Cortical control of postural responses

Abstract

This article reviews the evidence for cortical involvement in shaping postural responses evoked by external postural perturbations. Although responses to postural perturbations occur more quickly than the fastest voluntary movements, they have longer latencies than spinal stretch reflexes, suggesting greater potential for modification by the cortex. Postural responses include short, medium and long latency components of muscle activation with increasing involvement of the cerebral cortex as latencies increase. Evidence suggests that the cortex is also involved in changing postural responses with alterations in cognitive state, initial sensory-motor conditions, prior experience, and prior warning of a perturbation, all representing changes in "central set." Studies suggest that the cerebellar-cortical loop is responsible for adapting postural responses based on prior experience and the basal ganglia-cortical loop is responsible for pre-selecting and optimizing postural responses based on current context. Thus, the cerebral cortex likely influences longer latency postural responses both directly via corticospinal loops and shorter latency postural responses indirectly via communication with the brainstem centers that harbor the synergies for postural responses, thereby providing both speed and flexibility for pre-selecting and modifying environmentally appropriate responses to a loss of balance.

Fig. 1

A simple model of proposed neural pathways involved in cortical control of short, medium and long latency automatic postural responses to external perturbations

Fig. 2

Effects of prior knowledge of onset time of an upcoming surface perturbation on electroencephalographic readiness potentials and center of pressure responses from a representative healthy adult. A An EEG readiness potential shows slow negativity starting 500 ms after a visual cue and 1500 ms before a surface perturbation, seen only in the trials with a visual warning cue that turned on 2000 ms before the perturbation. B Center of pressure displacements show a larger distance between the maximum forward displacement of the center of pressure and the front edge of the foot (the stability margin) in trials with a cue compared to trials without a cue