long term memory with a focus on neural...
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LONG TERM MEMORY with a focus on neural mechanisms
Long-term memory covers a span that stretches from about 30 seconds ago to your earliest memories. Thus, all of this person’s memories, except the memory “I just sat down,” would be classified as long-term memories.
Long Term Memory
Memories are distributed
• Where is memories stored in the brain? – in the same areas that processed the original event.
Kinds of Memory
08‐24
W. W. Norton
Patient H.M.
Effects of Bilateral Medial Temporal Lobectomy
• H.M. – an epileptic who had large sections of medial temporal lobes removed in 1953
• His seizures were dramatically reduced – but so was his memory
Amnesia
• Retrograde (backward‐acting) – unable to remember the past
• Anterograde (forward‐acting) – unable to form new memories
H.M.’s amnesia
• Cannot recognize himself in a recent photograph (years after surgery)
• Cannot recognize psychologist Brenda Milner after 100’s of visits
• 1 hour after dinner, he has forgotten what he ate, or even that he has eaten.
• … but he can recall facts and events from his life before surgery, with some weakness for events just prior to surgery.
Double Dissociation of STM and LTM
08‐10
Drachman, D
.A., and Arbit, J., M
emory and the hipp
ocam
pal com
plex. II. Is m
emory a multip
le process?,
Archives of Neu
rology 15 (196
6): 52–61
.
Ask H.M to remember “584”
• “It’s easy. You just remember 8. You see 5, 8, and 4 add to 17. You remember 8, subtract it from 17 and it leaves 9. Divide 9 in half and you get 5 and 4 and there you are: 584. Easy.”
• Two minutes later, after distraction by another task, he has forgotten the number as well as his strategy.
H.M. learns mirror‐tracing task
Implicit procedural memory in amnesia (and normals)
• Gollins partial pictures test.
• 20 items, fragments to full drawings
• H.M. (and other amnesiacs) do better on a re‐test given one hour later.
08‐20
implicit perceptual memory (test=priming) vs.
explicit memory (test=recognition) in NORMALS
Fig.6‐10,p.194
Different decay functions for Explicit and implicit memory
08‐17b
Tulving, E., Gordo
n Hayman, C.A., and MacDon
ald, C.A., Long‐la
sting pe
rcep
tual priming and semantic
learning in amne
sia. A case expe
rimen
t, Jo
urnal of E
xperim
ental Psychology 17
(199
1): 595
–617
. Cop
yright
© 199
1 by th
e American Psychological Associatio
n. Adapted
with
permission
.
Semantic Priming in amnesia
(Patient K.C, who has severe retrograde and anterograde amnesia following motorcycle accident and MTL damage)
Semantic memory in H.M.?
• H.M.’s drawings of a house he inhabited 1958‐1974
• (owner later knocked down a wall)
Kinds of Memory
How/Why do amnesiacs remember the past (before their brain damage)?
• Memory undergoes a process of consolidation
Memory consolidation affected by electroconvulsive therapy
Squire et al (1983) • Studied patients’ memory for details of TV shows that ran for 1 season (no re‐runs)
• Before therapy – Memory better for recent shows
• After therapy – Memory better for earlier shows
08‐15
Adapted from Squire, L.R., and Slater, P., Electroconvulsive therapy and complaints of memory dysfunction: A prospective three‐year follow‐up study, British Journal of Psychiatry 142 (1983): 1–8.
Amnesia after electroconvulsive therapy illustrates memory consolidation
Hippocampus is a convergence area: receives input from, and sends output to, all of cortex.
W. W. Norton
Entorhinal cortex
Perirhinal cortex Parahippocampal cortex
The Standard model of System Consolidation: first Hippocampus, then Cortex, mediates memories
Standard model of consolidation • Memories change from fragile to robust
• At first, hippocampus is critical • Recapitulation: when we retrieve memories, we reinstate the
pattern of activations present during encoding, and strengthen and adjust neural connections
• Later, (widely distributed) cortex is the site of storage. Hippocampus stops being critical
• Newer views agree with the stronger, more robust contribution of cortex over time but differ on why this is…