Modulation of fronto-parietal connections during the rubber hand illusion

Accumulating evidence suggests that parieto-frontal connections play a role in adjusting body ownership during the Rubber Hand Illusion (RHI). Using a motor version of the rubber hand illusion paradigm, we applied single-site and dual-site transcranial magnetic stimulation (TMS) to investigate cortico-spinal and parietal-frontal connectivity during perceived rubber hand ownership. Healthy volunteers received a conditioning TMS pulse over left anterior intraparietal sulcus (aIPS) and a test TMS pulse over left primary motor cortex (M1). Motor Evoked Potentials (MEPs) were recorded at rest and during three RHI conditions: (i) agency and ownership, (ii) agency but no ownership and (iii) neither agency nor ownership. Parietal-motor communication differed among experimental conditions. The induction of action ownership was associated with an inhibitory parietal-to-motor connectivity, which was comparable to the aIPS-to-M1 inhibition present at rest. This aIPS-to-M1 inhibition disappeared during movement conditions not inducing ownership. Cortico-spinal excitability was not significantly modulated during the motor RHI as indicated by the task-constant MEP amplitude elicited by the M1 test pulse alone. Our results indicate that the perceived ownership over the rubber hand is associated with normal parietal-motor communication. This communication is disturbed if the sensorimotor conflict between one's own hand and the rubber hand is not resolved.