How are postural responses to external perturbations affected by PD

Abstract People with Parkinson disease (PD) have particular difficulty recovering equilibrium in response to backward perturbations compared to other directions. The postural responses to external perturbations are weak and slow in PD (bradykinetic) compared to healthy older subjects but have normal onset latency. Muscle cocontraction and stiff joints impair postural responses to perturbations in people with PD. The inability to quickly change the pattern of postural response to changes in environmental context is unique to PD. Levodopa does not improve the strength or adaptation of postural responses. Deep brain stimulation (DBS) in subthalamic nucleus (STN) further impairs postural responses while DBS in internal Globus Pallidus (GPi) does not improve postural responses. Rehabilitation that includes responding to postural perturbations can improve postural responses in people with PD.