The effects of alteration of effector and side of movement on movement-related cortical potentials.

The amplitude of the movement-related cortical potential (MRCP) preceding self-paced voluntary movements is larger if subjects alter between flexions of two fingers compared with repetitive movements of the same finger. However, earlier studies were confined to alternating movements between limbs only and therefore could not differentiate effects of between-limbs from within-limb alteration. The present study was designed to examine effects of alteration of finger (from index to middle, and vice versa) and hand (from left to right, and vice versa) independently from each other. MRCPs were recorded in 20 right-handed healthy young subjects with electrodes placed at Fp1, Fp2, F7, F3, F4, F8, T7, C5, C3, C1, C2, C4, C6, T8, P7, P3, P4, P8, O1 and O2. Subjects made self-paced flexion movements with the index or middle finger of each hand by pressing one out of 4 response buttons. In the alternating conditions, subjects pressed two buttons in a strictly alternating fashion. Every finger was combined with every other finger, arriving at a total of 6 alternating conditions. In the 4 regular conditions, subjects pressed a particular button repetitively across trials. The results show the following: (1) MRCPs over contralateral sensorimotor areas are higher if subjects change the side of movement than if the movements are done with the same hand repeatedly. (2) MRCPs over lateral parietal areas are higher for ipsilateral than contralateral movements in the regular conditions but also increase contralaterally after a change of the side of movement. (3) Any change of side or finger is associated with a widespread increase of negativity over the left hemisphere.