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Abstract:
To test among hypotheses of prefrontal function, we have
developed a collection of tasks that permits various cognitive
demands (e.g. memory, response inhibition) to be independently
varied. Tasks were of comparable difficulty, as indicated by
response times and accuracy for both children and adults. Last year
we reported on the first of these tasks. A target appeared to the
left or right of a fixation point; subjects pushed a button on the
same or opposite side of the target depending upon the target's
identity. This task, which required both the inhibition of a
prepotent response (always pushing on the same side as the target)
and the need to remember arbitrary response rules (same or opposite
sides) yielded clear dorsolateral prefrontal cortex (DLPFC;
Brodmann Areas 9/46) activation. Now we report on new tasks that
vary memory and inhibition requirements. When memory load is
reduced (by using arrows to indicate where the subject should
respond, instead of memorized rules), DLPFC shows little or no
activation. When memory load is increased (by increasing the number
of memorized rules) DLPFC activation is still found, whether or not
a spatially prepotent response must be inhibited (by varying the
location of the targets).
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