Somatotopy in the ipsilateral primary motor cortex

Conflicting reports exist about the occurrence, reliability and localization of activation in the ipsilateral primary motor cortex (MI). We re-examined this issue with functional magnetic resonance imaging in 12 volunteers performing right hand, finger, wrist, elbow, foot and tongue movements in two separate sessions. Ipsilateral MI activation was inconsistently and non-reliably present during all movements: in 54% of all hand, 50% elbow, 46% finger, 33% wrist, and in 17% of all foot experiments. When compared to contralateral MI, the volumes and maximum t-values were always smaller. The ipsilateral MI body representation was somatotopically organized with coordinates similar to the contralateral MI. Finally, the presence of ipsilateral MI activation depended on the global activation level in other motor-related areas, which was significantly increased, when ipsilateral MI activation was detected.