the strategyrow 1-- experimental - control = differencerow 2 -- individualized difference imagesrow 3 -- mean difference image


• Disadvantages of PET – Invasive– Poor temporal resolution– Expensive


• What is MRI and fMRI – MRI uses strong magnetic fields to create images of

biological tissue– The strength of the magnetic field created by an MRI

scanner is measured in Tesla– MRI scanners are typically 1.5 – 3.0 Tesla (earth’s

magnetic field is 0.00005 Tesla– Refs: Smith and Kosslyn (2007); Huettal, Song, McCarthy

(2008) functional magnetic resonance imaging


• What is MRI and fMRI – To create images the scanner uses a series of changing

magnetic gradients and oscillating electromagnetic fields known as pulse sequences

– These electromagnetic fields result in energy being absorbed and then emitted by atomic nuclei in the tissue being examined

– The amount of emitted energy depends upon the number and type of nuclei present, thus creating an image of the tissue being examined


• What is MRI and fMRI – MRI structures brain structure– Important to study brain structure when it is suspected

there is neurological change to brain (e.g., stroke, dementia)

– fMRI is designed to reveal short-term physiological changes associated with the active functioning of the brain; it can also reveal patterns of brain activation associated with these changes

MRI studies brain anatomy.Functional MRI (fMRI) studies brain function.

MRI vs. fMRIMRI vs. fMRI


fMRI SetupfMRI Setup



• MRI (overview)– many atoms in the presence of a magnetic field

behave like little bar magnets or compasses– that is, they line up in a particular orientation– when a radio wave is applied to this aligned

sample, the sample emits detectable radio signals characteristic of the chemical environment


• fMRI – functional magnetic resonance imaging– nuclear magnetic resonance (NMR) image

intensity reflects the concentration of water in the sample


• fMRI – To map brain function it is necessary to create

images that distinguish between active and inactive brain regions

– Called functional contrast– This is done by measuring the metabolic

consequences of neuronal activity


• fMRI – (BOLD) contrast is a sensitive MRI marker of

neuronal activity– How BOLD works– Red blood cells contain hemoglobin– the iron ion in hemoglobin can have oxygen

bound to it or stripped off


• fMRI – How BOLD works– When brain functions it draws in more red blood

cells than it needs; by detecting extra oxygenated blood cells BOLD signal detects brain activity


• fMRI – fMRI contrast is tailored to optimize the signal

dependence on deoxyhemoglobin concentration– deoxyhemoglobin is used as a contrast agent– this so called, blood oxygenation level dependent

(BOLD) contrast is a sensitive MRI marker of neuronal activity

– MRI signal arises from the stimulation of transitions of hydrogen atoms in water, placed in a large field


• Parameters of neuroimaging data – Spatial resolution– Refers to the ability to distinguish between different

locations within an image– In 2-dimensional pictures, a pixel refers to the smallest

picture element that can be resolved.– In a satellite photo of a large region a picture element

might represent hundreds of metres, whereas a zoom picture of a region might represent 1 metre


• Parameters of neuroimaging data – Spatial resolution– In MR images, 3-dimensional samples of the

brain are obtained and the smallest resolvable 3-D element is called a voxel; in MRI, voxels are often 1 to 2 mm, in each dimension, whereas in fMRI, voxels are 3 to 5 mm on each side


• Parameters of neuroimaging data – Temporal resolution– Factors affecting temporal resolution include:– 1. the rate at which an imaging technique obtains

its images (sampling rate)– 2. the sluggishness of the physiological process

being measured; in fMRI BOLD measures blood oxygenation, a relatively slow process


• fMRI (Experimental strategy)

– acquire MR images while subjects are presented with blocks of stimulation (experimental) for about 30 seconds

– have control or baseline activity

– subtract one from the other


• fMRI– echo-planar imaging (EPI)

this technique commonly used to obtain imagesmulti-slice EPI is acquired by first exciting an nuclear

magnetic resonance (NMR) signal from a thin-slice of the head, using a shaped RF pulse in the presence of a rapidly switched magnetic field gradient

this generates a series of echoes of the NMR signal that can then be used to construct a 2-dimensional image of the slice


• fMRI– echo-planar imaging

volume data are built up by repeating the process of image acquisition at different slice positions (40 slices commonly used to cover the brain)

TR refers to the time between repeated acquisitions of the same slice

a common set of parameters is 100 ms per slice x 50 slices = 5 seconds (TR = 5 seconds)

a parameter, TE, is defined as the time needed to generate half of the echoes for a single slice

Brain Imaging: AnatomyBrain Imaging: Anatomy

Photography

CAT

PET

MRI

Source: modified from Posner & Raichle, Images of MindCourtesy: J. Culham, Robarts Research Institute


• Disadvantages of fMRI– Poor temporal resolution– Machines are:– Expensive– Noisy– Tube narrow, which some people find upsetting


• PET and fMRI are correlational methods– That is, they correlate areas of brain activation that

accompany information processing when performing a task

– Correlation does not necessarily imply causation– Brain regions that are activated may not necessarily play

a functional role in performing the task– Hence these methods only suggest which brain regions

may process information when performing a task


• PET and fMRI are correlational methods– Data from PET and fMRI can be used to compare 2 (or

more) tasks to determine whether the same or different brain regions are activated

– If different brain regions are activated, this suggests that these tasks are carried out by different processes

– If the same brain regions are activated, this provides evidence to support the claim that similar processes are involved in performing the 2 tasks


• Limitations of neuroimaging methods– Excitatory and inhibitory activity cannot be distinguished– More activation does not necessarily mean more processing– Same functional areas may be located in slightly different brain areas

making averaging across participants difficult– Brain is always active making it difficult to know what processing is

going on during ‘baseline’ condition (note: neuroimaging methods usually involve comparison of a treatment to a control condition

– Finding of no activity is difficult to interpret—could mean process is active in both conditions, inactive in both conditions or activation is subtle

– Different processes appear to be implemented in the same area (e.g., different neurons in area 17 process colour and shape)


• Other correlational methods– Other correlational methods are called electroencephalography

(EEG); event-related potentials (ERP)– In both of these methods electrodes are placed on the scalp– EEG records fluctuations in electrical activity over time, at different

“bands” or sets of frequencies (e.g., 8 – 12 cycles per second)– ERP uses electrodes to observe fluctuations in activity relative to

presentation of a stimulus (e.g., P300 is a positive fluctuation that is observed 300 milliseconds after a stimulus

– Both ERP and EEG have disadvantages: 1. Both are sensitive to muscle twitches because muscles produce electrical activity when they twitch; 2. spatial resolution poor because electrical activity detected comes from spatially distributed regions

Method Spatial Res Temporal Res

Invasive-ness

EEG Poor (1 inch)

Excellent

(ms)

Low

ERP Poor (1 inch)

Excellent

(ms)

Low

PET Good (about 1cm)

Poor High

fMRI Good (about .5 cm)

Poor Low


• Causal neural methods – It is also possible to use other methods to establish

causal connections between brain activation and behavioral performance

– Classic method is the neuropsychological patient study– Logic is straightforward—if a brain region plays a key role

in carrying out a task, a patient with damage to that region should be impaired in carrying out that task


• Causal neural methods – Brain damage can occur for a variety of reasons

including:– Stroke or other medical conditions that result in disruption

of blood flow to the brain (e.g., heart attack)– Brain surgery (e.g., to remove a tumor)– Traumatic brain injury (e.g., MVA, assault)– Brain-damaging toxins (e.g., certain drugs including

alcohol)– Brain-damaging diseases (e.g., Alzheimers, Parkinsons)


• Causal neural methods – Limitations of neuropsychological studies– Brain damage usually affects a large area of

neural tissue– It is possible that brain damage results in a

change in the functioning of the brain as a whole


• Causal neural methods – Lesions indicate necessity of region, but not sufficiency;

i.e., other brain regions may also be necessary for function

– E.g., think of a radio that won’t play music; examination of the radio revealed that its speakers were broken; conclusion that speakers are necessary for music to play is correct; however, it does not mean that a radio with undamaged speakers will necessarily play (e.g., think of a radio with a broken switch)


• Causal neural methods – Note: a given brain region may have more than

one function


• Causal neural methods – Another causal neural method is Transcranial magnetic stimulation

(TMS)– In this method brain processes of a small, circumscribed area of the

brain are disrupted (1 cubic cm)– A coil is placed on the participant’s head and a current is run through

the coil, which disrupts the neural areas of the brain beneath the coil– 2 versions of TMS– Single pulse TMS delivers a single pulse to specific brain area;

repetitive TMS (rTMS) delivers a series of pulses to specific brain area before a task is performed

– If enough pulses are delivered, this has the effect of temporarily disrupting neural processing of specific brain area (like inducing a specific lesion)


• Causal neural methods – Limitations of rTMS– Stimulating 1 brain area can affect other areas

making it difficult to infer which area is responsible for effects

– rTMS can induce seizures if it is not used according to safety guidelines

– rTMS can be used to investigate only those regions directly below the skull


• Limitations of neuroscience methods– As this overview shows, each neuroscience

method has strengths and weaknesses– This is why neuroscientists rely on evidence from

a variety of different methods (converging evidence) to understand which cognitive processes and brain regions perform specific tasks

–

Cognitive & Neuroscience Intro Themes –cognitive psychology has been guided by an information...

Documents

Transcript of Cognitive & Neuroscience Intro Themes –cognitive psychology has been guided by an information...