White matter microstructure complements morphometry for predicting verbal memory in epilepsy.

Area of Science:

• Neuroscience
• Neurology
• Cognitive Science

Background:

• Verbal memory impairment is common in temporal lobe epilepsy (TLE).
• Hippocampal and temporal lobe damage contribute to memory deficits.
• The roles of white matter vs. gray matter and microstructural vs. morphometric measures in TLE memory impairment are not well understood.

Purpose of the Study:

• To determine whether microstructural (DTI) or morphometric (sMRI) measures of temporal lobe pathology are better predictors of verbal memory impairment in TLE.
• To assess the relative contributions of white matter and gray matter pathology to memory performance, controlling for hippocampal volume.

Main Methods:

• Diffusion tensor imaging (DTI) and structural MRI (sMRI) were used to assess temporal lobe pathology in 26 TLE patients and 35 controls.
• Verbal memory was evaluated using the Logical Memory (LM) subtest.
• Hierarchical regression analyses were performed to identify predictors of verbal memory performance.

Main Results:

• Impaired verbal recall in TLE patients was associated with increased mean diffusivity (MD) in temporal lobe white matter tracts.
• Microstructural white matter measures, specifically MD in the left inferior longitudinal fasciculus (ILF) and pericortical white matter, significantly predicted verbal recall after controlling for left hippocampal volume (HCV).
• A predictive model including left HCV and MD of the left ILF and pericortical white matter explained 60% of the variance in delayed recall.

Conclusions:

• White matter microstructure is a significant predictor of verbal memory impairment in TLE.
• Combining DTI and sMRI measures, particularly left HCV and specific white matter MD values, enhances the prediction of verbal memory deficits.
• These findings highlight the complementary roles of DTI and sMRI in understanding cognitive dysfunction in TLE and potentially other memory disorders.