Studies on central nervous mechanisms of vocalization in monkeys

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Field potentials were recorded with electrodes chronically implanted on the surface and at 2.0-3.0mm depth in various cortical areas in monkeys trained for vocalizing at self-pace (self-paced vocalization). In three monkeys, surface-negative, depth-positive (s-N,d-P) slow potentials prior to vocalization were led from the premotor, motor and somatosensory cortices and supplementary motor area in both hemispheres. Such premovement potentials were recorded also in the cingulate and prefrontal cortices when a monkey vocalized with strong motivation for reward. Cerebellar hemispherectomy on the right side eliminated the s-N,d-P premovement potentials in the motor cortex and in the posterior bank of the inferior limb of the arcuate sulcus (Broca's homologue) in the left hemisphere. After the operation, the tone came to have less components of different frequencies, and its duration varied much more than before. These facts suggest that the neocortical area homologous to the human speech are … More a takes part in the generation and control of monkey vocalization together with the cerebellum possibly through cerebro-cerebellar interactions. This is against ideas so far proposed on nonhuman primate vocalization, i.e., it is generally considered that animal vocalization differs fundamentally from human speech.Monkeys were also enough trained to vocalize in response to auditory stimulus of a monkey's coo vocalization for more than three months (audio-initiated vocalization). Field potentials on the audio-initiated vocalization were recorded with the electrodes described above, and reaction times were measured from the onset of stimulus to the start of vocalization. A s-N,d-P potential was recorded at a latency of about 70 ms after the stimulus in the anterior bank of the inferior limb of the arcuate sulcus in the left hemisphere in which no significant potential was recorded on self-paced vocalization. In the motor and somatosensory cortices, s-N,d-P potentials were recorded at a latency of about 300 ms. Reaction times were obviously longer and more variable when compared with the audio-initiated hand movements^1 reported before.1.Gemba & Sasaki, Exp.Brain Res. (1987) 65 : 649-657 Less