Alpha-gamma dissociation during slow tracking movements of the monkey's wrist: preliminary evidence from spinal ganglion recording.

Conventional glass-coated Pt-Ir microelectrode technique was adapted for use in recording single unit activity in the cervical dorsal root ganglia of chronic awake behaving monkeys. The activity of one fully identified and four putative afferents from forearm muscle spindles was recorded as a trained monkey performed wrist movements, guided by a visual display, in pursuit tracking of slow predictable hold-ramp-hold target trajectories. Comparison of spindle afferent discharge with parent muscle EMG provided evidence of gamma fusimotor activity dissociated from the activity of homonymous a motoneurons. This appears to maintain a uniform pattern of afferent activity in the face of widely varying parent muscle activity.