Walsh & Hoyt: Disorders of Visually Guided Reaching and Grasping

Reaching and grasping external objects is a fundamental activity that demands the coordination of several different nervous system functions. To accomplish this task, the brain transforms a targets visual coordinates to body-centered space, plans a hand path and trajectory (the sequence of hand position and velocity to target), and computes multiple joint torques, especially about the shoulder and elbow. It also specifies the necessary limb segment orientations from among many possibilities, activates appropriate muscle groups, and inhibits others to meet those specifications. The sensory feedback, frames of reference, and neural mechanisms used to solve these complex motor control problems are active research topics.