Spinal and supraspinal stretch responses of postural muscles in early Parkinsonian patients

► We investigated side-related changes in response to balance perturbation in early PD. ► Toe-down rotation of a platform evokes a medium-latency response (MLR) in the tibialis. ► The spinal (MLR1) and supraspinal (MLR2) components are abnormal in the affected side. ► Poor MLR1 reduction by holding indicates unilateral impairment of descending control. ► Increased MLR2 is related to abnormal basal-ganglia ascending influence to the cortex.