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

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 fifty-one 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.

Saccade direction encoding in the primate entorhinal cortex during visual exploration

“…LD has reciprocal connections with posterior EC (20,21) and also projects densely to the presubiculum (22,23). The inferior parietal lobule (IPL), which contains cells with saccade-related activity, projects densely to the presubiculum and lightly to posterior EC (24,25). The presubiculum is known to send a massive projection to posterior EC (24).…”

“…The inferior parietal lobule (IPL), which contains cells with saccade-related activity, projects densely to the presubiculum and lightly to posterior EC (24,25). The presubiculum is known to send a massive projection to posterior EC (24). In view of these anatomical connections and the functional properties of neurons in LD and the IPL, information about eye position or saccades along preferred directions could reach posterior EC through direct input from LD and the IPL and indirectly through input from the presubiculum.…”

Ultra-high resolution in-vivo 7.0 T structural imaging of the human hippocampus reveals the endfolial pathway

“…This also allows for segmenting white matter of the hippocampus such as the stratum radiatum/lacunosum moleculare (Winterburn et al, 2013; Zeineh et al, 2012), which may aide in understanding different neurodegenerative diseases (Brickman et al, 2012). For all subfields of the hippocampal body, except the EF pathway, our work adheres to histologically outlined boundaries (Duvernoy, 2005; Insausti and Amaral, 2008) and thus we believe we can accurately segment out the hippocampus with our acquisition methodology. Our work adds to existing hippocampal subfield segmentation protocols by precisely defining the endfolial pathway, which should facilitate more detailed investigations of microstructure in the MTL.…”

“…Segmentation of hippocampal subregions was performed manually according to anatomic atlases and our prior work (Duvernoy, 2005; Insausti and Amaral, 2008; Yushkevich et al, 2009; Zeineh et al, 2012). Detailed hippocampal subfield segmentation was performed of the hippocampal body only, not the tail or head.…”

“…Subfields include the cornu ammonis regions (CA1, CA2, CA3 and CA4), the dentate gyrus (DG), and the subiculum, and these serve different functions and are variably affected by neurodegenerative diseases (Burggren et al, 2008; Mueller and Weiner, 2009). The CA fields consist of a pyramidal cell layer as well as the stratum radiatum (contains commissural fibers and schaffer collaterals, and apical dendrites of CA1/2/3 neurons), stratum lacunosum moleculare (contains schaffer collaterals and perforant pathway fibers and apical dendrites of CA1/2/3 neurons) and the stratum oriens (contains basal dendrites of pyramidal neurons, septal fibers and commissural fibers)(Insausti and Amaral, 2008). The medial and lateral entorhinal cortex sends projections to the dentate gyrus that perforate through the subiculum (Scher et al, 2007; Witter and Amaral, 1991) The dentate gyrus in turn sends unmyelinated projections called the mossy fibers that innervate the CA4 and CA3 pyramidal cells (Kondo et al, 2009).…”