Spatial distribution of cingulate cells projecting to the primary, supplementary, and pre-supplementary motor areas: a retrograde multiple labeling study in the macaque monkey

We examined the location and spatial distribution of cingulate cortical cells projecting to the forelimb areas of the primary motor cortex (MI), supplementary motor area (SMA), and pre-supplementary motor area (pre-SMA) using a multiple retrograde labeling technique in the monkeys (Macaca fuscata). The forelimb areas of the MI, SMA and pre-SMA were physiologically identified, based on the findings of intracortical microstimulation (ICMS) and single cell recording. Three different tracers, diamidino yellow (DY), fast blue (FB), and wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), were injected into each of the three motor areas in the same monkey. Retrogradely labeled cells in the cingulate cortex were plotted with an automated plotting system. Cells projecting to the forelimb area of the MI were distributed in the two separate regions situated rostrocaudally in the dorsal and ventral banks of the cingulate sulcus, namely the rostral cingulate motor area (CMAr) and caudal cingulate motor area (CMAc). These two regions corresponded to the forelimb areas identified by the ICMS in the same animal. The distribution of projection cells to the SMA overlapped extensively with that of projection cells to the MI. Although the MI received relatively sparse inputs from the CMAr than from the CMAc, the SMA received inputs from the CMAr and its adjacent areas as much as from the CMAc. The projection cells to the pre-SMA were distributed in the anterior portion of the cingulate cortex, including the anterior part of the CMAr and in a small part of the cingulate gyrus. These findings indicate that the MI and SMA share a considerable common information from the cingulate cortex, including the CMAr and CMAc, whereas the pre-SMA receives a different set of information from the anterior part of the cingulate cortex.