Relationship between Weight Perception Illusion and Excitability of the Primary Motor Cortex

We investigated the phenomenon of the weight illusion being induced by creating a temporal difference between an object's motion information (lifting) and its visual information (lifted) in the grasping exercise. We investigated the activity of the primary motor cortex (M1) by examining the excited state of this area during presentation of a visual transmission delay. Using motor evoked potentials (MEP), which enables the evaluation of the activation state of M1 based on the amplitude magnitude, illusion-dependent changes in MEP were observed. We used here a virtual reality device with a stereoscopic object gripping system using two haptic devices. Our findings indicate that weight perception illusions did not influence primary motor cortex excitability. Furthermore, it was found that the rate of increase in MEP immediately after grasping and raising the object was significantly larger than after it was sufficiently held and raised. These results indicate differentiated motor cortex activities specific for each stage of movement.