The relationship between monkey ventrolateral thalamic nucleus activity and kinematic parameters of wrist movement

Extracellular recordings were made from single neurones in the cerebellar thalamus (75 neurones) and the VPLc (44 neurones) of four conscious moving monkeys. The experiment was designed to establish whether the discharge of ventrolateral thalamic neurones encodes information about kinematic parameters. The animals were trained to resist unexpected perturbations of the wrist and to perform skilled, voluntary wrist movements, producing stereotyped reflex and active movements with a wide range of durations and amplitudes. Statistical analysis of the discharge pattern associated with individual trials of movement was performed. In various maintained wrist positions there was a significant correlation (P < 0.05) between frequency of tonic discharge and joint position in 40% of the cerebellar thalamic neurones and in 54% of VPLc neurones. The phasic neuronal discharge associated with stereotyped movement often appeared 'velocity- or acceleration-like'. However, statistical analyses revealed that the phasic discharge of only a small percentage of cerebellar thalamic and VPLc neurones was correlated with duration of movement, peak velocity or acceleration. The percentage of cerebellar thalamic neurones with discharge correlated to kinematic parameters was much greater when an unexpected change in the gain between joint angle and screen display led to errors in tracking the target. It is concluded that the cerebello-thalamo-cortical (CTC) pathway carries information regarding maintained joint position but not velocity or acceleration of movement during a stereotyped task. However, the CTC pathway has a greater capacity to signal information about movement velocity and acceleration when there is a mismatch between the intended and actual movement.