Monkey vocalization and cortical field potential

Abstract

Cortical field potentials were recorded in monkeys performing self-paced or audio-initiated vocalizations with electrodes implanted on the surface and at a 2.0–3.0 mm depth in the cortex, before and after hemicerebellectomy. A surface-negative, depth-positive (s-N, d-P) slow potential (readiness potential for self-paced vocalizations) was recorded in the supplementary motor, premotor, motor and somatosensory cortices. The right cerebellar hemispherectomy eliminated the readiness potentials in the left premotor (homolog of Broca's area) and motor cortices, and changed the tone. This suggested that the neocortical area, homologous to the human speech area, took part in the generation and control of monkey vocalization with the cerebellum, possibly through cerebro–cerebellar interactions. In audio-initiated vocalizations, a s-N, d-P potential was recorded at 70 ms after stimulus in the rostral bank of the inferior limb of the left arcuate sulcus, as in audio-initiated hand movements. In the motor cortex, a s-N, d-P slow potential was recorded at about 200 ms from the stimulus and 700 ms before vocalization, being almost similar to that in self-paced vocalizations. Reaction times were longer and more variable in audio-initiated vocalizations than audio-initiated hand movements. This suggested that central nervous mechanisms in audio-initiated vocalizations differed from those for audio-initiated hand movements.