Body representation in the posterior parietal cortex: an investigation of gait and postural control parameters associated with parietal functional inhibition

Research shows multisensory integration in the posterior parietal cortex (PPC) as well as body representations, though most research is limited to reach-to-grasp experiments with representations of the hand, rather than whole body representation using the body schema. This paper aims to look at the role of the PPC from a neurophysiological perspective (by analyzing postural control and gait alterations) and from a neuropsychological perspective (by investigating alterations in the body schema). Using a virtual lesion approach with low frequency (1Hz) rTMS, participants underwent an inhibitory stimulation to their PPC. Subjects performed three main motor tasks that evaluated their postural control, gait and distance estimation abilities. Postural control parameters and spatiotemporal parameters were measured using Inertial measurement units (IMUs). The three tasks were performed with the eyes open and closed, to allow examine the difference between visually supported conditions and proprioceptive reliant conditions. It was hypothesized that increased instability in postural control would be found in real stimulation conditions with eyes closed. Secondly, it was expected to see higher variation in spatiotemporal parameters in gait. Lastly, it was hypothesized to see a lower capability for distance estimation due to alterations in the body schema. Results show a general increase in instability during the real stimulation condition with eyes closed (compared to sham). Additionally, during the walking tasks a higher variability in two spatiotemporal parameters was observed after the real stimulation (with eyes closed) compared to the sham with eyes closed; while the difference between open eyes and closed eyes after the real stimulation increases in five spatiotemporal parameters. Lastly, participants showed an overestimation of distance only in the long-distance conditions with eyes closed during the real stimulation. In conclusion, the statistically significant results found are in line with previous literature and indicate alterations of the body scheme likely due to dysfunctional sensorimotor integration. Limitations of the experiment, such as small sample size are discussed, thus further replications would be beneficial for generalizability. The experiment shows promising results for future research and for clinical application.