Organization of projections from the medial temporal cortical areas to the ventral striatum in macaque monkeys

Recent evidence on behaviors in macaque monkeys indicate that the medial temporal cortical areas such as the entorhinal cortex (EC), perirhinal cortex, and parahippocampal cortex (PHC) are importantly involved in limbic and sensory memory function. Neuroanatomical studies also have demonstrated that the medial temporal cortical areas are connected with the ventral striatum, although comparatively little is known about the precise topography of these connections. We investigated the topographic organization of connections between the medial temporal cortical areas and the ventral striatum by placing retrograde tracers into five different regions of the ventral striatum: the ventromedial caudate nucleus, ventral shell, central shell, dorsal core of the nucleus accumbens (NA), and ventrolateral putamen. We found that the shell of the NA was the main projection site from the medial temporal cortical areas. Within the shell of the NA, there were also differential connections: EC diffusely innervates shell of the NA, while the projections from the perirhinal cortex and PHC concentrate on the ventral shell of the NA. Taken together, it is possible that the ventral shell of the NA is the main integration site of the limbic and sensory memory coming from the EC, perirhinal cortex, and PHC.