The role of the medial wall and its anatomical variations for bimanual antiphase and in-phase movements

The medial wall of the frontal cortex is thought to play an important role for bimanual coordination. However, there is uncertainty regarding the exac t neuroanatomical regions involved. We compared the activation patterns rel ated to bimanual movements using functional magnetic resonance imaging in 1 2 healthy right-handed subjects, paying special attention to the anatomical variability of the frontal medial wall. The subjects performed unimanual r ight and left and bimanual antiphase and in-phase flexion and extension mov ements of the index finger. Activation of the right supplementary motor are a (SMA) proper, right and left caudal cingulate motor area (CMA), and right and left premotor cortices was significantly stronger during bimanual anti phase than bimanual in-phase movements, indicating an important function of these areas with bimanual coordination. A frequent anatomical variation is the presence of the paracingulate sulcus (PCS), which might be an anatomic al landmark to determine the location of activated areas. Seven subjects ha d a bilateral, three a unilateral right, and two a unilateral left PCS. Bec ause the area around the PCS is functionally closer coupled to the CMA than to the SMA, activation found in the area around the PCS should be attribut ed to the CMA. With anatomical variations such as the presence of a PCS or a vertical branch of the cingulate sulcus, normalization and determination of the activation with the help of stereotaxic coordinates can cause an inc orrect shift of CMA activation to the SMA. This might explain some of the d iscrepancies found in previous studies.