THE MAGNETIC COUNTERPART OF THE CONTINGENT NEGATIVE-VARIATION

The magnetic counterpart of the CNV, the contingent magnetic variation (CMV), was investigated in an Go/No Go design: subjects moved their i ndex finger to the offset of a 4 sec tone of a certain frequency in th e Go condition and were asked not to move during presentation of a 4 s ec tone of different frequency in the No Go condition. During the prep aratory interval, both the CMV and the electrical wave form followed a similar time course and both produced an equally pronounced statistic al difference between conditions (Go and No Go). Compared to the varia bility in the auditory evoked fields, the CMV showed considerably more variance in the field distribution across subjects. The polarity reve rsal across the temporal surface of the head and the pronounced amplit udes over inferior temporal areas led us to conclude that a significan t temporal activity contributes to both the late and the early CMV. Ho wever, neither for the early nor for the late CMV component did a sing le equivalent dipole prove to be a satisfying model. The data are cons istent with the suggestion that the earlier as well as the later aspec ts of the CMV are fed through distributed sources in motoric, sensory and association areas, a distribution with considerable intersubject v ariability.