Transcript Medial Temporal Lobe Activity during Retrieval of Semantic Memory

Medial Temporal Lobe Activity during
Retrieval of Semantic Memory Is
Related to the Age of the Memory
Christine N. Smith1
and Larry R. Squire
Reporter：Yi Jing Jiang
Assistant：Han Yuan Lai
Memory
• Medial temporal lobe
▫ hippocampal region (CA fields, dentate gyrus, and
subicular complex) and the adjacent perirhinal,
entorhinal, and parahippocampal cortices(Larry et
al., 2004)
• Amnesia
▫ Damage in hippocampus
• Two theory of time-dependent memory
▫ Standard consolidation theory / Multiple trace
theory
Standard consolidation theory
• The hippocampus is essential for a specific kind
of memory, here termed declarative memory
• The hippocampus is needed temporarily to bind
together distributed sites in neocortex that
together represent a whole memory(Squire, 1992)
Multiple Trace Theory
• Hippocampus and related structures are
involved in certain forms of memory(e.g.
autobiographical episodic and spatial
memory)(Lynn& Morris, 1997)
• Using more sensitive measures than previously
the case , patients with temporal lobe damage
show deficits in both episodic and spatial detail
that can bed observed even for very remote
memories (Nadel et al.,2000)
(Katherine et al., 2009)
Introduction
• Recent memory and remote memory
• Mix of the consequences
• Study of recent and remote memory with
neuroimaging presents a number of challenges
▫ Encoding
▫ Vividness or richness
▫ Episodic recollections
Introduction
• Looked for regions that exhibited gradually
decreasing activity as participants recalled
memories from recent memories, a constant
level of activity during recall of more remote
memories and the opposite pattern.
• Directly evaluating the effect of memory age
independently of the success of encoding the test
questions , richness and episodic recollection.
Materials and Methods
• Participants
▫ 15 healthy participants
• Background
▫ The fate of old memories after medial temporal
lobe damage(Bayley et al., 2006).
• Materials and Procedure
▫ News Event Test
▫ Subsequent memory for the content of the news
event questions
▫ Recall accuracy
▫ Richness
▫ Episodic memory
• fMRI parameters and analysis
▫ ANFI
▫ Covariance analysis
Result
• Recall accuracy
▫ Related to how long ago the
event occurred (linear trend,
F(1,14) 13.9, p<0.01)
• Subsequent memory for the
content of the news event
questions
▫ 88.9+2.0% correct
▫ Unrelated to how long ago the
news events occurred ( p>0.20)
Result
• Richness
▫ Ratings and number of facts
didn’t relate to how long ago
the event occurred ( p>0.30)
• Episodic memory
▫ In association with 20.6% of
the correctly answered
▫ Unrelated to how long ago
the news events occurred
( p>0.50)
Result-fMRI findings(Time period)
REC>REM： Linearly decreasing activity across the
four most recent time periods
(1–12 years),
and adecreased
REC>REM
: Linearly
constant level of activity across
more
remote
time
across
all time
periods.
periods (13–30 years)
REM>REC：Linearly increasing
activity across the four most recent
time periods (1–12 years), and a
constant level of activity across
more remote time periods (13–30
years)
Result-fMRI findings(Encoding)
Activity associated with questions whose
content was subsequently remembered
was compared with activity associated
with questions whose content was
subsequently forgotten.
Discussion
• Regions in the hippocampus, amygdala, and
temporopolar cortex in which activity during
recall related to the age of the memory
▫ Hippocampus has a time-limited role in the
formation and maintenance of memory
• There were no regions with this pattern of
activity in the medial temporal lobe, but regions
in the frontal, lateral temporal, and parietal
cortex did exhibit increases in activity that were
related to the age of the memory.
Discussion
• Correctly answered questions were more
frequent
• Earlier studies may not have measured memory
from a sufficient number of time periods in the
recent past
• The regions in the medial temporal lobe that
responded during recall according to the age of
the memory were different from subsequent
memory
• The findings appear to be due to a decreased
dependence on medial temporal lobe structures
as time passes after learning
Issue
• Design a experiment to demonstrate the same
effect without News Event Test
• What is pattern of the age of the memory as
retrieval of episodic memory
• What is the relationship between subsequent
memory and the age of the memory
• How to measure the age of the memory from
implicit memory
Reference
• Akers KG, Frankland PW (2009) Grading Gradients: Evaluating Evidence for Time
dependent Memory Reorganization in Experimental Animals. Journal of
Experimental Neuroscience 2009:2 13–22.
• Bayley PJ, Hopkins RO, Squire LR (2006) The fate of old memories after medial
temporal lobe damage. J Neurosci 26:13311–13317.
• Nadel L, Moscovitch M (1997) Memory consolidation, retrograde amnesia and the
hippocampal complex. Curr Opin Neurobiol. 1997;7:217–27.
• Nadel L, Samsonovich A, Ryan L, Moscovitch M (2000) Multiple Trace Theory of
Human Memory: Computational, Neuroimaging, and Neuropsychological Results.
HIPPOCAMPUS 10:352–368
• Squre LR (1992) Memory and the Hippocampus: A Synthesis From Findings With
Rats, Monkeys, and Humans. Psychological Review Vol. 99, No. 2,195-231
• Squire LR, Stark CEL, Clark RE (2004) The Medial Temporal Lobe. Annu. Rev.
Neurosci 27:279–306.
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