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Published on: August 11, 2015
Hippocampal subfield-specific connectivity findings in major depressive disorder: A 7 Tesla diffusion MRI study
John W Rutland1, Stephanie Brown1, Gaurav Verma1
1Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States.
Objective:
Diffusion magnetic resonance imaging (dMRI) enables non-invasive characterization of white matter (WM) structures in vivo. Prior studies suggest that certain WM tracts may be affected in major depressive disorder (MDD), however, hippocampal subfield-specific dMRI measures have not yet been explored in MDD. We use 7 Tesla dMRI to investigate differences in hippocampal subfield connectivity of MDD patients.
Methods:
Eighteen MDD patients and eighteen matched healthy volunteers underwent 7 Tesla MRI. The hippocampal formations were segmented by subfields and tractography was performed to determine streamline count (SC), fractional anisotropy (FA), and mean diffusivity (MD) in patients and controls. Significant subfield connectivity measures were also correlated with age at depression onset.
Results:
Compared with controls, MDD patients exhibited reduced SC in the molecular layer of the left dentate gyrus (p < 0.001). SC count in the left dentate gyrus was shown to positively correlate with age at disease onset (p < 0.05). Increased MD was observed in streamlines emanating from both the left (p = 0.0001) and right (p < 0.001) fimbriae in MDD patients.
Conclusions:
Increased MD of tracts in the fimbriae suggests compromised neuronal membranes in the major hippocampal output gate. Reduced SC of the dentate gyri indexes a disruption of normal cellular processes such as neurogenesis. These findings may have significant implications for identifying biomarkers of MDD and elucidating the neurobiological underpinnings of depression.
Insights
Major depressive disorder (MDD) patients show altered white matter connectivity in the hippocampus, specifically reduced streamline counts in the dentate gyrus and increased mean diffusivity in the fimbriae.
Area of Science:
- Neuroimaging
- Neuroscience
- Psychiatry
Background:
- Diffusion MRI (dMRI) non-invasively characterizes white matter (WM) in vivo.
- Previous research suggests WM tract alterations in major depressive disorder (MDD).
- Hippocampal subfield-specific dMRI measures in MDD remain underexplored.
Purpose of the Study:
- Investigate hippocampal subfield connectivity differences in MDD patients using 7 Tesla dMRI.
- Explore potential dMRI biomarkers for MDD.
Main Methods:
- Eighteen MDD patients and 18 healthy controls underwent 7 Tesla MRI.
- Hippocampal subfields were segmented; tractography assessed streamline count (SC), fractional anisotropy (FA), and mean diffusivity (MD).
- Connectivity measures correlated with age at depression onset.
Main Results:
- MDD patients had reduced left dentate gyrus SC (p < 0.001).
- Left dentate gyrus SC positively correlated with age at disease onset (p < 0.05).
- Increased MD in fimbriae streamlines (left: p = 0.0001; right: p < 0.001) was observed in MDD patients.
Conclusions:
- Increased fimbriae MD suggests compromised hippocampal output pathways in MDD.
- Reduced dentate gyrus SC may indicate disrupted neurogenesis or cellular processes.
- Findings offer potential biomarkers for MDD and insights into its neurobiology.
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