Evidence for direct projections from the basal nucleus of the amygdala to retrosplenial cortex in the Macaque monkey

The role of the primate retrosplenial cortex (RSC) in memory processing and spatial navigation has been well established. Recently, processing emotionally salient information has been attributed to the RSC as well. Little anatomical data, however, exist linking the RSC with known emotional processing centers within the brain. The amygdala has been implicated as a substrate for modulating memory for emotionally salient events; yet no study to date has demonstrated that this area has a direct connection in the primate brain. With modern retrograde tracer injections into the RSC and adjacent cortical areas of the monkey (Macaca fascicularis), we demonstrate that there are efferent projections from the basal nucleus of the amygdala to the RSC and area 31. These projections offer anatomical data supporting the hypothesis that the RSC might receive emotionally salient input directly from the amygdala and suggest a role for the RSC as a node within a neural system potentially capable of integrating emotional information for use in memory or other cognitive processes.