The perception of movements elicited by magnetic cortex stimulation depends on the site of stimulation

Previous reports suggest that magnetic cortical stimulation (MCS) of the motor cortex can elicit a sensation of movement (kinaesthesia) in paralysed limbs. To assess this sensory effect of MCS, we examined the accuracy of kinaesthetic perception of stimulus-induced right elbow flexion in six blindfolded, healthy subjects. Matching of movements elicited by MCS was compared with matching of passive elbow movements. Small flexion movements between 1.5 and 5 degrees of angle were regularly overestimated by 50-100% when induced by MCS over the parietal cortex, whereas movements elicited by MCS over the frontal cortex or by passive elbow flexion were accurately estimated. Our results provide data compatible with the hypothesis of the existence of a "central sense of movement". Activation of collateral branches projecting from the motor cortex to the sensory could be the underlying mechanism to this phenomenon.