Ipsilateral movement-evoked fields reconsidered

The generation mechanism of movement-evoked fields (MEFs) is poorly known and the existence of ipsilateral MEFs is still in dispute. We recorded whole-scalp neuromagnetic activity from eight subjects who were pressing response keys alternately with the right 2nd and 4th digits, while keeping the left palm on the table containing the keys. Clear ipsilateral MEFs peaked 58 +/- 2 ms after the key touch, with sources in the hand area of the right primary somatosensory cortex. The ipsilateral MEFs decreased to half size when the resting left hand was palm up on the table. However, very similar responses were obtained when another person operated the response keys and the subjects just kept their left palm on the table. No signals were elicited when the subjects only viewed these actions with no hand contact to the table. The results indicate that the MEFs receive a strong contribution from tactile input. In our experiment the ipsilateral sensorimotor activation was triggered by the movement-related vibrations transmitted to the resting hand.