THE RELATIONSHIP BETWEEN MONKEY VENTROLATERAL THALAMIC NUCLEUS ACTIVITY AND KINEMATIC PARAMETERS OF WRIST MOVEMENT

Extracellular recordings were made from single neurones in the cerebel lar thalamus (75 neurones) and the VPLc (44 neurones) of four consciou s moving monkeys. The experiment was designed to establish whether the discharge of ventrolateral thalamic neurones encodes information abou t kinematic parameters. The animals were trained to resist unexpected perturbations of the wrist and to perform skilled, voluntary wrist mov ements, producing stereotyped reflex and active movements with a wide range of durations and amplitudes. Statistical analysis of the dischar ge pattern associated with individual trials of movement was performed . In various maintained wrist positions there was a significant correl ation (P < 0.05) between frequency of tonic discharge and joint positi on in 40% of the cerebellar thalamic neurones and in 54% of VPLc neuro nes. The phasic neuronal discharge associated with stereotyped movemen t often appeared 'velocity- or acceleration-like'. However, statistica l analyses revealed that the phasic discharge of only a small percenta ge of cerebellar thalamic and VPLc neurones was correlated with durati on of movement, peak velocity or acceleration. The percentage of cereb ellar thalamic neurones with discharge correlated to kinematic paramet ers was much greater when an unexpected change in the gain between joi nt angle and screen display led to errors in tracking the target. It i s concluded that the cerebello-thalamo-cortical (CTC) pathway carries information regarding maintained joint position but not velocity or ac celeration of movement during a stereotyped task. However, the CTC pat hway has a greater capacity to signal information about movement veloc ity and acceleration when there is a mismatch between the intended and actual movement.