The human dorsal hippocampal commissure: Delineating connections across the midline using multi-modal neuroimaging in...

Area of Science:

• Neuroscience
• Neuroimaging
• Human Brain Anatomy

Background:

• The dorsal hippocampal commissure (DHC) is a crucial white matter tract connecting the hippocampi.
• Its role and connectivity in humans, particularly in relation to other limbic structures, are not fully understood.
• Major Depressive Disorder (MDD) is associated with alterations in brain connectivity, but the DHC's involvement remains unexplored.

Purpose of the Study:

• To investigate the detailed anatomical connectivity of the human dorsal hippocampal commissure (DHC).
• To explore potential differences in DHC structure between healthy controls and patients with Major Depressive Disorder (MDD).
• To identify the specific brain regions connected by the DHC.

Main Methods:

• High-resolution T1/T2 MRI and High Angular Resolution Diffusion Imaging (HARDI) with Constrained Spherical Deconvolution (CSD) tractography were employed.
• Anatomically derived protocols were used to isolate the DHC.
• Segmentation of temporal pole, amygdala, hippocampus, and parahippocampal gyrus volumes was performed.

Main Results:

• The DHC connects not only the hippocampi but also links each hippocampus to the contralateral temporal pole, amygdala, and parahippocampal gyrus.
• The parahippocampal gyrus was the largest contributor to the DHC's volume.
• No significant effects of aging or sex on DHC integrity were observed in either group.
• No significant differences in DHC structure were found between healthy controls and MDD patients.

Conclusions:

• The human DHC facilitates complex interhemispheric communication involving the hippocampus, amygdala, temporal pole, and parahippocampal gyrus.
• The parahippocampal gyrus plays a significant role in DHC-mediated contralateral limbic system influence.
• This study provides the first investigation of the DHC in MDD and establishes its broader connectivity profile in the human brain.