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 index finger to the offset of a 4 sec tone of a certain frequency in the Go condition and were asked not to move during presentation of a 4 sec tone of different frequency in the No Go condition. During the preparatory interval, both the CMV and the electrical wave form followed a similar time course and both produced an equally pronounced statistical difference between conditions (Go and No Go). Compared to the variability in the auditory evoked fields, the CMV showed considerably more variance in the field distribution across subjects. The polarity reversal across the temporal surface of the head and the pronounced amplitudes over inferior temporal areas led us to conclude that a significant temporal activity contributes to both the late and the early CMV. However, neither for the early nor for the late CMV component did a single equivalent dipole prove to be a satisfying model. The data are consistent with the suggestion that the earlier as well as the later aspects of the CMV are fed through distributed sources in motoric, sensory and association areas, a distribution with considerable intersubject variability.