Set and gain control of posture in cerebellar and vestibular patients

By examining responses to five predictable amplitudes of surface displacement (backward direction, constant velocity), the ability to scale postural responses using central predictive mechanisms was tested. By examining responses to four different displacement velocities (backward direction, constant amplitude), the ability to scale postural responses using peripheral sensory feedback was tested. Response magnitude was quantified as the initial (first 75 ms) rate of change of surface torque response and plotted as a function of displacement amplitude or velocity to determine whether cerebellar or vestibular loss altered postural response gains. Responses of six patients with bilateral vestibular loss were compared with nine cerebellar patients with anterior lobe signs, and with 10 healthy control subjects with similar mean ages and weights. Results indicate that the vestibular and cerebellar patients had two to three times larger postural responses for all displacement amplitudes and velocities than normal subjects. Despite this increase in response bias, the vestibular patients had normal torque response/stimulus velocity or amplitude relationships. In contrast, cerebellar patients showed normal scaling to stimulus velocity but were unable to scale to predicted stimulus amplitudes.<>