Postural support of goal-directed movements: the preparation and guidance of voluntary action in man.

Abstract

Goal-directed movements, such as punching and pointing, need preprogramming of postural support and visual control. These processes are recorded in man by EEG, EMG, oculogram, and a platform. The earliest cerebral correlate of voluntary action is the Bereitschaftspotential (readiness potential) or, after a trigger signal, the expectancy wave (CNV). These bilateral negative potential shifts increase to a Zielbewegungspotential (aiming potential) when a goal-directed movement is made, and end with a positive shift, when the goal is reached. During these cerebral potentials an attentive eye saccade is directed towards the target and an ordered sequence of bilateral muscle activations follows. This coordinated motor activity in trunk and leg muscles corresponds to a readiness innervation that prepares body posture and balance. It precedes the final aimed movement of the arm towards the target and postural adjustments such as the compensation of body and head rotation by the vestibular-ocular reflex. The temporal order of the cerebral, oculomotor and muscular events is schematized for punching and pointing movements in a figure. The limits of conscious control and the necessity of automatized learning for voluntary skilled movement under visual control are discussed. Some speculations are made about a possible origin of slow potential shifts by surface negative dipoles in columnar modules of the parasagittal cortex during the programming and monitoring of aimed motion.