A no-stimulus, no-response, event-related potential of the human cortex

Abstract

Brain macropotentials related to self-paced uni- or bimanual, unskilled or skilled movements were recorded from the motosensory cortical areas from 26 subjects. EMG of the active muscles, respiration, GSR, ECG and potentials generated by eye movements were also recorded. Subjects triggered the sweep of an oscilloscope with self-paced thumb movements in the following, unskilled, conditions: left-hand press (LHP), right-hand press (RHP), pressing with both hands simultaneously. They then performed a skilled performance task (SPT) during which the sweep was initiated by an LHP and was terminated within 40–60 msec by an RHP. Ten of the tested subjects participated in a variation of the skilled performance task during which no visual feedback was provided about their performance. All movements were preceded by sustained negativities known as N 1 component or Bereitschaftspotential (BP). All actions were followed by the motor cortex potential (MCP) with a latency of 32 msec from the EMG peak and a positivity with a latency of 200 msec from movement execution and initiation of the oscilloscope trace. Only the movements during SPT were followed by an additional positivity with a latency of 460 msec from the movement, having a centroparietal distribution and a mean amplitude at the vertex of 12.7 μV and S.D. of 5.0 μV. This skilled performance positivity (SPP) was independent of the amplitude of the previous BP and MCP and it was absent when the subject executed a variation of the SPT test during which visual feedback was not provided. Thus the SPP potential seems to be independent of stimulus or response characteristics and develops under experimental circumstances in which the subject expects and receives information about the outcome of coordinated self-placed movements.