Neural control of limb movement


Many chronic unit recording studies have documented how neurons covary with movement parameters, although simple interpretations of neural function in terms of explicit representation are problematic [1].  Moreover, such covariations cannot establish causal relationships.  To identify those cells that have causal effects on muscles we used spike-triggered averages of muscle activity to document post-spike effects of cells on motoneurons (Fig. 1). By knowing both the response patterns of these cells during movements and their output connections to target muscles we can make important causal inferences about their contribution to movements. Premotor cells were documented in motor cortex [2], red nucleus [3], dorsal root afferent fibers [4] and spinal interneurons [5]; all groups showed characteristic response patterns during alternating ramp-and-hold wrist movements [6] (Fig. 2).  Motor cortex cells with correlational linkages to muscles (CM cells) affected multiple target muscles and had specific relations to movements; in contrast, spinal cord interneurons had smaller muscle fields and were active through broader ranges of movement (Fig. 3).




  1. Fetz EE, Are movement parameters recognizably coded in activity of single neurons?, Behavioral and Brain Sciences, 15: 679-690, 1992. [PDF]
  2. Fetz EE, and Cheney PD, Post-spike facilitation of forelimb muscle activity by primate corticomotoneuronal cells, Journal of Neurophysiology 44:751-772, 1980. [PDF]
  3. Cheney PD, Fetz EE, and Mewes K, Neural mechanisms underlying corticospinal and rubrospinal control of limb movements, Progress in Brain Research, 87: 213-252, 1991. [PDF]
  4. Flament D, Fortier PA, and Fetz EE, Response patterns and post-spike effects of peripheral afferents in dorsal root ganglia of behaving monkeys, Journal of Neurophysiology 67: 875-889, 1992. [PDF]
  5. Perlmutter SI, Maier MA, and Fetz EE, Activity and output linkages of spinal premotor interneurons during voluntary wrist movements in the monkey, Journal of Neurophysiology, 80: 2475-2494, 1998. [PDF]
  6. Fetz EE, Perlmutter SI, Prut Y, Seki K, and Votaw S, Roles of primate spinal interneurons in preparation and execution of voluntary hand movement, Brain Research Reviews, 40: 53-65, 2002. [PDF]



Figure 1. Synaptic links mediating post spike facilitation [2]

Figure 2. Response patterns of premotor neurons [6]

Figure 3. Contrast between connections and activity of cortical and spinal premotor neurons