Cerebellar thalamic activity in the macaque monkey encodes the duration but not the force or velocity of wrist movement

The way in which the cerebellum influences the output of the motor cortex is not known. The aim of this study was to establish whether information about force, velocity or duration of movement is encoded in cerebellar thalamic discharge and could therefore be involved in the modulation of motor cortical activity. Extracellular single cell recordings were made from the cerebellar thalamus (66 neurones) and VPLc (49 neurones) of four conscious macaques performing simple wrist movements with various load and gain conditions imposed. A significant correlation (Spearman's; P < 0.05) was found between movement duration and the duration of neuronal discharge of most cerebellar thalamic neurones (65%), the velocity of movement and rate of neuronal discharge of some cerebellar thalamic neurones (23%), but not between force of movement and rate of neuronal discharge of any cerebellar thalamic neurones. Similar relationships were found between the activity of VPLc neurones and these movement parameters. The strength of the correlations increased when many cells were grouped and analysed as an ensemble, suggesting that populations of cerebellar thalamic (and VPLc) neurones can encode a signal with higher fidelity than single neurones alone. The ensemble data confirmed that the most robust association was between the duration of neuronal discharge and movement duration. We propose that the cerebellum does not provide the motor cortex with specific information about movement force or velocity, but rather that its major role is in activating many motor cortical regions for a specific duration, thus influencing the timing of complex movements involving many muscles and joints.