[Abstract Title]. - Society for Neuroscience

Abstract: Patients with Parkinson‟s Disease (PD) have an impaired ability to respond to
transient postural perturbations and impaired kinesthesia (Horak et al. 1992; Dimitrova et al.
2004). To determine whether patients with PD have impaired steady-state postural responses
similar to patients with sensory deficits, we measured body sway during continuous, saggital
plane, support surface rotations. Eight patients with moderately severe PD (age=64±7.2 yrs) and
8 age-matched controls (age=64±7.5 yrs) performed tests during which the support surface was
rotated using pseudorandom stimuli having peak-to-peak amplitudes of 1°, 2°, or 4°. PD patients
were tested both on (HY= 2.0±0.80) and off (HY=2.8±1.1) medication, and all subjects were
tested with eyes closed. To quantify the relationship between stimulus (support surface rotation)
and response (COM rotation), we used spectral analysis to calculate transfer functions. We
interpreted the results using a simplified feedback model of the postural control system (Peterka
2002). By fitting the model to our experimental transfer functions, we estimated sensory
weighting, postural (active and passive) stiffness and damping, time delay, and force-feedback
parameters. Here, we focus on sensory re-weighting, which reflects active regulation of the
sensory integration process. Consistent with previous results in younger controls, our older
control subjects re-weighted the relative contribution of sensory information for different
stimulus amplitudes (p