Inter-hemispheric lateralization of event related potentials; motoric versus non-motoric cortical activity

To study hemispheric lateralization of cortical potentials associated with motoric and non-motoric function, cortical activity was recorded accompanying either finger extension or saccadic eye movements in a contingent negative variation (CNV) paradigm. Subjects viewed computer-generated pacing stimuli, presented in the left visual hemi-field, and were instructed to either initiate or inhibit a motor response following an imperative signal. Motoric lateralization was assessed by means of the lateralized readiness potential (LRP). In addition, a measure complementary to the LRP was introduced to investigate non-motoric lateralization (NML). Contralateral inter-hemispheric lateralization was evident in the LRP preceding finger movement, but was absent prior to eye movements. However, pre-saccadic cortical response profiles did exhibit a right hemispheric, non-motoric lateralization (NML) during stimulus presentation. Comparable non-motoric lateralization was found for finger extension. Results of the present study suggest that non-motoric lateralization may be a contributing factor to the frequently reported inter-hemispheric asymmetry preceding self-initiated saccadic eye movements. Results of the present study also suggest that the latter may be related to a covert shift of visuospatial attention toward the saccadic target. Associated shifts of attention are suppressed in a CNV paradigm, where attentional focus is primarily on the CNV stimulus during the pre-saccade period.