Intracerebral recordings of slow potentials in a contingent negative variation paradigm: an exploration in epileptic patients.

While exploring epileptic patients with intracerebral multilead electrodes, we applied a forewarned reaction time task with two successive sound stimuli, a paradigm that is known to elicit a contingent negative variation (CNV). The second, imperative sound stimulus was followed by a hand or a foot movement. Eleven patients suffering drug-resistant partial epilepsies were tested. The slow potentials developing during the time between the two stimuli were usually not typical CNVs (sometimes comprising multiple successive components with distinct polarities). Such "CNV-like" potentials were obtained from two main cortical zones: a central one including premotor, motor, supplementary motor, postcentral and cingulate areas; and a temporal zone, mainly including the auditory cortex and its vicinity, and in some cases the amygdala. This restricted localization contrasted with the broader extent of the CNVs on the scalp. Intracerebral CNV-like events were obtained from both hemispheres, independent of the side of the performed movement. In some patients, readiness potentials (RPs) were also recorded for comparison and displayed a more restricted extent, being present only on the contralateral motor cortex and bilaterally in the supplementary motor areas. Our data suggest that the last part of the CNV cannot just be identified with the RP.