Relationship between the velocity of illusory hand movement and strength of MEG signals in human primary motor cortex and left angular gyrus.

We studied the relationship between the velocity of movement illusion and the activity level of primary motor area (M1) and of the left angular gyrus (AG) in humans. To induce illusory movement perception, we applied co-vibration at different frequencies on tendons of antagonistic muscle groups. Since it is well established that the velocity of illusory movement is related to the difference in vibration frequency applied to two antagonistic muscles, we compared magnetoencephalography (MEG) signals recorded in two conditions of co-vibration: in the "fast illusion" condition a frequency difference of 80 Hz was applied on the tendons of the right wrist extensor and flexor muscle groups, whereas in the "slow illusion" condition a frequency difference of 40 Hz was applied on the same muscle groups. The dipole strength, reflecting the activity level of structures, was measured over M1 and the left AG in two different time-periods: 0-400 and 400-800 ms in each condition. Our results showed that the activity level of the AG was similar in both conditions whatever the time-period, whereas the activity level of M1 was higher in the "fast illusion" condition compared to the "slow illusion" condition from 400 ms after the vibration onset only. The data suggest that the two structures differently contributed to the perception of illusory movements. Our hypothesis is that M1 would be involved in the coding of cinematic parameters of the illusory movement but not the AG.