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Abstract:
Learning associations between stimuli is commonly considered
a function of the hippocampal formation (HF). Consistent with this
suggestion, we have recently observed impaired associative learning
(AL) test performance in older people with progressively worsening
cognitive function and proposed HF atrophy. Recent research
suggests that other brain regions (including the amygdala and the
orbito-frontal cortex) may also be involved in AL when the stimuli
to be associated have some emotional or motivational significance.
We measured the performance of a group of older people with
declining cognitive function on a series of AL tasks to determine
the conditions under which they displayed impaired performance, and
to determine whether their AL impairments were derived from HF
atrophy or damage to other brain regions. Our experimental
protocols were guided by a computational model of HF function in AL
described by Gluck and Myers (1997) and by a theory of AL described
by Rolls (2000). Older people with declining cognitive function
displayed impaired performance on tasks designed to isolate the HF,
but normal performance on an AL task in which the stimuli presented
may have also been processed by brain regions other than the HF.
These results constrain current theories of HF involvement in AL,
and provide confirmatory evidence that the HF is damaged in older
people with mild cognitive impairments.
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