Disruption of right posterior parietal cortex by continuous Theta Burst Stimulation alters the control of body balance in quiet stance.

Control of body balance relies on the integration of multiple sensory modalities. Lightly touching an earth-fixed reference augments the control of body sway. We aimed to advance the understanding of cortical integration of an afferent signal from light fingertip contact (LT) for the stabilisation of standing body balance. Assuming that right-hemisphere Posterior Parietal Cortex (rPPC) is involved in the integration and processing of touch for postural control, we expected that disrupting rPPC would attenuate any effects of light touch. Eleven healthy right-handed young adults received continuous Theta Burst Stimulation over the left- and right-hemisphere PPC with sham stimulation as an additional control. Before and after stimulation, sway of the blindfolded participants was assessed in Tandem-Romberg stance with and without haptic contact. We analysed sway in terms of the variability of Centre-of-Pressure (CoP) rate of change as well as Detrended Fluctuation Analysis of CoP position. Light touch decreased sway variability in both directions but showed direction-specific changes in its dynamic complexity: a positive increase in complexity in the mediolateral direction coincided with a reduction in the anteroposterior direction. rPPC disruption affected the control of body sway in two ways: first, it led to an overall decrease in sway variability irrespective of the presence of LT; second, it reduced the complexity of sway with LT at the contralateral, non-dominant hand. We speculate that rPPC is involved in the active exploration of the postural stability state, with utilisation of LT for this purpose if available, by normally inhibiting mechanisms of postural stiffness regulation.