Figure 1.

To achieve a precision grip movement, the goal of the task is sent to an inverse model (1) that generates a motor command. Due to this motor command, a movement of the upper limb is generated. In parallel, a forward sensory and motor model (2) is generated. This forward model predicts the movement induced by the motor command and estimates the sensory feedback of the new state of the hand and arm. It allows comparison with actual feedback (4) and consequently there is an updating of the motor command. Actual feedback emanates from sensors and is transmitted to the feedback controller (4) after sensory processing (3). The red dotted frame represents the feedforward components, and the green frame denotes the feedback components. Both can be affected at different levels in unilateral brain lesions, with consequential impairment to precision grip.