Disentangling cerebellar and parietal contributions to gait and body schema: a repetitive transcranial magnetic stimulation study

The overlap between motor and cognitive symptoms resulting from posterior parietal cortex (PPC) and cerebellar lesions can mask their relative contribution in sensorimotor integration processes. This study aimed to identify distinguishing motor and cognitive features to disentangle PPC and cerebellar involvement in two sensorimotor-related functions: gait and body schema representation. Thirty healthy subjects were enrolled and randomly assigned to PPC or cerebellar stimulation. Sham stimulation and 1Hz repetitive Transcranial Magnetic Stimulation were delivered over P3 or cerebellum before balance, walking and distance estimation tasks. Each trial was repeated with eyes open (EO) and closed (EC). Gait spatiotemporal and kinematic variables were recorded by eight inertial measurement units. Instability increased in both groups after real stimulation vs. sham stimulation: PPC inhibition increased the instability in EC conditions, while cerebellar inhibition affected both EC and EO stability. Spatiotemporal variability increased after real stimulation (EC vs EO) in both groups but mostly affecting different parameters. Increased kinematic variability of ankle and knee angles was observed in both groups after real stimulation (EC vs. EO). Distance overestimation was observed after real stimulation (EC) only in the PPC group. Stability, gait variability and distance estimation parameters can be used to disentangle cerebellar and PPC sensorimotor integration deficits. Differential diagnosis efficiency can benefit from this methodological approach.