Cortical field potentials associated with audio-initiated hand movements in the monkey

Monkeys were trained to respond to auditory stimulus by lifting a lever (audio-initiated hand movement), and field potentials were recorded from various cortical areas with electrodes implanted on the surface and at a depth of 2.0-3.0 mm, depending on the area. Tones of 500, 1000 and 2000 Hz were given to the monkey for about 500 or 10 ms, as auditory stimuli. In association with the movement, potentials of different configurations were recorded respectively in the primary auditory, auditory association, prefrontal, premotor, motor and somatosensory cortices. Initial surface-positive (s-P), depth-negative (d-N) potentials appeared in the primary auditory and auditory association cortices about 20 ms after the onset of the auditory stimulus, and they were often followed by s-N, d-P potentials. In the forelimb area of the motor cortex contralateral to the moving hand, s-N, d-P potentials appeared at a latency of about 100 ms. Following cerebellar hemispherectomy ipsilateral to the moving hand, the s-N, d-P potentials in the forelimb motor cortex were eliminated and reaction times prolonged. The same monkeys were also trained to perform a visuo-initiated movement, and results were compared with each other. Primary sensory and sensory association areas activated during such movements were certainly different, and the prefrontal association cortex appeared to participate much less predominantly in the audio- than in the visuo-initiated movement. Reaction times were generally longer and more variable for the audio- than for the visuo-initiated movement. Nevertheless the cerebello-thalamo-motor cortical projection was found to be recruited in the same manner prior to both movements.