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Abstract:
It has been proposed that dorsolateral prefrontal cortex
(DLPFC) is involved in inhibitory cognitive operations (e.g.,
Diamond, 1985), and further, that inhibitory processing is a
fundamental mechanism mediating cognitive aging (e.g. Hasher,
1988). Verbal working memory (WM) tasks may require inhibitory
processes when: 1) The contents of WM must be deleted before
additional information can be stored, and 2) Prepotent responses
must be suppressed in order for a correct response to be made. We
provide evidence for these proposals by using PET to compare two
item recognition tasks. For both tasks, a memory set of four
letters was presented on each trial. In the low-overlap (LO) task,
no letter appeared in either the target set or as the probe more
than once every three trials. In the high-overlap (HI) task, half
of the letters in each set overlapped with the set from the
preceding trial. Thus, in the HI task, half the probes that
required a "No" response had recently been presented; presumably,
subjects had to inhibit a "Yes" response to such "recent
negatives". In the HI-LO subtraction, a reliable area of activation
was found in left DLPFC in younger, but not senior, adults.
Furthermore, seniors were disproportionately slower and less
accurate in responding to recent negatives than to other kinds of
negative probes. These results suggest that older adults lack the
prefrontal resources to inhibit their reactions to the recent
negatives.
Supported by NIA (AG 13027).
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