The present report studied the contingent negative variation during Gap and Non-Gap conditions using visual stimulation and manual responses. The reaction times during the Gap condition were facilitated compared with those of the Non-Gap condition. The contingent negative variation component was obtained during the preparatory period from electrodes placed at 58 scalp sites for both Gap and Non-Gap conditions. The comparison between both conditions: Gap and non-gap did not show statistically significant differences during the preparatory period. The topography of the voltage and current source density maps showed three different foci: (i) an early negativity centred in electrodes overlying the supplementary motor area and cingulate motor areas, (ii) an activation over the primary motor cortex contralateral to the finger movement, and (iii) a bilateral activation on posterior sites. All these results suggest that the facilitation induced by the warning stimuli occurs in neural circuits that would be recruited for the subsequent processing of the imperative stimulus. The facilitation of the reaction times during the gap condition with respect to non-gap condition must be justified by neural events occurring during the gap period.