Distinct Neuronal Organizations of the Caudal Cingulate Motor Area and Supplementary Motor 1 Area in Monkeys for Ipsilateral and Contralateral Hand Movements 2 3

24 The caudal cingulate motor area (CMAc) and the supplementary motor area (SMA) play important 25 roles in movement execution. The present study aimed to characterize the functional organization of 26 these regions during movement by investigating laterality representations in the CMAc and SMA of 27 monkeys via an examination of neuronal activity during a button press movement with either the right 28 or left hand. Three types of movement-related neuronal activity were observed: (1) with only the 29 contralateral hand, (2) with only the ipsilateral hand, and (3) with either hand. Neurons in the CMAc 30 represented contralateral and ipsilateral hand movements to the same degree, whereas neuronal 31 representations in the SMA were biased toward contralateral hand movement. Furthermore, recording 32 neuronal activities using a linear-array multicontact electrode with 24 contacts spaced 150 μm apart 33 allowed us to analyze the spatial distribution of neurons exhibiting particular hand preferences at the 34 submillimeter scale. The CMAc and SMA displayed distinct microarchitectural organizations. The 35 contralateral, ipsilateral, and bilateral CMAc neurons were distributed homogeneously, whereas SMA 36 neurons exhibiting identical hand preferences tended to cluster. These findings indicate that the 37 CMAc, which is functionally organized in a less structured manner than the SMA is, controls 38 contralateral and ipsilateral hand movements in a counterbalanced fashion, whereas the SMA, which 39 is more structured, preferentially controls contralateral hand movements. 40