Evidence for Somatosensory Components in Movement-Evoked Brain Potentials

Abstract

Electric potentials can be recorded non-invasively from the human scalp with surface electrodes. With digital signal processing the ongoing electroencephalogram is converted into the evoked potentials. These waveforms represent the electric brain potentials in defined time epochs around a stimulus. Thus, the electric brain potentials corresponding to the perception of a stimulus or related to a reaction of the subject can be evaluated. The issue of this paper is the reafferent information elicited by a simple limb movement. Do evoked potentials give evidence for sensory feedback about limb movements? The potential associated with the preparatory phase before the start of a movement (Bereitschaftspotential) has been the subject of numerous investigations (Kornhuber and Deecke, 1965; Bötzel et al., 1993). The Bereitschaftspotential is followed by the “motor potential”, a negative peak at the onset of the movement with the maximum over the hand motor cortex of the hemisphere contralateral to the movement (Kornhuber and Deecke, 1965). At frontal electrodes a potential was described with a peak at 90 ms after the begin of the movement and named “N+50” by Shibasaki (1980) and “frontal peak of the motor potential” by Tarkka and Hallet (1991). These potentials are suspected to signify reafferent somatosensory information. A recent source analysis of the Bereitschaftspotential (Bötzel et al., 1993) revealed a potential at 90 ms after movement onset which was tentatively called reafferent potential. In this paper we report experiments which were designed to elucidate the nature of this potential, its origin, and its behaviour after lesions of the somatosensory pathways.