Neuromagnetic localization of the late component of the contingent negative variation.

The contingent negative variation (CNV) in a warned choice reaction time task was studied in 24 healthy subjects by use of magnetoencephalography (MEG). Special interest was focused on the late component of the CNV, CNVL. Source localization of the magnetically recorded CNVL, mCNVL was performed on 13 subjects, selected on the basis of the strength and stationarity of the electrically recorded CNV, eCNVL. To achieve whole head mapping, up to 500 epochs from different scalp positions were recorded, including a pretrial learning period of 40 epochs. The neuromagnetic signals studied in this experimental protocol are thus related to neurological processes that are present after an initial learning period has occurred. In 11 subjects, a goodness of fit between 88% and 95% was achieved using a two-dipole model with one equivalent source localized close to the precentral cortex contralateral to the side of movement, at mean a depth of 30 mm. Estimates of ipsilateral equivalent sources were less consistent across subjects. In 9 subjects the estimated ipsilateral sources were located symmetrically to the contralateral source. The results of this study suggest that the dominant source of the mCNVL is located near the bottom of the sulcus precentralis at the anterior bank of the gyrus precentralis, close to the sulcus frontalis superior. This supports previous findings that the CNVL is closely related to the readiness potential, and that the major cortical activity is symmetrically located in the left and right premotor areas.