PARCELLATION OF HUMAN MESIAL AREA-6 - CYTOARCHITECTONIC EVIDENCE FOR 3 SEPARATE AREAS

The mesial sector of primate area 6 is usually described as consisting of two distinct areas: the supplementary motor area (SMA or SMA prope r) and the pre-SMA. Recent human brain imaging studies showed, however , that this subdivision is not completely satisfactory and that, most likely, SMA proper consists of two functionally distinct parts. In ord er to elucidate whether this hypothesis has an anatomical counterpart, we examined the cytoarchitectonic organization of human mesial area 6 in three brains of subjects deceased without any previous sign of neu rological disorders. The data showed that human mesial area 6 consists of three separate cytoarchitectonic areas. Two of them are located mo stly caudal to the vertical line transversing the anterior commissure (VCA line), the third one is located rostral to it. Given the location and some architectonic similarities between the two caudal areas, we named them caudal SMA (SMAc) and rostral SMA (SMAr). The area rostral to the VCA line is referred to as pre-SMA. The possible functional rol e of the three areas is discussed.