Neuronal activity in the monkey ventrolateral thalamus following perturbations of voluntary wrist movements

Extracellular single-cell recordings were made from the cerebellar thalamus (89 neurones) and the VPLc (53 neurones) of three conscious monkeys. The animals were trained to perform wrist movement paradigms including: (a) visually triggered skilled, voluntary movements; (b) 100-ms duration torque pulse perturbations applied during a hold period (termed Pa perturbations); (c) 100-ms perturbations that commenced 100 ms after the visual trigger but during preparation before a skilled, voluntary movement (termed Pb perturbations); and (d) 100-ms perturbations during the skilled, voluntary movement (termed Pm perturbations). These Pb and Pm perturbations were used to identify central and peripheral influences on patterns of neuronal discharge in the ventrolateral thalamus. There was no systematic difference between the responses to Pb and Pm perturbations of neurones in the cerebellar thalamus and those in VPLc. The responses of VPLc and cerebellar thalamic neurones to Pa perturbations were considered to represent transduction of peripheral afferent input, and these responses were compared with the responses to the other types of perturbations. Up to 40% of neurones in cerebellar thalamus and VPLc responded to Pb and Pm perturbations in a similar pattern to that which followed Pa perturbations, and therefore most likely represented faithful transduction of peripheral input. However, the response of over half the neurones in VPLc and cerebellar thalamus to Pb or Pm perturbations differed from Pa perturbations in a manner suggesting that central influences had gated the peripheral input. The short-latency response in cerebellar thalamus which was modified by central influences is appropriately timed to contribute to the "intended" response to perturbations of motor cortical neurones.