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Abstract:
Two competing theories of the contribution of the anterior
cingulate cortex (ACC) to executive processes have been
articulated. The first, based upon studies showing ACC activation
when executive processes are engaged, proposes the ACC implements
the strategic allocation of attention. The second, based upon ERP
and fMRI studies of error-related activity, suggests the ACC serves
an evaluative function, reflecting the need to engage strategic
processes. Using event-related fMRI we tested these two hypotheses,
using a Stroop task which manipulated strategic processes. High
Control blocks were mostly incongruent (e.g. the word RED in blue),
Low Control mostly congruent (e.g. the word RED in red).
Performance data confirmed that during the High Control condition,
strategic processes were engaged, and response competition reduced
(39 msec Stroop effect). During the Low Control condition,
strategic processes were less engaged and response competition
increased (198 msec Stroop effect). Transient, response related ACC
activity, greater for incongruent than congruent trials, was
present in the Low Control, high competition condition, but not in
the High Control, low competition condition. This is inconsistent
with the hypothesis that the ACC implements strategic processes to
reduce competition. Instead it suggests that the ACC serves an
evaluative function, detecting cognitive states such as response
competition, and representing the knowledge that strategic
processes need to be engaged.
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