Behavioral and Motor Mechanisms of Dorsomedial Frontal Cortex of Macaca Monkey

Abstract

The activity of 249 neurons in the dorsomedial frontal cortex was recorded in two macaca monkeys. The animals had been trained for saccades and fixation tasks in an unrestrained condition. We found 51 burst neurons that showed a double-firing discharge. We observed two different patterns of discharge. In one case the first burst occurred before the arm movement, the second before the related eye movement. In the second case, the first discharge took place before a neck contraction followed by a second burst before eye movement. Some cells showed two discharges, one that preceded the bar-press and the other the saccade. With other cells the discharges preceded the bar-release and then saccade. Still other cells discharged three times: first before the bar-press, second before release and third before the orienting saccade. Some cells were active for the bar-press and for the first orienting saccades. These cells were active also for a large range of movement tested at the presentation of natural stimuli. Electrical stimulation failed to evoke either arm or eye movements. Neck-eye cells are related to movement of the eye and to an increase of EMG activity independent of eye position. The electrical stimulation evoked eye movements and EMG increases at low threshold.

The activity of arm-eye cells related to purposeful movement with the ineffectiveness of electrical stimulation may be ascribed to a motor reactivation or an ordering signal. The neck-eye cells may be considered trigger commands for neck-eye coordination.

These results suggest that dorsomedial frontal cortex is an area where the behavioral processes and motor plannings are matched, probably for the selection of eye-head-arm motor strategies.

Key Words:

• dorsomedial frontal cortex
• arm-eye neurons
• neck-eye neurons.