Hemispheric differences in VEP elicited by mental arithmetic and tachistoscopically presented spatial transformation tasks.

Recent studies have furnished evidence of hemispheric asymmetry in the EEG and event-related potentials in man. Face-validated tasks as verbal and nonverbal ones (A: mental arithmetic; B: detection of a target in the hand of a manikin in different positions) were tachistoscopically presented to check side differences of VEP parameters in 5 healthy right-handed subjects. The EEG was recorded from C3, C4, P3 and P4 referenced to linked ears. The mean peak latencies of averaged VEPs were P1: 107 ms, N1: 142 ms, P2: 203 ms, N2: 265 ms, P3: 357 ms. No consistent treatment effects were obtained for peak latencies. Regardless of side differences, the attention related VEP amplitudes P1-N1 and N1-P2 were higher in A. Rightleft differences were found to be higher for visual-spatial transformation, except P2-N2 amplitude. The asymmetry of amplitudes suggests a higher activity of the right hemisphere in B. A possible description of dynamic variations due to learning and changes of strategy during repetitive mental activity by means of changes in EP asymmetry will be of interest for further investigations.