Transcript His conclusion: equipotentiality

Chapter 11
Learning, Memory, and Amnesia
How Your Brain Stores
Information
Copyright © 2009 Allyn & Bacon
Studying Memory
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Neuroscientists
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Psychophysiologists
Behavioral Paradigms
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Morris Water Maze
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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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Generally accepted
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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
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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
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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
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Let us assume that the persistence or
repetition of a reverberatory activity (or
"trace") tends to induce lasting cellular
changes that add to its stability.... When an
axon of cell A is near enough to excite a
cell B and repeatedly or persistently takes
part in firing it, some growth process or
metabolic change takes place in one or both
cells such that A's efficiency, as one of the
cells firing B, is increased.
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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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Long-term Potentiation (LTP)
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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
Memories are thought to be encoded by
modification
of ©synaptic
strength
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2009 Allyn & Bacon
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Enhancement in signal transmission
between two neurons that results from
stimulating them synchroniously
Enhanced communication between preand post synaptic
neuronsimprovement in postsyn. To
receive signals from pre
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Increasing activity of receptors and number
of receptors
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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
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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
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Durbach (2000)
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Two changes in brain
1) Internal structure of neurons around
area of synapse
2)Increase in number of synapses
between neurons
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Next Class
Stress and the Brain
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