THE SIGNIFICANCE OF SOMATOSENSORY STIMULATIONS TO THE HUMAN FOOT IN THE CONTROL OF POSTURAL REFLEXES

The purpose of this study was to investigate the possible pathways in the somatosensory system that relate to the postural reflexes in the l eg muscles during a sudden, toes-up platform rotation. The inputs to t he cutaneous mechanoreceptors in the sole of the foot as well as to th e joint receptors in the ankle joint were modulated by standing on dif ferent supporting surfaces and by immobilizing the ankle joints; and t hree leg muscle responses (characterized by short latency, medium late ncy, and long latency) to the platform movement were recorded in 15 he althy young subjects. It was found that: (1) the short latency was not affected by the changes in either plantar pressure or ankle joint mov ement; (2) the medium latency was regulated by the plantar pressures u nder the foot, as sensed by the cutaneous mechanoreceptors in the sole of the foot, and by the ankle joint movement, as perceived by the joi nt receptors in the ankle joint; (3) the long latency was also related to the ankle joint movement, but this relation seems to be modulated by the plantar pressures under the foot; and (4) both medium and long latencies were well correlated with the time derivative of the pressur e difference between the forefoot and the rear foot regions (r=0.7), a s well as with the static pressure in the antagonist foot region (r>0. 6).