Entorhinal cortex of the monkey: IV. Topographical and laminar organization of cortical afferents

Authors

  • Ricardo Insausti,

    1. Laboratory of Human Neuroanatomy, Department of Health Sciences and CRIB, School of Medicine, University of Castilla-La Mancha, 02006 Albacete, Spain
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  • David G. Amaral

    Corresponding author
    1. Department of Psychiatry and Behavioral Sciences, The M.I.N.D. Institute, Center for Neuroscience and the California National Primate Research Center, University of California Davis, Davis, California 95616
    • The M.I.N.D. Institute, UC Davis, 2825 50th Street, Sacramento, CA 95817
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  • The authors dedicate this paper to the memory of W. Maxwell (Max) Cowan, who was a mentor and friend to both of the authors. Max initiated this series of studies and carefully shepherded the initial projects through design, implementation, and publication. We learned much from Max and think of him often as we continue our quest to understand the organization of the hippocampal formation.

Abstract

The nonhuman primate entorhinal cortex is the primary interface for information flow between the neocortex and the hippocampal formation. Based on previous retrograde tracer studies, neocortical afferents to the macaque monkey entorhinal cortex originate largely in polysensory cortical association areas. However, the topographical and laminar distributions of cortical inputs to the entorhinal cortex have not yet been comprehensively described. The present study examines the regional and laminar termination of projections within the entorhinal cortex arising from different cortical areas. The study is based on a library of 51 3H-amino acid injections that involve most of the afferent regions of the entorhinal cortex. The range of termination patterns was broad. Some areas, such as the medial portion of orbitofrontal area 13 and parahippocampal areas TF and TH, project widely within the entorhinal cortex. Other areas have a more focal and regionally selective termination. The lateral orbitofrontal, insular, anterior cingulate, and perirhinal cortices, for example, project only to rostral levels of the entorhinal cortex. The upper bank of the superior temporal sulcus projects mainly to intermediate levels of the entorhinal cortex, and the parietal and retrosplenial cortices project to caudal levels. The projections from some of these cortical regions preferentially terminate in the superficial layers (I–III) of the entorhinal cortex, whereas others project more heavily to the deep layers (V–VI). Thus, some of the cortical inputs may be more influential on the cortically directed outputs of the hippocampal formation or on gating neocortical information flow into the other fields of the hippocampal formation rather than contributing to the perforant path inputs to other hippocampal fields. J. Comp. Neurol. 509:608–641, 2008. © 2008 Wiley-Liss, Inc.

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