Neurology of Memory Neurology of Memory SystemsSystems

ReviewReview

ConditioningConditioning Habituation/SensitizationHabituation/Sensitization

Working MemoryWorking Memory Phonologic Phonologic Visual/Spatial SketchpadVisual/Spatial Sketchpad Central ExecutiveCentral Executive

Long-Term-MemoryLong-Term-Memory ImplicitImplicit ExplicitExplicit

Brain SystemsBrain Systems

ConditioningConditioning

The The AplysiaAplysia

Also called a sea slugAlso called a sea slug It is a mollusk with nervous system It is a mollusk with nervous system

containing only about 5000 neuronscontaining only about 5000 neurons Has specific reflexes: touching the Has specific reflexes: touching the

animal causes the gill to be pulled animal causes the gill to be pulled inward inward

This animal has made it easy to study This animal has made it easy to study the basic neural systems of learning the basic neural systems of learning

HabituationHabituation

Due to Due to Synaptic DepressionSynaptic Depression There is a decrease in the release of There is a decrease in the release of

neurotransmitterneurotransmitter The transmitter is not used up but rather The transmitter is not used up but rather

the the repeated stimulation causes a the the repeated stimulation causes a change in the ion flow which would change in the ion flow which would normally trigger the transmitter to be normally trigger the transmitter to be releasedreleased

PicturePicture

Sensitization Sensitization

Occurs at the same synapse but by the Occurs at the same synapse but by the actions of another neuron terminal actions of another neuron terminal (interneuron)(interneuron)

A shock to the tail activates the release of A shock to the tail activates the release of a (stimulant) neurotransmitter that causes a (stimulant) neurotransmitter that causes the terminal to change the flow of ionsthe terminal to change the flow of ions

This time the change in ions causes more This time the change in ions causes more neurotransmitter to be releasedneurotransmitter to be released

PicturePicture

DurationDuration

A single training session of 10 touches give A single training session of 10 touches give rise to learning that lasts minutes (STM-LTP rise to learning that lasts minutes (STM-LTP and no protein)and no protein)

Four training sessions of 10 trials a day Four training sessions of 10 trials a day (spaced over four days) give rise to learning (spaced over four days) give rise to learning that lasts at least three weeks (LTM-requires that lasts at least three weeks (LTM-requires protein synthesis)protein synthesis)

Overall it seems that learning takes places Overall it seems that learning takes places relatively quicklyrelatively quickly

Conditioning of FearConditioning of Fear Typically a shock will be used to evoke a fear Typically a shock will be used to evoke a fear

response (increased heart rate)response (increased heart rate) A small lesion was made in the hypothalamus A small lesion was made in the hypothalamus

(believed to be involved in the control of the (believed to be involved in the control of the cardiovascular system)cardiovascular system)

There was no longer an increase in heart rate due to There was no longer an increase in heart rate due to the tone. There was still an increase in heart rate the tone. There was still an increase in heart rate due to shockdue to shock

The behavior stayed the same, but the physiological The behavior stayed the same, but the physiological learned fear response no longer existed learned fear response no longer existed

Amygdala projects to the hypothalamusAmygdala projects to the hypothalamus

Conditioning Motor ResponseConditioning Motor Response

Eyeblink conditioning involves a learned Eyeblink conditioning involves a learned motor responsemotor response

A small lesion in the cerebellum abolishes the A small lesion in the cerebellum abolishes the learning and memory of a conditioned motor learning and memory of a conditioned motor responseresponse

Is the memory actually stored there? Yes!!Is the memory actually stored there? Yes!! This is the only long-term memory trace that This is the only long-term memory trace that

has been localized in the mammalian brainhas been localized in the mammalian brain

Brain SystemsBrain Systems

Working memoryWorking memory

Visual Sketchpad and the BrainVisual Sketchpad and the Brain

Monkey learned a STM task where the Monkey learned a STM task where the food was under the new objectfood was under the new object

Lesions of the hippocampus disrupted Lesions of the hippocampus disrupted STM of what they had seen and they STM of what they had seen and they could not tell the difference between old could not tell the difference between old and new objectand new object

They could discriminate between They could discriminate between objects, so visual perception was intactobjects, so visual perception was intact

Spatial Sketchpad and the BrainSpatial Sketchpad and the Brain

Monkey learned a spatial STM taskMonkey learned a spatial STM task Destruction of a region of frontal cortex Destruction of a region of frontal cortex

severely disrupts the ability to perform severely disrupts the ability to perform the taskthe task

The monkey can still perform the visual The monkey can still perform the visual STM taskSTM task

Continuous Brain ActivityContinuous Brain Activity

Monkeys were trained to remember a color Monkeys were trained to remember a color for 16 seconds (the temporal lobe activated for 16 seconds (the temporal lobe activated during color perception)during color perception)

Recording brain activity showed that during Recording brain activity showed that during the 16 sec, there was continuous activity in the 16 sec, there was continuous activity in the temporal lobethe temporal lobe

Continuous activity has also been found Continuous activity has also been found during remembering tasks in other sensory during remembering tasks in other sensory areas of the brain areas of the brain

Frontal LobeFrontal Lobe

The frontal lobe is also continuously active The frontal lobe is also continuously active during a remembering taskduring a remembering task

It is possible to disrupt the continuous activity It is possible to disrupt the continuous activity in (say) the temporal lobe during a color in (say) the temporal lobe during a color remembering task, but continuous activity in remembering task, but continuous activity in the frontal lobe remains continuous the frontal lobe remains continuous

This is neurologic evidence that the frontal This is neurologic evidence that the frontal lobes have executive control over other lobes have executive control over other processing systemsprocessing systems

Memory SystemsMemory Systems

Long-Term-MemoryLong-Term-Memory

LTM & STM Storage AreasLTM & STM Storage Areas

How do the short-term and long-term forms of How do the short-term and long-term forms of memory relate to each other, and do they memory relate to each other, and do they occur at the same or different locations?occur at the same or different locations?

It seems that short-term learning results in It seems that short-term learning results in connections simply being depressed or connections simply being depressed or stimulated. Long-term learning involves stimulated. Long-term learning involves inactivation or forming of new connectionsinactivation or forming of new connections

Thus, the same synaptic connections that are Thus, the same synaptic connections that are used in a STM are also used in a LTMused in a STM are also used in a LTM

Medial Temporal LobeMedial Temporal Lobe

This structure seems to be the gateway This structure seems to be the gateway into LTM from STMinto LTM from STM

However, the structure is not the However, the structure is not the repository of LTMrepository of LTM

LTMs are thought to be stored in the LTMs are thought to be stored in the same distributed set of structures that same distributed set of structures that perceive, process, and analyze what is perceive, process, and analyze what is to be rememberedto be remembered

LTM Storage AreasLTM Storage Areas

Activity in the inferior temporal lobe was Activity in the inferior temporal lobe was recorded while monkeys viewed visual recorded while monkeys viewed visual patterns. Found that specific neurons patterns. Found that specific neurons responded best to specific picturesresponded best to specific pictures

Monkeys learned 12 picture pairs Monkeys learned 12 picture pairs Before one neuron responded to one picture. Before one neuron responded to one picture.

After learning, a neuron responded to the After learning, a neuron responded to the original picture and the picture that was original picture and the picture that was paired with itpaired with it

Hippocampal DamageHippocampal Damage

Damage to the hippocampal system not Damage to the hippocampal system not only impairs new learning but also can only impairs new learning but also can disrupt recent memorydisrupt recent memory

Thus, memory is not fixed at the time of Thus, memory is not fixed at the time of learning but takes time to develop a learning but takes time to develop a permanent formpermanent form

Establishing LTMEstablishing LTM

Memory does not start in the hippocampus Memory does not start in the hippocampus and diffuse out to the cortical areas, but and diffuse out to the cortical areas, but rather is always in the cortexrather is always in the cortex

The medial temporal lobe stores some aspect The medial temporal lobe stores some aspect of the information for a significant period after of the information for a significant period after learninglearning

One idea is that the medial temporal lobe One idea is that the medial temporal lobe stores links or pointers that connect multiple stores links or pointers that connect multiple cortical areascortical areas

Implicit/Explicit and the BrainImplicit/Explicit and the Brain Using PET, brain activity was recorded during implicit Using PET, brain activity was recorded during implicit

and explicit memory tasksand explicit memory tasks Subjects learned a list of words: In the explicit Subjects learned a list of words: In the explicit

condition, they had to remember the words during the condition, they had to remember the words during the 40 sec scan. In the implicit condition a word stem 40 sec scan. In the implicit condition a word stem completion task was usedcompletion task was used

In the explicit test there was more activity in the In the explicit test there was more activity in the hippocampus, but in the implicit test there was more hippocampus, but in the implicit test there was more activity in the visual areasactivity in the visual areas

Thus, implicit and explicit memory seem to be in Thus, implicit and explicit memory seem to be in different brain regionsdifferent brain regions

Memory SystemsMemory Systems

The Adaptable NeuronThe Adaptable Neuron

LTPLTP

The process that lead to long-term changes The process that lead to long-term changes in the neuron is called long-term-potentiation in the neuron is called long-term-potentiation (LTP)(LTP)

Found in the lab when a brief high-frequency Found in the lab when a brief high-frequency period of electrical activity was applied period of electrical activity was applied artificially to pathways in the hippocampusartificially to pathways in the hippocampus

The result was an increase in “synaptic The result was an increase in “synaptic strength” lasting for days or weeks strength” lasting for days or weeks (depending)(depending)

How Do LTPs Work?How Do LTPs Work?

It is very complicated and it dose not work the It is very complicated and it dose not work the same in all regions of the brainsame in all regions of the brain

LTP is associated with an increased LTP is associated with an increased probability that neurotransmitters will be probability that neurotransmitters will be releasedreleased

Oddly enough, increasing the probability of Oddly enough, increasing the probability of neurotransmitter release results from a neurotransmitter release results from a chemical message (nitric oxide?) sent from chemical message (nitric oxide?) sent from the post-synaptic nerve terminalthe post-synaptic nerve terminal

Need More Than LTP to Make a Need More Than LTP to Make a Long-Term-Memory --ProteinLong-Term-Memory --Protein The switch from STM to LTM is The switch from STM to LTM is

complicatedcomplicated Communication between neurons will Communication between neurons will

trigger special a regulatory protein that trigger special a regulatory protein that regulates gene (DNA) expression in the regulates gene (DNA) expression in the nucleus of the neuronnucleus of the neuron

DNA produce new proteins that add to DNA produce new proteins that add to the physical structure of the neuronthe physical structure of the neuron

Growing New SynapsesGrowing New Synapses

Protein production builds new synapses Protein production builds new synapses between neuronsbetween neurons

As time passes and there is no further As time passes and there is no further use of the synapses the new synaptic use of the synapses the new synaptic terminals are lostterminals are lost