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Investigations on Alterations of Hippocampal Circuit Function Following Mild Traumatic Brain Injury
Published on: November 19, 2012
Microstructural Integrity of Hippocampal Subregions Is Impaired after Mild Traumatic Brain Injury
Sandra E Leh1, Clemens Schroeder1, Jen-Kai Chen2,3
11 Institute for Regenerative Medicine, University of Zurich , Switzerland .
Abstract:
Mild traumatic brain injury (mTBI) affects a large number of individuals and diffusion tensor imaging can be used to investigate microstructural integrity of brain tissue after mTBI. However, results have varied considerably between studies and gray matter (GM) integrity has been largely neglected in these investigations. Given impaired working memory processing after mTBI and its possible association with Alzheimer's disease, we investigated hippocampal integrity and parcellated this structure into five subregions: subiculum, cornu ammonis (CA) 1, CA 2/3, CA 4/dentate gyrus, and stratum radiatum/lacunosum-moleculare. We also employed shape analysis of bilateral hippocampi to explore whether morphological changes had occurred due to the traumatic injury and conducted neuropsychological memory tests. The sample comprised 15 subjects with mTBI (18-55 years, nine female) and 13 age- and sex-matched healthy control subjects (19-57 years, nine female). Voxelwise analyses showed significantly increased mean diffusivity in patients, compared with controls, in the right hippocampus and three of its five subregions (family-wise error corrected p < 0.05). Additionally, results from probabilistic tractography indicated impaired CA 1 connectivity after mTBI (Benjamini-Hochberg false discovery rate [FDR] corrected p < 0.05). Shape of bilateral hippocampi did not significantly differ between groups (Benjamini-Hochberg FDR corrected p > 0.05). Subjects with mTBI reported more symptoms and performed worse in a non-standard verbal working memory task. Based on these preliminary findings, we were able to demonstrate altered diffusivity of hippocampal subregions following mTBI, indicating impaired GM microstructural integrity. These differences highlight the potential of diffusion imaging for investigation of subtle yet relevant changes in GM microstructure not detected otherwise following mTBI.
Insights
Diffusion tensor imaging revealed impaired gray matter microstructure in the hippocampus of individuals with mild traumatic brain injury (mTBI). These findings highlight subtle changes in brain tissue integrity following mTBI.
Area of Science:
- Neuroimaging
- Neuroscience
- Radiology
Background:
- Mild traumatic brain injury (mTBI) impacts many individuals, with diffusion tensor imaging (DTI) used to assess brain microstructural integrity.
- Gray matter (GM) integrity post-mTBI has been understudied, despite potential links to cognitive deficits and Alzheimer's disease.
- Hippocampal integrity is crucial for memory functions often impaired after mTBI.
Purpose of the Study:
- To investigate hippocampal microstructural integrity and morphological changes in individuals with mTBI using DTI and shape analysis.
- To examine specific hippocampal subregions (subiculum, CA1, CA2/3, CA4/DG, SR/SLM) for alterations.
- To correlate imaging findings with neuropsychological memory test performance.
Main Methods:
- Recruited 15 mTBI patients and 13 healthy controls (ages 18-57).
- Utilized voxelwise DTI analysis to compare mean diffusivity (MD) between groups.
- Employed probabilistic tractography for connectivity assessment and hippocampal shape analysis.
- Administered neuropsychological tests, including a verbal working memory task.
Main Results:
- Significantly increased MD in the right hippocampus and three subregions in mTBI patients compared to controls (family-wise error corrected p < 0.05).
- Impaired CA1 connectivity identified in mTBI patients (Benjamini-Hochberg FDR corrected p < 0.05).
- No significant differences in hippocampal shape between groups (Benjamini-Hochberg FDR corrected p > 0.05).
- mTBI group reported more symptoms and poorer performance on a verbal working memory task.
Conclusions:
- DTI can detect altered diffusivity in hippocampal subregions, indicating impaired GM microstructural integrity following mTBI.
- These findings demonstrate subtle yet significant microstructural changes in gray matter not detectable by other methods.
- The study highlights the potential of DTI for investigating mTBI-related brain changes, particularly in the hippocampus.
