Impaired Sensory Gating During Standing Balance in Parkinson's Disease

While motor deficits in Parkinson's disease (PD) are well-studied, the role of somatosensory processing in postural instability remains unclear. It is unknown whether sensory gating, a mechanism for filtering irrelevant sensory input, is impaired during standing balance in individuals with PD. To address this, we investigated cortical sensory processing in individuals with PD, age-matched older adults (OA), and young adults (YA) as they performed four balance tasks of increasing difficulty. We measured postural sway using a force platform and recorded somatosensory-evoked potentials (SEPs) from the primary somatosensory cortex (S1) following tibial nerve stimulation. Our results showed a clear dissociation between behavior and neurophysiology. Although postural sway was comparable between the PD and OA groups, only the OA and YA groups showed intact sensory gating, with SEP amplitudes decreasing as the balance challenge increased. In contrast, participants with PD demonstrated consistently elevated SEP amplitudes across all conditions. This study provides the first direct evidence of impaired sensory gating during standing balance in PD. These findings indicate a fundamental deficit in the cortical processing of sensory information essential for postural control. Consequently, they underscore the critical need for therapeutic interventions that target sensory integration deficits, not just motor symptoms.