Temporo-Spatial Dynamics of Event-Related EEG Beta Activity during the Initial Contingent Negative Variation

In the electroencephalogram (EEG), early anticipatory processes are accompanied by a slow negative potential, the initial contingent negative variation (iCNV), occurring between 500 and 1500 ms after cue onset over prefrontal cortical regions in tasks with cue-target intervals of about 3 s or longer. However, the temporal sequence of the distributed cortical activity contributing to iCNV generation remains unclear. During iCNV generation, selectively enhanced low-beta activity has been reported. Here we studied the temporal order of activation foci in cortical regions assumed to underlie iCNV generation using source reconstruction of low-beta (13–18 Hz) activity. During the iCNV, elicited by a cued simple reaction-time task, low-beta power peaked first (750 ms after cue onset) in anterior frontal and limbic regions and last (140 ms later) in posterior areas. This activity occurred 3300 ms before target onset and provides evidence for the temporally ordered involvement of both cognitive-control and motor-preparation processes already at early stages during the preparation for speeded action

Relationship between Dexamethasone Suppression Test and Contingent Negative Variation in Major Depressive Patients

We tried to relate two different indexes sensitive to the perturbations induced by major depression: the Dexamethasone Suppression Test or DST (Caroll, 1982) and the Contingent Negative Variation (CNV). The question was whether abnormalities in cortisol levels, following dexamethasone would enlight the modifications observed in CNV parameters and other electrophysiological indexes (EEG spectrum, reaction time). In 61 major depressive patients, 29 being DST-non-suppressors, we calculated differences in electrophysiological variables according to DST suppression or not, but we were not able to evidence significant differences between the groups. However, there were correlations between log-transformed levels of cortisol and on the one hand, CNV slope (r = -0.34, P less than 0.03) and on the other hand, reaction time (r = 0.45, P less than 0.01). Correlations between electrophysiological variables appeared in the sole suppressors group (e.g. CNV amplitude and alpha rythm reactivity; post-imperative variation and percent beta of the EEG spectrum). These results underline the complementary aspect of the two methods

Contingent negative variation and severity of depression

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Etude des modifications de l'EEG quantifié et de la VCN au cours de l'inhalation de protoxyde d'azote

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