Thalamocingulate Connections in the Monkey

Abstract All cortical areas make massive reciprocal connections with the dorsal thalamic nuclei and because the great majority of subcortical inputs to the cortex originate from the dorsal thalamic nuclei, many believe that these thalamocortical inputs are essential for normal cortical functions. Although it remains unclear how they specifically contribute to cortical function, it has been suggested that they operate both as a way station for transmitting information from subcortical regions to the cortex (Sherman and Guillery, 2001) and as an “indirect relay” station for communicating information between different cortical regions (Rouiller and Welker, 2000). Regardless of which of these two modes is operative, the dorsal thalamic nuclei do not merely transfer information to the cortex, but they are an active integrator or modulator of information that is essential for normal cortical function. To this end, it is an essential prerequisite to know the details of the underlying connectivity between the dorsal thalamus and cortex.The cingulate cortex consists of four major regions (ordered posterior to anterior): posterior cingulate cortex (PCC), retrosplenial cortex (RSC), midcingulate cortex (MCC), and anterior cingulate cortex (ACC; Chapters 1, 3, 13; Vogt, 1993: Vogt et al., 2004, 2005). These four divisions are comprised of more than 20 different cortical areas that lie within the cingulate gyrus and the banks of the adjoining cingulate and callosal sulci in monkeys and humans. Recent anatomical studies using axonal transport methods in monkeys have uncovered a rough picture of thalamocingulate connectivity—each cingulate area has connections with a different set of thalamic nuclei as discussed in this chapter. These thalamic nuclei represent not only associational and midline/intralaminar thalamic nuclei but also parts of the motor and sensory thalamic nuclei. We must bear in mind that many more connections remain to be elucidated for most cingulate areas. For detailed cytoarchitecture and nomenclature of the monkey dorsal thalamus, the reader should consult the textbooks of Jones (1985, 1998) and Steriade et al. (1997).