Transcript His conclusion: equipotentiality

Chapter 11
Learning, Memory, and Amnesia
How Your Brain Stores
Information
Copyright © 2009 Allyn & Bacon
Brain Mechanisms in Memory
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Engram: physical representation of
memory in brain
Karl Lashley (1929)- earliest
psychologists to study
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Believed memory stored in association
cortex
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Performed series of lesion
Deficit related to size of lesion, not location
His conclusion: equipotentiality
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Localization of Memory
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Penfield (1958)-stimulation in parts of
temporal lobe produced specific
memories in human patients; flawed
because could’ve been related to
seizures
Sparked interest in Temporal lobes in
role of formation and retention of longterm memories
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Temporal lobe and Memory
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Patients w/ anterograde amnesia (deficit
in ability to form NEW memories)
Case Study: HM
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Accident led to seizures bilaterial
removal of temp lobes (hippo, amygdala, &
some assoc cortex)
Seizures improved; IQ, personality, skills
unchanged, earlier memories intact
Suffered anterograde amnesia
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Amnesic Effects of Bilateral
Medial Temporal Lobectomy
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H.M. – an epileptic who had his
temporal lobes removed in 1953
His seizures were dramatically reduced
– but so was his long-term memory
Mild retrograde amnesia and severe
anterograde amnesia
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Tissues
typically
excised in
medial
temporal
lobectomy
Copyright © 2009 Allyn & Bacon
Copyright © 2009 Allyn & Bacon
Conclusions from HM studies
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Aspects of memory managed by diff
parts of brain
Damage to medial temp lobesaffects
explicit NOT implicit memories
Not affect LTM, but does affect transfer
of STM to LTM
Copyright © 2009 Allyn & Bacon
Copyright © 2009 Allyn & Bacon
Amnesia
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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 (LTM), his
short-term memory (STM) is intact
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Where Are Memories Stored?
Each memory is stored diffusely throughout
the brain structures that were involved in
its formation
 Hippocampus – spatial location
 Perirhinal cortex – object recognition
 Mediodorsal nucleus – Korsakoff’s
 Basal forebrain – Alzheimer’s disease
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Where Are Memories Stored?
(continued)
Damage to a variety of structures results in
memory deficits
 Inferotemporal cortex – visual perception of
objects – changes in activity seen with
visual recall
 Amygdala – processes emotional
memories
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Where Are Memories Stored?
(continued)
Damage to a variety of structures results in
memory deficits (continued)
 Prefrontal cortex
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Temporal order of events and working memory
Different part of prefrontal cortex may mediate
different types of working memory – some
evidence from functional brain imaging studies
Copyright © 2009 Allyn & Bacon
Synaptic Mechanisms of
Learning and Memory
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What is happening within the brain
structures involved in memory?
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Hebb – changes in synaptic efficiency are the
basis of LTM
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Repeated stimulation of neural circuits
Long-term potentiation (LTP) – synapses are
effectively made stronger by repeated
stimulation
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Bliss & Lomo (1973)
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Rapid series of electrical shocks to
hippo pathway increases PSPs in target
cells.
Experience makes these synapses
more efficient
Change in responsiveness in target
cells called LTP
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Long-Term Potentiation (LTP)
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LTP is consistent with the synaptic
changes hypothesized by Hebb
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LTP can last for many weeks
LTP only occurs if presynaptic firing is followed
by postsynaptic firing
Hebb’s postulate for learning
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Co-occurrence of firings in pre- and
postsynaptic neurons necessary for learning
and memory
Copyright © 2009 Allyn & Bacon
LTP as a Neural Mechanism
of Learning and Memory
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Elicited by high frequency electrical
stimulation of presynaptic neuron;
mimics normal neural activity
LTP effects are greatest in brain areas
involved in learning and memory
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Structural Changes from LTP
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Increase in number and size of
synapses
Increase in number and size of
postsynaptic spines
Changes in the pre-and post-synaptic
membranes
Copyright © 2009 Allyn & Bacon