Corpus callosum connections of subdivisions of motor and premotor cortex, and frontal eye field in a prosimian primate, Otolemur garnetti

The callosal connections of motor and premotor fields in the frontal cortex of galagos were examined by placing multiple tracers into the primary motor area (M1), dorsal premotor area (PMD), ventral premotor area (PMV), supplementary motor area (SMA), and frontal eye field (FEF) following intracortical microstimulation. Retrogradely labeled neurons in the opposite hemisphere were plotted and superimposed onto brain sections stained with myelin and cytochrome oxidase for architectonic analysis. The main callosal connections of M1 and the caudal portion of PMD (PMDc) were with homotopic sites, and the major callosal connections of the rostral portion of PMD (PMDr), SMA, and FEF were with homotopic sites and adjoining cortex in the frontal lobe. In addition, M1 forelimb representation had sparse callosal connections, whereas M1 trunk and face representations, as well as the premotor areas, had dense callosal connections. The sparse interhemispheric connections of the forelimb sector of M1 suggests that the control of each forelimb is largely from the contralateral M1 in galagos, as in other primates.