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Pinel basics ch09

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Copyright © 2007 by Allyn a nd Bacon Chapter 9 Learning, Memory, and Amnesia How Your Brain Stores Information This multimedia product and its contents are protected under copyright law. The following are prohibited by law: any public performance or display, including transmission of any image over a network; preparation of any derivative work, including the extraction, in whole or in part, of any images; any rental, lease, or lending of
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Page 1: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Chapter 9Learning, Memory, and AmnesiaHow Your Brain Stores Information

This multimedia product and its contents are protected under copyright law. The following are prohibited by law:• any public performance or display, including transmission of any image over a network;• preparation of any derivative work, including the extraction, in whole or in part, of any images; • any rental, lease, or lending of the program.

Page 2: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

The Brain Changes its Functioning in Response to Experience Learning –how experience changes the

brain Memory –how changes are stored and

subsequently reactivated What brain structures are involved in

processes of learning and memory?

Page 3: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Effects of Bilateral Medial Temporal Lobectomy

H.M. – an epileptic who had his temporal lobes removed in 1953

His seizures were dramatically reduced – but so was his memory

Mild retrograde amnesia and severe anterograde amnesia

Page 4: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Amnesia

Retrograde (backward-acting) – unable to remember the past

Anterograde (forward-acting) – unable to form new memories

While H.M. is unable to form most types of new long-term memories, his STM is intact

Page 5: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Assessing H.M.

Digit span – H.M. can repeat digits as long as the time between learning and recall is within the limits of short-term storage

Mirror-drawing task – H.M. exhibits improvement with practice. He is able to show skill memory – demonstrating that he can learn some things (also rotary-pursuit and a drawing task) – although he is not aware of it

Page 6: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Assessing H.M.

H.M. readily “learns” responses through Pavlovian (classical) conditioning

H.M. can learn some things, but has no memory of having learned them

Page 7: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Scientific Contributions of H.M.’s Case Medial temporal lobes are involved in

memory Short-term memory (STM) and long-term

memory (LTM) are distinctly separate H.M. is unable to move memories from

STM to LTM, a problem with memory consolidation

Page 8: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Scientific Contributions of H.M.’s Case Memory may exist but not be recalled –

as when H.M. exhibits a skill he does not know he has learned

H.M. forms new implicit memories, but not new explicit memories

Page 9: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Explicit Vs Implicit Memories

Explicit memories – conscious memories Implicit memories – unconscious

memories, as when H.M. shows the benefits of prior experience

Repetition priming tests – used to assess implicit memory – performance in identifying word fragments is improved when the words have been seen before

Page 10: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Medial Temporal Lobe Amnesia

Not all with this form of amnesia are unable form new explicit long-term memories – as was the case with H.M.

Semantic memory (general information) may function normally while episodic memory (events that one has experienced) does not – they are able to learn facts, but do not remember doing so (the episode when it occurred)

Page 11: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Effects of Cerebral Ischemia on the Hippocampus and Memory R.B. suffered damage to just one part of

the hippocampus (CA1 pyramidal cell layer) and developed amnesia

R.B.’s case suggests that hippocampal damage alone can produce amnesia

H.M.’s damage – and amnesia – was more severe than R.B.’s

Page 12: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Korsakoff’s Syndrome

Most commonly seen in who? Alcoholics Also seen in individuals with a

thiamine-deficient diet Alcohol causes a disruption in the

body’s ability to use thiamine

Page 13: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Korsakoff’s Syndrome

Characterized by amnesia, confusion, personality changes, and physical problems

Typically damage in the medial diencephalon – medial thalamus + medial hypothalamus

Page 14: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Korsakoff’s Syndrome

Amnesia comparable to medial temporal lobe amnesia in the early stagesAnterograde amnesia for episodic memories

Differs in later stagesSevere retrograde amnesia develops

Differs in that it is progressive, complicating its study

Page 15: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

What damage causes the amnesia seen in Korsakoff’s? Hypothalamic mammillary bodies?

No – Korsakoff’s amnesia is seen in cases without such damage

Thalamic mediodorsal nuclei?Possibly – damage is seen here when there is

no mammillary damage Cause is not likely to be damage to a

single diencephalic structure

Page 16: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Alzheimer’s Disease (AD)

Begins with slight loss of memory and progresses to dementia

General deficits in predementia ADMajor anterograde and retrograde amnesia in

explicit memory testsDeficits in STM and some types of implicit

memory – verbal and perceptual Implicit sensorimotor memory is intact

Page 17: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

What damage causes the amnesia seen in AD? Decreased acetylcholine

Due to basal forebrain degeneration Basal forebrain strokes can cause amnesia and

attention deficits which may be mistaken for memory deficits

Medial temporal lobe and prefrontal cortex also involved

Damage is diffuse – resulting amnesia is likely a consequence of acetylcholine depletion and brain damage

Page 18: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Posttraumatic Amnesia

Concussions may cause retrograde amnesia for the period before the blow and some anterograde amnesia after

The same is seen with comas, with the severity of the amnesia correlated with the duration of the coma

Period of anterograde amnesia suggests a temporary failure of memory consolidation

Page 19: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Gradients of Retrograde Amnesia and Memory Consolidation Concussions disrupt consolidation

(storage) of recent memories Hebb – memories are stored in the short

term by neural activity Interference with this activity prevents

memory consolidationBlows to the head (i.e., concussion)ECS (electroconvulsive shock)

Page 20: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

The Hippocampus and Consolidation What role does the hippocampus play in

consolidation? Some have proposed that memory storage

structures store memories for as long as they exist and eventually an engram forms

Engram – a change in the brain that stores a memory

Page 21: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Object-Recognition Memory

Early animal models of amnesia involved implicit memory and assumed the hippocampus was key

1970’s – monkeys with bilateral medial temporal lobectomies show LTM deficits in the delayed nonmatching-to-sample test

Like H.M., performance was normal when memory needed to be held for only a few seconds (within the duration of STM)

Page 22: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Testing object-recognition memory

Page 23: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Delayed Nonmatching-to-Sample Test for Rats Aspiration used to lesion the hippocampus

in monkeys – resulting in additional cortical damage

Extraneous damage is limited in rats due to lesion methods used

Bilateral damage to rat hippocampus, amygdala, and rhinal cortex produces the same deficits seen in monkeys with hippocampal lesions

Page 24: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Object-Recognition Deficits and Medial Temporal Lobectomy Neuroanatomical basis of resulting deficits? Bilateral removal of the rhinal cortex > object-

recognition deficits Bilateral removal of the hippocampus > no or

moderate effects on object recognition Bilateral removal of the amygdala?

No effect on object-recognition.

Page 25: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

A Paradox

Removing the hippocampus has a moderate effect on object recognition while ischemia-induced lesions to a small part of it leads to severe deficits

How can this be?

Page 26: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

A Hypothesis

Ischemia-induced hyperactivity of CA1 pyramidal cells damages neurons outside of the hippocampus

Extrahippocampal damage not readily detectable

Extrahippocampal damage is largely responsible for ischemia-induced object recognition deficits.

Evidence?

Page 27: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

A Hypothesis

Ischemia-induced hyperactivity leads to extrahippocampal damage that explains ischemia-induced object recognition deficitsBilateral hippocampectomy prevents

ischemia-induced deficitsSupported by functional brain-imaging studies

Page 28: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

The Hippocampus

Rhinal cortex plays an important role in object recognition

Hippocampus plays a key role in memory for spatial location Hippocampal lesions producesdeficits on Morris

water and radial arm mazes Many hippocampal cells are place cells –

responding when a subject is in a particular place

Page 29: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Page 30: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Comparative Studies of the Hippocampus Hippocampus seems to play a role in spatial

memory in many species – not just rats Food-caching birds - caching and retrieving is

needed for hippocampal growth Primate studies are inconsistent – no place cells Differences may be due to differences in testing

paradigms Navigating through the environment Vs location on a

computer screen

Page 31: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Theories of Hippocampal Function

Cognitive map theory – constructs and stores allocentric maps of the world

Configural association theory – involved in retaining the behavioral significance of combinations of stimuli

Involved in recognizing spatial arrangements of objects

Page 32: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Where Are Memories Stored?

Each memory is stored diffusely throughout the brain structures that were involved in its formation.

Hippocampus – spatial location Rhinal cortex – object recognition Mediodorsal nucleus – Korsakoff’s Basal forebrain – Alzheimer’s disease Damage to a variety of structures results in

memory deficits.

Page 33: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Where are memories stored?

Inferotemporal cortex – visual perception of objects – changes in activity seen with visual recall

Amygdala – emotional learning – lesion leads to lack of learned fear

Prefrontal cortex – temporal order of events and working memory

Page 34: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Where are memories stored?

Prefrontal cortex – damage leads to problems with tasks involving a series of responses

Different part of this structure may mediate different types of working memory – some evidence from functional brain imaging studies

Page 35: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Where are memories stored?

Cerebellum and striatum – sensorimotor tasks

Cerebellum – stores memories of sensorimotor skills – conditioned eyeblink, for example

Striatum – habit formation – associations between stimuli and responses

Page 36: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Synaptic Mechanisms of Learning and Memory What is happening within the brain

structures involved in memory? Hebb – changes in synaptic efficiency

are the basis of long-term memory Long-term potentiation (LTP) –

synapses are effectively made stronger by repeated stimulation

Page 37: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

LTP as a Neural Mechanism of Learning and Memory Consistent with the synaptic changes

hypothesized by HebbLTP can last for many weeks.LTP only occurs if presynaptic firing is

followed by postsynaptic firing Hebb’s postulate for learning

Co-occurrence is necessary for learning and memory

Page 38: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

LTP as a Neural Mechanism of Learning and Memory Elicited by levels of stimulation that mimic

normal neural activity LTP effects greatest in brain areas

involved in learning and memory Learning can produce LTP-like changes Drugs that impact learning often have

parallel effects on LTP

Page 39: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

LTP as a Neural Mechanism of Learning and Memory Much indirect evidence supports a

role for LTP in learning and memory LTP can be viewed as a three-part

process:Induction (learning)Maintenance (memory)Expression (recall)

Page 40: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Induction of LTP: Learning

Usually studied where NMDA glutamate receptors are prominent

NMDA receptors do not respond maximally unless glutamate binds and the neuron is already depolarized

Calcium channels do not open fully unless both conditions are met

Page 41: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Induction of LTP: Learning

Calcium influx only occurs if there is the co-occurrence that is needed for LTP, leading to the binding of glutamate at an NMDA receptor that is already depolarized

Calcium influx may activate protein kinases that induces changes causing LTP

Page 42: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Maintenance and Expression of LTP: Storage and Recall Pre- and postsynaptic changes LTP is only seen in synapses where it

was induced Protein-synthesis underlies long-term

changes Long-lasting changes in extracellular

glutamate levels

Page 43: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

Maintenance and Expression of LTP: Storage and Recall How are presynaptic and postsynaptic

changes coordinated? Nitric oxide synthesized in postsynaptic

neurons in response to calcium influx may diffuse back to presynaptic neurons

Structural changes are now a well-established consequence of LTP

Page 44: Pinel basics ch09

Copyright © 2007 by Allyn and Bacon

LTP – A Final Note

Most LTP research has focused on NMDA-receptor-mediated LTP in the hippocampus, but LTP is mediated by different mechanisms elsewhere.

LTD, long-term depression, also exists

Why should there be a variety of mechanisms and places that underlie learning and memory?


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