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Memory Systems
Chapter 23
Friday, December 5, 2003
What is Memory?
Memory is a change in the synapses of the
neurons comprising a network.
 Memories are not static “records” but
products of a change in the connections
among nerve cells.
 Memories extract and store the meanings of
events, not their exact details.

Sensory aspects are reexperienced not recalled.
 Recall is reconstructed, not just retrieved.

The Search for the Engram
Engram – the physical memory trace.
 Lashley couldn’t find one:

“This series of experiments…has discovered
nothing directly of the real nature of the engram.
I sometimes feel in reviewing the evidence on
the localization of the memory trace, that the
necessary conclusion is that learning just is not
possible.”
pg 276 of text
Where is Memory?
Both cortical and subcortical structures are
involved in creating memories.
 Although memories appear to be stored in the
cortex, they are:

Distributed – spread out in a network
 Redundant – represented in multiple ways


Hebbian cell assemblies (loops) permit access
at various points in a network.
Stages of Memory

Sensory buffers – one for each sense:
Iconic – for visual information
 Echoic – for auditory information


Working memory/short term memory:
Limited capacity – 7 plus or minus 2
 Capacity can be expanded by chunking
 Executive functions


Long term memory – permanent.
Amnesia
Retrograde amnesia – inability to recall
previously stored memories of one’s life.
 Anterograde amnesia – inability to form new
memories of events in one’s life.



H.M. -- surgery removed parts of the temporal
lobe, including hippocampus.
With amnesia, some kinds of memory are
spared, others impaired, suggesting there are
different kinds of memory.
Working Memory
Unimpaired in amnesics.
 In humans, localized to frontal lobes.
 Delayed development of frontal lobes in
humans and monkeys:

“A not B” task
 Can’t tolerate delays (8-10 sec) until
1-1/2 yrs old

Infantile Amnesia

Inability to remember events of one’s
childhood before ages 3-4.
10 year olds couldn’t remember preschool
classmates
 Attributed to immaturity of memory systems in
children.

Long Term Memory

Localized to temporal lobes:
Hippocampus – memory formation and
consolidation
 Entorhinal cortex (adjacent to hippocampus)


During memory storage the temporal region
forms a connection between the relevant
networked areas of the brain.
Procedural vs Declarative
Procedural memory – memory for how to do
things, skills.
 Declarative memory – memory for abstract
knowledge, facts and events of one’s life.
 Only memory for events of one’s life is
affected by amnesia – not procedural memory
or memory for facts.

Explicit vs Implicit

Implicit memory – does not involve conscious
awareness – unimpaired in amnesics.





Procedural memory
Priming, recognition tasks
Classical conditioning, habituation
Semantic memory
Explicit memory – involves conscious attention –
impaired in amnesics.

Episodic and autobiographical memory, recall
Conditioning

A form of learning:
Classical (Pavlovian) conditioning – present at
birth, unimpaired in amnesics.
 Operant (instrumental) conditioning.


How are learned associations maintained?

Amygdala (and emotional arousal) mediates
activity of the hippocampus to form neural
connections.
Types of Amnesia
Damage to Temporal Lobe – H.M.
 Damage to Thalamic Structures – N.A.



Most impaired with verbal material.
Korsakoff’s Syndrome
Chronic alcoholics with thiamine deficiency
 Retrograde and anterograde amnesia.


Electroconvulsive Shock Therapy (ECT)
Amnesia and Forgetting

Forget at normal rate – thalamic (diencephalon):

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
N.A.
Korsakoff’s patients
Monkeys with medial thalamic lesions
Forget rapidly – hippocampus:

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H.M.
Bilateral ECT
Monkeys with amygdala/hippocampus lesions
Semantic Memory

Unimpaired by anterograde amnesia.
Children with amnesia develop normal semantic
memory.
 Intact entorhinal cortex may be used to store
semantic memories despite hippocampal damage.


Context-rich, episodic memory impaired.
Cellular Mechanisms

Habituation involved suppression of action
potentials through decreased release of
neurotransmitter – change is at the synapse.


Sensitization – increased neurotransmitter release
Explicit memory involves long-term
potentiation, LTP (a physical change to
neurons) in hippocampus and neocortex.

See Chapter 24 for details