Abstract
The hippocampus is a key component of emotional and memory circuits and is broadly connected throughout the brain. We tracked the whole-brain connections of white matter fibres from the hippocampus using ultra-high angular resolution diffusion MRI in both a single 1150-direction dataset and a large normal cohort (n = 94; 391-directions). Using a connectomic approach, we identified six dominant pathways in terms of strength, length and anatomy, and characterised them by their age and gender variation. The strongest individual connection was to the ipsilateral thalamus. There was a strong age dependence of hippocampal connectivity to medial occipital regions. Overall, our results concur with preclinical and ex-vivo data, confirming that meaningful in vivo characterisation of hippocampal connections is possible in an individual. Our findings extend the collective knowledge of hippocampal anatomy, highlighting the importance of the spinal-limbic pathway and the striking lack of hippocampal connectivity with motor and sensory cortices.
Highlights
The impact of the hippocampus on various illness states may be as much a matter of “integrity” of connections as volume changes or morphometry
We are unaware of any published study that has conducted an unconstrained high angular resolution diffusion MRI (dMRI)-tractography of the hippocampal formation
We present the most comprehensive, highest angular resolution map of macroscopic hippocampal connections to date
Summary
The impact of the hippocampus on various illness states may be as much a matter of “integrity” of connections as volume changes or morphometry. One recent study presented dMRI tractography of the human Papez circuit in considerable detail[13], demonstrating connections among hubs in the MTL, retrosplenial gyrus, hippocampus, mammillary bodies, and anterior thalamic nuclei. Together, these advances permit investigation of hippocampal connections in humans at a previously unseen level of detail
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