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Neurons Of The Anterior Mesial Cortex Related To Faciovocal Activity In The Awake Monkey

R. A. West, C. R. Larson

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1. The anterior mesial cortex, including the cingulate region, is thought to be involved in the voluntary control of vocalization. Previous recording studies have demonstrated that anterior mesial neurons discharge before conditioned and spontaneous vocalizations, but questions remain regarding the location and functional properties of these neurons. The present study was performed to provide a more complete description of the location and discharge properties of anterior mesial neurons involved in faciovocal behaviors. 2. Single-unit activity was recorded from neurons in the anterior mesial cortex of monkeys during performance of self-paced vocalizations and jaw openings. Cells were also tested for responsiveness to acoustic stimulation, and attempts were made to elicit vocalization through stimulation of the cortex surrounding related cells. Discharge properties of the cells were statistically analyzed, and correlation analysis was performed between measure of cell discharge and vocalization. 3. A total of 145 neurons were observed to modulate their discharge in association with vocalization or jaw opening. Four general classes of neurons were observed: neurons related only to vocalization, neurons related only to jaw opening, neurons related to both vocalization and jaw opening, and neurons related to other oromotor activities such as lip movements or reinforcement consumption. 4. Vocalization-related cells typically discharged tonically at a low frequency (mean 22 Hz), and many instances of long-lead activity (lead time > 500 ms) were noted. No neurons responded to acoustic stimulation, and electrical stimulation failed to elicit vocalization. Neural activity was not correlated with any measure of vocalization. 5. Neurons related to faciovocal behavior were located in the anterior cingulate sulcus and adjacent cortex of the mesial wall at a level just rostral to the genu of the arcuate sulcus. This region roughly corresponds to the rostral cingulate motor area and is located caudal to the traditionally described cingulate vocalization region. 6. In the present study we demonstrate the existence of an additional region in the medial wall that is involved in a variety of faciovocal behaviors such as vocalization, jaw opening, lip movements, and reinforcement consumption. The neurons do not appear to be strongly coupled to the execution of these acts. These results suggest that the activity of neurons in the anterior mesial cortex may relate to faciovocal behavior in a more global way than the activity of neurons in other motor areas.