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Abstract:
Employing an FMRI version of the "oddball" task, we
demonstrated activation of the dorsolateral prefrontal cortex
(DLPFC) to Targets in healthy subjects but not schizophrenic
patients, while infrequent non-target Novel stimuli activated
inferior frontal cortex in schizophrenia patients only. We
hypothesized that schizophrenic patients were distracted by the
novel stimuli that interfered with their selection of
task-appropriate targets. Here we assess the role of attention and
stimulus salience on the inferior frontal activation in
schizophrenic patients using fMRI, and the Target and Novelty
associated N2/P3 ERP responses. Healthy (11) and schizophrenic (12)
subjects viewed a series of centrally displayed squares (1/1.5 s)
and circles (3-5% of trials per run), with bilateral flankers of
either squares (95%) or pictures of everyday objects (3-5%).
Subjects made a 2-button choice-RT response to the circles and
squares, and ignored all peripheral stimuli. EPI of 8 axial slices
we! re acquired on a 1.5 T MR system. Epochs surrounding each
target and novel picture were excised and the time course of each
voxel was convolved with the expected hemodynamic response
function. Healthy subjects showed DLPFC activation to Targets, as
well as N2/P300. Schizophrenic patients showed no DLPFC activation
and abnormal N2/P3s to Targets, along with IFG activation to
Novels, indicative of executive dysfunction.
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