Cortical projections of the non‐entorhinal hippocampal formation in the cynomolgus monkey (Macaca fascicularis)

Abstract

Episodic memory consolidation requires the integrity of the anatomical pathways between the cerebral cortex and the hippocampal formation. Whilst the largest cortical output of the hippocampal formation originates in the entorhinal cortex, direct projections from CA1, subiculum and presubiculum to the cortex have been reported. The aim of this study is the assessment of the extent, topography and relative strength of those projections, as a parallel/alternate route of memory processing. A total of 45 injections in 28 Macaca fascicularis monkeys were used. Cortical deposits of fluorescent tracers (20 cases, 3% Fast Blue, 2% Diamidino Yellow) or 1% WGA-HRP (eight cases) were made in different cortical areas of the frontal, temporal and parietal lobes, as well as cingulate cortex by direct exposure of the cortical surface. After appropriate survival, animals were perfused and the brains serially sectioned at 50 microm and the retrograde labelling charted with an X-Y digitizing system. Retrograde neuronal labelling was observed in CA1, subiculum, presubiculum and parasubiculum; it was absent in the dentate gyrus, CA3 and CA2. Compared to other portions of the hippocampal formation, the CA1-subiculum border had the highest number of labelled neurons (especially after deposits in the rostral perirhinal cortex), followed by medial frontal cortex, temporal pole, orbitofrontal, anterior and posterior cingulate cortices, parietal and inferotemporal cortices, and no labelling after posterior inferotemporal and lateral frontal cortices. Our results indicate that CA1, subiculum, presubiculum and parasubiculum send direct output to cortical areas. This nonentorhinal, hippocampal formation cortical output may be relevant in memory processing.

The increase in medial prefrontal glutamate/glutamine concentration during memory encoding is associated with better memory performance and stronger functional connectivity in the human medial prefrontal–thalamus–hippocampus network

“…The mPFC appears to serve as a critical hub obtaining, integrating and applying knowledge for long‐term use (Fernández, 2017). This role is supported by anatomical connections revealed in nonhuman primates and rodents showing that the mPFC receives unidirectional afferents from the hippocampus (Aggleton, Dumont, & Warburton, 2011; Insausti and Munoz, 2001; Barbas and Blatt, 1995) and in turn, has reciprocal connections to several thalamic nuclei including anterior, medial dorsal, and midline nuclei, which are indirectly or directly reciprocally connected to the hippocampus (Aggleton et al, 2011). Thus, the unidirectional connection from hippocampus to mPFC may be reciprocated via routes through the thalamus.…”

Working Memory for Social Cues Recruits Orbitofrontal Cortex and Amygdala: A Functional Magnetic Resonance Imaging Study of Delayed Matching to Sample for Emotional Expressions

“…Previous fMRI data has demonstrated a role for MTL structures, including the hippocampus and surrounding parahippocampal cortex, in the short term maintenance of novel information (Ranganath and D'Esposito, 2001;Stern et al, 2001;Ranganath et al, 2003Ranganath et al, , 2005Schon et al, 2004;Schon et al, 2005). Based on the rich connections between the hippocampus, amygdala, and OFC (Barbas, 2000;Insausti and Munoz, 2001;Munoz and Insausti, 2005), we suggest that together these areas form a circuit that binds together and actively maintains emotion and identity information in WM.…”

Does lateral parietal cortex support episodic memory?

“…Lateral posterior parietal cortex has reciprocal connections with entorhinal, parahippocampal, and hippocampal regions of the medial temporal lobe (Blatt et al, 2003;Clower et al, 2001;Insausti & Munoz, 2001;Laveneux et al, 2002;Munoz & Insausti, 2005;Rockland & Van Hoesen, 1999;Suzuki & Amaral, 1994), as well as with the medial parietal region (Kobayashi & Amaral, 2003;Morris et al, 1999b). It is also connected to anterior cingulate and dorsolateral prefrontal cortex, in particular BAs 6, 8, and 46 (Cavada & Goldman-Rakic, 1989;Lewis & Van Essen, 2000;Petrides & Pandya, 1984;Petrides & Pandya, 1999).…”

“…Given the clear correspondence between the neuroimaging and human lesion data concerning episodic and autobiographical memory, and the strong anatomical connections with medial temporal (Insausti et al, 1987;Insausti & Munoz, 2001;Kobayashi & Amaral, 2003;Morris et al, 1999a;Morris et al, 1999b;Suzuki & Amaral, 1994;Van Hoesen & Pandya, 1975) and dorsolateral prefrontal areas (Goldman-Rakic et al, 1984;Morris et al, 1999a;Petrides & Pandya, 1999;Kobayashi & Amaral, 2003) as well as the anterior and lateroposterior nuclei of the thalamus (Morris et al, 1999a), there is relatively little controversy that the medial parietal and caudomedial limbic areas are involved in episodic and autobiographical memory. For this reason, we will not discuss the medial regions further, and will focus on the lateral parietal region.…”