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Abstract:
We report results from an event-related fMRI experiment using
an ambiguous visual stimulus to investigate voluntary control. 6
healthy male volunteers watched the image, pressing a key whenever
interpretation changed. In condition P, the stimulus was watched
passively. During active switching (SW), subjects voluntarily
induced a change of perception, and in active suppression (SU), the
task was to voluntarily prevent such shifts. Fast 3D multi-shot
spiral imaging data were analyzed in SPM97. Event-related blood
flow was modeled with a synthetic hemodynamic response function.
Evoked activity during the voluntary conditions was compared to P.
During AS, significantly greater activation than in P was found in
orbitopolar frontal lobe bilaterally. In SU, the left fusiform
gyrus showed significantly more evoked activity. Regional
activities in these areas were highly correlated in both SU and AS,
but not during P. Volition was thus is characterized by
modality-specific frontal-posterior interactions, volitional acts
corresponding to phasic frontal activity. The degree of
modality-specific coupling was associated with right dorsolateral
prefrontal cortex (DLPFC) activation. This confirms a key role of
this area in volition, and suggests a mechanistic account of other
high-level functions subserved by the DLPFC.
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