Projections from the cingulate cortex in the rat

Abstract

The efferent connections of the cingulate cortex were studied in the rat by tracing the axon degeneration elicited by small lesions in the cingulate region. Conclusions were as follows. Projections to the thalamus. The retrosplenial granular region of the posterior cingulate cortex projects to the anteroventral thalamic nucleus (AV) whereas the dorsally adjoining agranular retrosplenial field projects to the laterodorsal nucleus. The anteromedial (AM) nucleus may have a diffuse relation to the cingulate cortex; it appears to receive projections from both anterior and posterior cingulate subfields. No evidence of a significant cortico-thalamic relationship of the anterodorsal nucleus (AD) was found. The greater part of the anterior cingulate cortex projects to the mediodorsal nucleus (MD); the more rostral and ventral regions of the pregenual cortex in addition project to the ventromedial nucleus (VM). Projections to the brain stem. All regions of the cingulate cortex project to the caudate nucleus, zona incerta, pretectal area, central gray substance, midbrain tegmentum, and pontine nuclei. No evidence of cingulate projections to characteristically ‘limbic’ regions of the subcortex — such as the septal region, the hypothalamus and associated regions of the midbrain tegmentum — could be found. Instead, the brain stem projections of the cingulate cortex widely overlap those originating in cortical regions which are generally interpreted as ‘somatic sensori-motor’. Thus, the cingulate cortex appears as a vast and differential neural mechanism receiving major impulse afflux from the limbic system by way of the anterior and laterodorsal thalamic nuclei, and exerting its influence primarily upon brain structures not directly involved in any of the currently recognized limbic circuits.