Reciprocal anatomical connections between anterior thalamus and cingulate--retrosplenial cortex in the rabbit.

Reciprocal anatomical connections between posterior limbic (i.e. cingulate-retrosplenial) cortex and anterior thalamus in the rabbit were investigated using horseradish peroxidase histochemistry. Results showed that the cells of origin for corticofugal fibers are contained only within deep cortical layers, while thalamofugal projections terminate only within superficial laminae. That is, only layer VI neurons of cingulate-retrosplenial cortex project to thalamic regions, while cortical layers I and IV are the primary targets of thalamic afferents.