Lateralised cortical activity due to preparation of saccades and finger movements: a comparative study

The topography and time course of event-related asymmetries of the EEG associated with horizontal saccadic eye movements and finger movements was compared in a 4-choice response task, where the subjects had to respond to the imperative stimulus (S2) by moving the right or left index finger or by making a saccade to the right or the left. The cue stimulus (S1) contained full, partial, or no information about the direction and the effector. In case of finger movements 3 distinct lateralisations were found: (1) increased negativity over the motor cortex contralateral to the future movement direction, (2) increased contralateral negativity at temporoparietal sites beginning 200 ms after delivery of the directional information, and (3) increased ipsilateral negativity at temporo-parietal sites beginning 350-500 ms after delivered direction and effector information. The early temporo-parietal lateralisation was also visible in case of saccadic eye movements and in case of effector-unspecific directional information. Before saccadic eye movements no other distinct lateralisation could be observed at any recording site. In sum, lateralised cortical activities due to preparation processes for finger movements and due to effector-unspecific processing of directional information for motor preparation by the posterior parietal cortex could be demonstrated, whereas no distinct lateralisation due to preparation for saccadic eye movements was visible.