Neurons in human motor thalamus encode reach kinematics and positional errors related to braking

Deep brain stimulation of the cerebellar-receiving region of motor thalamus, the ventral intermediate nucleus of the thalamus (VIM), effectively reduces the action tremor associated with essential tremor. However, the neural contribution of the VIM to the control of voluntary movement, and how that function relates to action tremor pathophysiology, is not well understood. In single thalamic neurons recorded during a naturalistic reaching task in essential tremor patients undergoing deep brain stimulation surgery, we find that firing rate changes align with the braking and stabilizing phases of reach movements, encode hand position and velocity above other kinematic variables, and strongly encode error signals relating the current hand position to the final reach target position. These findings support a hypothesis that the VIM contributes to the control of accurate stopping and stabilization of the hand, dysfunction of which aligns with models of action tremor generation.