Some pathophysiological aspects of the parkinsonian rigidity.

The neurophysiological mechanisms explaining parkinsonian rigidity are still poorly understood. Its reflex nature is well established but the peripheral afferents causing it are likely multiple and not restricted to IA afferents. Few modifications appear in spinal cord reflex mechanisms and are limited to some interneurones (reciprocal inhibition and flexor reflex). At present, the most plausible explanation of rigidity relies on hyperactivity in long loop reflex pathways relaying in the brain.