We investigated the different contribution of the corpus callosum (CC) and cerebellum to motor control, in two macaque monkeys trained to perform a precision grip task with one or both hands. Recordings were made from antidromically identified CC cells, and nearby unidentified neurones (UIDs) in the hand representation of the supplementary motor area (SMA), and compared with cells from the deep cerebellar nuclei (DCN). All cells showed their greatest modulation in activity (rate change locked to particular task event) during the movement epochs of the task (CC 21.3±22.2, UIDs 36.2±30.1 spikes/s for contralateral trials, DCN 63±56.4 for ipsilateral trials, mean±SD). Surprisingly, CC cells fired at very low basal rates compared to UIDs (3.9±4.9 vs 10±9.1 spikes/s) or DCN neurons (50.8±23.8 spikes/s). However, SMA cells had the greatest rate modulation to baseline ratio (CC: 12.1±13.7; UID: 5.3±5.4; DCN: 1.7±2.0). This would allow them to code the timing of a behavioural event with better fidelity than DCN cells. A multivariate regression analysis between cell firing and EMG measured cells’representation of moment-by-moment modulations in muscle activity. CC neurons coded these real-time behavioural parameters significantly less well than the other cells types, using both linear and non-linear models. Basal firing rate substantially constrains cell function. CC cells with low basal rates have restricted dynamic range for coding continuous parameters, but efficiently code the time of discrete behavioural events. DCN neurones with higher basal rates are better suited to control continuously variable parameters of movement.