Primate spinal interneurons: muscle fields and response properties during voluntary movement.

Publisher Summary The current view of the functions of spinal interneurons in generating voluntary movements is based on inferences from observations in anesthetized, immobilized animals. Previous studies have elucidated the convergent inputs to interneurons from afferent fibers and descending tracts. Yet, little is known about two crucial properties that are essential to understanding the functions of segmental neurons in movements: their activity patterns during normal voluntary limb movements and their output effects on the agonist muscles. These two properties together provide significant information about how the activity of spinal neurons contributes to muscle activity. Similar studies have elucidated the response patterns and the output effects of supraspinal premotor (PreM) neurons in the motor cortex and red nucleus and dorsal root afferent fibers. This chapter summarizes the results of comparable experiments with interneurons in the cervical spinal cord and describes the properties of primate segmental inter-neurons during a similar step-tracking task. Information on the discharge pattern and postspike effects of inter-neurons enables contrasting the relative contributions of supraspinal and segmental PreM neurons to voluntary muscle activity.