Topographic organization of the reciprocal connections between the monkey entorhinal cortex and the perirhinal and parahippocampal cortices

Abstract

The perirhinal and parahippocampal cortices constitute the major sources of cortical input to the monkey entorhinal cortex. Neuropsychological studies have shown that these three cortical regions contribute in an important way to normal memory function. We have investigated the topographic and laminar organization of the reciprocal projections between the entorhinal cortex and these two adjacent cortical areas by placing anterograde and retrograde tracers in all three regions. There were three major findings. First, the perirhinal and parahippocampal cortices have distinct but partially overlapping interconnections with the entorhinal cortex. The perirhinal cortex tends to be interconnected with the rostral two-thirds of the entorhinal cortex while the parahippocampal cortex tends to be interconnected with approximately the caudal two-thirds of the entorhinal cortex. Second, the degree of reciprocity of the interconnections of the entorhinal cortex with the perirhinal and parahippocampal cortices differs. The parahippocampal/entorhinal connections have a high degree of reciprocity. In contrast, the degree of reciprocity of the perirhinal/entorhinal interconnections varies depending on the mediolateral position within the perirhinal cortex; medial portions of the perirhinal cortex exhibit a higher degree of reciprocity with the entorhinal cortex than lateral portions. Third, the projections from the perirhinal and parahippocampal cortices to the entorhinal cortex resemble a feedforward projection, while the projections from the entorhinal cortex to the perirhinal and parahippocampal cortices resemble a feedback projection pattern.

Processing stages underlying word recognition in the anteroventral temporal lobe

“…Intracellular recordings show that the initial sink is due to monosynaptic EPSPs, and the later is due to polysynaptic EPSPs (Biella et al, 2001). Conversely, PR (BA36) projects widely to layer I in IT (Lavenex et al, 2002), and also within itself (Suzuki and Amaral, 1994). These studies suggest that the initial middle layer sink noted in the current study represents excitatory input from lower cortical areas; the following middle layer sink represents a period when the predominant excitatory input is feedforward; and the final superficial layer sink a period when top-down and local association afferents predominate.…”

Dissociation Between the Effects of Damage to Perirhinal Cortex and Area TE

“…Second, because humans with damage to the perirhinal cortex demonstrate normal visual perception as evidenced by intact visual recognition performance with very short delays (Buffalo et al 1998a), whereas area TE has been proposed to play a role in visual perceptual processing (Iwai and Mishkin 1968;Gross 1973;Dean 1976;Buffalo et al 1998b), we reasoned that the two areas might differ in their contributions to visual short-term memory and visual long-term memory. Third, the perirhinal cortex receives direct input from visual areas upstream from area TE (Suzuki and Amaral 1994a), and area TE does not project exclusively to the perirhinal cortex but also originates direct prefrontal and parietal cortical projections as well as subcortical projections to the caudate nucleus (Van Hoesen et al 1981;Saint-Cyr et al 1990;Webster et al 1994). Accordingly, we reasoned that it might be possible to demonstrate a dissociation between the effects of lesions of the perirhinal cortex and area TE on two tasks that involved different kinds of visual discrimination.…”

“…Area TE lies immediately adjacent and lateral to the perirhinal cortex and is considered to be the last exclusively visual area in the ventral visual processing stream (Ungerleider and Mishkin 1982). Area TE also originates strong anatomical projections to perirhinal cortex and receives projections from it (Suzuki and Amaral 1994a). With respect to the perirhinal cortex, studies in humans, monkeys, and rats have demonstrated that lesions of perirhinal cortex (or deactivation by cooling) impair performance on tests of learning and memory (Horel et al 1987;Bachevalier et al 1993;Mumby and Pinel 1994;Ennaceur et al 1996;Ennaceur and Aggleton 1997;Buffalo et al 1998a).…”

Formation of mnemonic neuronal responses to visual paired associates in inferotemporal cortex is impaired by perirhinal and entorhinal lesions.

“…There is strong evidence that IT cortex receives direct and indirect backward projections from the perirhinal and entorhinal cortex (10)(11)(12)(13). The hypothesis for the role of the backward connections predicts that the lesion of the perirhinal and entorhinal cortex would impair the formation of the associative code for pictures in the IT cells.…”