Uncovering a Role for the Dorsal Hippocampal Commissure in Recognition Memory

Abstract

The dorsal hippocampal commissure (DHC) is a white matter tract that provides interhemispheric connections between temporal lobe brain regions. Despite the importance of these regions for learning and memory, there is scant evidence of a role for the DHC in successful memory performance. We used diffusion-weighted magnetic resonance imaging (DW-MRI) and white matter tractography to reconstruct the DHC in both humans (in vivo) and nonhuman primates (ex vivo). Across species, our findings demonstrate a close consistency between the known anatomy and tract reconstructions of the DHC. Anterograde tract-tracer techniques also highlighted the parahippocampal origins of DHC fibers in nonhuman primates. Finally, we derived diffusion tensor MRI metrics from the DHC in a large sample of human subjects to investigate whether interindividual variation in DHC microstructure is predictive of memory performance. The mean diffusivity of the DHC correlated with performance in a standardized recognition memory task, an effect that was not reproduced in a comparison commissure tract—the anterior commissure. These findings highlight a potential role for the DHC in recognition memory, and our tract reconstruction approach has the potential to generate further novel insights into the role of this previously understudied white matter tract in both health and disease.

White Matter Dissection of the Fetal Brain

“…The fornix is involved in spatial processing and episodic memory ( Dumont et al, 2015 ; Hodgetts et al, 2015 ; Senova et al, 2020 ), as well as pattern separation ( Bennett et al, 2015 ). There is also emerging evidence of the dorsal hippocampal commissure contributing to recognition memory ( Postans et al, 2020 ). The anterior commissure’s functional implications in humans are still somewhat elusive, appearing to be related to olfactory and non-visual interhemispheric communication ( Gerrish et al, 2014 ).…”

Hippocampus co-atrophy pattern in dementia deviates from covariance patterns across the lifespan

“…thalamus, caudate nuclei) and additionally with the parieto-occipital fissure. Anatomically those associated brain regions were reminiscent to some extent to the grey matter regions around the dorsal hippocampal commissure, being connected with posterior cingulum, tapetum, and fornix (Postans et al, 2019). The dorsal hippocampal commissure is associated with learning, memory and recently also with recognition (Postans et al, 2019).…”

“…Anatomically those associated brain regions were reminiscent to some extent to the grey matter regions around the dorsal hippocampal commissure, being connected with posterior cingulum, tapetum, and fornix (Postans et al, 2019). The dorsal hippocampal commissure is associated with learning, memory and recently also with recognition (Postans et al, 2019). The fornix is the white matter output of the hippocampus through the tail (Amaral et al, 2018) whereas the tapetum transfers information between hemispheres.…”

Loss of Ryanodine Receptor 2 impairs neuronal activity-dependent remodeling of dendritic spines and triggers compensatory neuronal hyperexcitability

“…Moreover, in our study RyR2 knockout affected predominantly maintenance of dendritic spines of basal dendrites, which are a key recipient of the commissural input from the contralateral hemisphere [ 64 ]. Thus, RyR2 may be linked to synaptic homeostasis required for cross-hemispheric transfer of memory-relevant information [ 65 , 66 ]. Along these lines, the dendritic structural sparsification that we found in response to RyR2 deletion was reliably observed in both, human neurodegenerative diseases [ 67 – 69 ] and animal models [ 42 , 70 – 72 ].…”