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Learning and Memory

H.M: Henry Molaison

Hippocampus was removed in an

attempt to cure epileptic seizures

Result: Memory disorder. He couldnot learn new words, songs or facesafter his surgery, forgot who he wastalking to as soon as he turned away,

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Memory and Learning

The formation of memories is an example of neuralplasticity

Short-term memory is accessed via the

hippocampus The hippocampus also plays a role in forming long-

term memory , which is stored in the cerebralcortex

Some consolidation of memory is thought to occurduring sleep

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Long-Term Potentiation

In the vertebrate brain, a form of learning calledlong-term potentiation (LTP) involves an increase inthe strength of synaptic transmission

LTP involves glutamate receptors If the presynaptic and postsynaptic neurons are

stimulated at the same time, the set of receptorspresent on the postsynaptic membranes changes

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Figure 49.20PRESYNAPTIC

NEURON

Glutamate Mg2

Ca 2

Na

NMDAreceptor (closed)

StoredAMPAreceptor

NMDA receptor (open)

POSTSYNAPTICNEURON

(a) Synapse prior to long-term potentiation (LTP)

(b) Establishing LTP

(c) Synapse exhibiting LTP

Depolarization

Actionpotential

2

1

3

1

2

3

4

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Figure 49.20a

PRESYNAPTICNEURON

GlutamateMg 2

Ca 2

Na

NMDAreceptor (closed)StoredAMPA

receptor

NMDA receptor (open)

POSTSYNAPTICNEURON

(a) Synapse prior to long-term potentiation (LTP)

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Figure 49.20b

(b) Establishing LTP

1

23

AMPAreceptor

NMDA receptor

Mg 2

Ca 2 Na

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Figure 49.20c

(c) Synapse exhibiting LTP

Depolarization

Actionpotential

AMPAreceptor

NMDA receptor

1 3

42

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Stem Cells in the Brain

The adult human brain contains neural stem cells In mice, stem cells in the brain can give rise to

neurons that mature and become incorporated into

the adult nervous system Such neurons play an essential role in learning and

memory

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Nervous system disorders can be

explained in molecular terms Disorders of the nervous system include:

schizophrenia, depression, drug addiction,

Alzheimers disease, and Parkinsons disease Genetic and environmental factors contribute to

diseases of the nervous system

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Schizophrenia

About 1% of the worlds population suffers fromschizophrenia

Schizophrenia is characterized by hallucinations,

delusions, and other symptoms Available treatments focus on brain pathways that

use dopamine as a neurotransmitter

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Depression

Two broad forms of depressive illness are known:major depressive disorder and bipolar disorder

In major depressive disorder , patients have a

persistent lack of interest or pleasure in mostactivities

Bipolar disorder is characterized by manic (high-mood) and depressive (low-mood) phases

Treatments for these types of depression includedrugs such as Prozac

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Addictive drugs enhance the activity of thedopamine pathway

Drug addiction leads to long-lasting changes in the

reward circuitry that cause craving for the drug

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Figure 49.23Nicotinestimulatesdopamine-releasingVTA neuron.

Inhibitory neuron

Dopamine-releasing

VTA neuron

Cerebralneuron of rewardpathway

Opium and heroindecrease activityof inhibitory

neuron.

Cocaine andamphetaminesblock removalof dopaminefrom synapticcleft.

Rewardsystemresponse

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Alzheimers Disease

Alzheimers disease is a mental deteriorationcharacterized by confusion and memory loss

Alzheimers disease is caused by the formation ofneurofibrillary tangles and amyloid plaques in thebrain

There is no cure for this disease though some drugsare effective at relieving symptoms

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Figure 49.24

Amyloid plaque Neurofibrillary tangle 20 m

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Parkinsons Disease

Parkinsons disease is a motor disorder causedby death of dopamine-secreting neurons in themidbrain

It is characterized by muscle tremors, flexedposture, and a shuffling gait

There is no cure, although drugs and various otherapproaches are used to manage symptoms

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