Cortical distribution of Bereitschaftspotential and negative slope potential preceding mouth-opening movements in humans.

Cortical potentials associated with the voluntary movement of various body parts are known as movement-related cortical potentials, which allow evaluation of the cortical efferent function and other higher functions controlling voluntary movement. The cortical potentials have three main components: the Bereitschaftspotential (or 'readiness potential'), the negative slope and the motor potential. Here, the cortical potentials preceding mouth-opening movements were recorded to investigate which of these components could be observed. Electroencephalograms (EEGs) were recorded from 11 electrodes placed over the scalp (F3, Fz, F4, T3, C3, Cz, C4, T4, P3, Pz and P4) according to the international 10-20 system. Electromyograms (EMGs) were recorded from the anterior belly of the digastric and the masseter. The 10 healthy participants were requested to make brisk and self-paced mouth-opening movements. All data were digitized with a sampling frequency of 200 Hz and stored for off-line analysis. Movement-related cortical potentials were obtained by averaging the EEG, using the digastric EMG onset as a trigger signal. The Bereitschaftspotential was recorded as a gradually increasing, bilaterally widespread negativity starting 1.7 s (mean) +/-0.23 s (S.D.) before the onset of the opening movement. The amplitude, which was measured at movement onset, was maximum at Cz (3.8 +/- 1.3 microV). The negative slope was observed 500-600 ms before the movement onset, and the motor potential was not clearly identified, because of postmotion artefacts. The cortical maps of the Bereitschaftspotential and negative slope combined together before to the mouth opening showed a symmetrical distribution with a maximum at the vertex region. The study reveals that the Bereitschaftspotential and the negative slope, two components of the movement-related cortical potentials, can be observed preceding mouth-opening movements and are similar to those associated with other voluntary movements. Findings such as distribution, amplitude and onset of the potentials could provide important information for studying the cortical control of mandibular movements.