CONVERGENCE OF LIMBIC INPUT TO THE CINGULATE MOTOR CORTEX IN THE RHESUS-MONKEY

Limbic system influences on motor behavior seem widespread, and could range from the initiation of action to the motivational pace of motor output. Motor abnormalities are also a common feature of psychiatric i llness. Several subcortical limbic-motor entry points have been define d in recent years, but cortical entry points are understood poorly, de spite the fact that a part of the limbic robe, the cingulate motor cor tex (area 24c or M3, and area 23c or M4), contributes axons to the cor ticospinal pathway. Using retrograde and anterograde tracers in rhesus monkeys, we investigated the ipsilateral limbic input to area 24c and adjacent area 23c. Limbic cortical input to areas 24c and 23c arise f rom cingulate areas 24a, 24b, 23a, 23b, and 32, retrosplenial areas 30 and 29, and temporal areas 35, TF and TH. Areas 24c and 23c were also interconnected strongly. The dysgranular part of the orbitofrontal co rtex and insula projects primarily to area 24c while the granular part of the orbitofrontal cortex and insula projects primarily to area 23c . Afferents from cingulate area 25, the retrocalcarine cortex, tempora l pole, entorhinal cortex, parasubiculum, and the medial part of area TH target primarily or only area 24c. Our findings indicate that a var iety of telencephalic limbic afferents converge on cortex lining the l ower bank and fundus of the anterior part of the cingulate sulcus. Bec ause it is known that this cortex gives rise to axons ending in the sp inal cord, facial nucleus, pontine gray, red nucleus, putamen, and pri mary and supplementary motor cortices, we suggest that the cingulate m otor cortex forms a strategic cortical entry point for limbic influenc e on the voluntary motor system. (C) 1998 Elsevier Science Inc.