Frontal hemispheric differences in the Bereitschaftspotential associated with writing and drawing.

Abstract

Twenty right-handed subjects participated in a study investigating the cerebral potentials related to three complex actions: (1) writing one's own signature, (2) drawing a pentagram, and (3) fast meaningless scribbling. The Bereitschaftspotential (BP, readiness potential) started as early as 3 s prior to writing, 2.5 s prior to drawing, but only 1.5 s prior to scribbling. In all three tasks, the BP had its earliest onset over the supplementary motor area (SMA). BP topography was shifted towards the frontal lobes when compared to encephalographic activity reflecting simple finger movements, and was very weak in retro-rolandic leads. The side of the performing hand, as assessed from scribbling, was reflected in a contralateral preponderance of the precentral BP. The maximum BP (about 6 microV) was, in all three tasks, located in FCz (mid fronto-central) overlying the SMA. This location is different from that for simple finger movements, when the maximum is at the vertex. Hemispheric differences were found over the frontal cortex and were characteristic for the verbal and spatial tasks involved: for writing, the BP was significantly larger left frontally than right (even after considering the effect of the performing hand from scribbling), and the difference was largest prior to the onset of movement; for drawing, the BP was larger over the right than over the left frontal lobe, and the difference was largest during the movement.