Figure 2.

The anatomy of the medial temporal lobe memory system (Eichenbaum, 2000). In both monkeys and rats the origins of specific information to the hippocampus include virtually every neocortical association area. Each of these neocortical areas (blue) projects to one or more subdivisions of the parahippocampal region, which includes the perirhinal cortex (purple), the parahippocampal (or postrhinal) cortex (dark purple), and the entorhinal cortex (light purple; Burwell et al, 1995; Suzuki, 1996). The subdivisions of the parahippocampal region are interconnected and send major efferents to multiple subdivisions of the hippocampus itself (green), the dentate gyrus, the CA3 and CA1 areas, and the subiculum. Thus, the parahippocampal region serves as a convergence site for cortical input and mediates the distribution of cortical afferents to the hippocampus. Within the hippocampus, there are broadly divergent and convergent connections that could mediate a large network of associations (Amaral and Witter, 1989). The outcomes of hippocampal processing are directed back to the parahippocampal region, and the outputs of that region are directed in turn back to the same areas of the cerebral cortex that were the source of inputs to this region (Burwell et al, 1995; Suzuki, 1996). There are additional structures that have been included as components of this system, including medial diencephalic structures that connect with the hippocampus along with other subcortical areas, through a major fiber bundle called the fornix (Aggleton and Brown, 1999).