Posterior and anterior contribution of hand-movement preparation to late CNV.

The late part of the Contingent Negative Variation (CNV) is assumed to be a composite potential, reflecting both movement preparation and several other processes. To assess the contribution of hand–motor preparation to overall CNV, 3 S1–S2 experiments were performed. Replicating earlier results that have been interpreted as demonstrating hand–motor preparation, Exp 1 showed that CNV gets larger centro–parietally under speed instruction. Exps 2 and 3 compared preparation for hand responses to preparation for ocular responses varying the effector system either between blocks (Exp 2) or between trials (Exp 3) and also comparing these preparation situations to no preparation (Exp 3). Ss consisted of 10 medical students aged 23–29 yrs in Exp 1, 12 Ss aged 23–31 yrs in Exp 2, and 11 Ss in Exp 3. Hand–motor preparation was reflected in CNV getting larger fronto–centrally, with this topography being different from the effect in Exp1. Thus, 2 different kinds of motor preparation appear to be reflected by CNV. One kind may consist of assembling and maintaining the stimulus–response links appropriate to the expected S2 patterns, the other is for activating the hand–motor area. These 2 motor contributions to CNV might reflect the 2 aspects of the parieto–frontal motor system.