STEADY-STATE VISUALLY EVOKED-POTENTIAL TOPOGRAPHY DURING THE WISCONSIN CARD SORTING TEST

This paper describes, for the first time, changes in steady-state visually evoked potential (SSVEP) topography associated with the performance of a computerised version of the Wisconsin card sort test (WCS). The SSVEP was recorded from 64 scalp sites and was elicited by a 13 Hz spatially uniform visual flicker presented continuously while 16 subjects performed the WCS. In the WCS, the sort criterion was automatically changed after subjects had sorted 10 cards correctly. Feedback on the 11th card always constituted a cue for a change in the sort criterion. It was found that in the 1-2 sec interval after the occurrence of the cue to change sort criterion, the prefrontal, central and right parieto-temporal regions showed a pronounced attenuation in SSVEP amplitude and an increase in phase lag. These changes, interpreted as an increase in regional cortical activity, are not apparent in the equivalent portions of the WCS when the sort criterion does not need to be changed. These results indicate that the levels of prefrontal and right parieto-temporal activity varied during the performance of the WCS, peaking at the times a change in sort criterion was required.