Negative cortical DC shifts preceding and accompanying simple and complex sequential movements

Abstract

Negative cortical DC shifts preceding and accompanying the execution of four different motor tasks were analysed in 18 subjects (Ss): Repetitive flexions and extensions of the forefinger had to be performed either by the right (1) or the left (2) hand. This simple motor task was compared to a complex one in which flexions and extensions of forefinger and hand had to be alternated in a fixed sequence. The complex task had either to be performed by the right (3) or the left (4) hand. Thus, the four conditions differed in the side of the performing hand (right/left) and in task-complexity (simple/complex). After its voluntary initiation, each task had to be performed for at least a period of six seconds. A Bereitschaftspotential (BP) preceded the voluntary initiation of the movement. Task-performance was accompanied by a negative DC shift called a performance-related negativity (N-P). Amplitudes of BP and N-P were compared by analysis of variance (ANOVA) using the factors “performing hand” (right/left) and “task-complexity” (simple/complex). “Performing hand” had significant effects on N-BP and N-P in C3^* and C4^* (positioned over the primary motor cortex) but did not influence mid-central (Cz^*), frontal (F3, Fz, and F4) or parietal (P3, Pz, P4) recordings. “Task-complexity” had significant effects on N-P in mid-central (Cz^*, C1^*, C2^*) and parietal (P3, Pz) recordings with higher negativity for complex movements. Recordings in C3^* and C4^* did not vary with “task complexity”. Dissociative effects of “performing hand” and “task-complexity” indicate that movement-related DC-potential shifts in C3^*/ C4^* can functionally be separated from those recorded in Cz^*. Variations depending on the specific properties of the tasks were found to be larger during performance than during preparation of the task.