Cortico-hippocampal networks underpin verbal memory encoding in temporal lobe epilepsy

Area of Science:

• Neuroscience
• Neuroimaging
• Epilepsy Research

Background:

• Human verbal memory's structural basis remains poorly understood, hindering clinical management of verbal memory impairment.
• A finer anatomical understanding of the verbal memory network is clinically significant for patients with memory deficits.

Purpose of the Study:

• To investigate the contributions of cerebral cortex and hippocampal subfields to verbal memory encoding in temporal lobe epilepsy (TLE).
• To assess the association between grey matter volume in specific brain regions and verbal learning performance in TLE patients.

Main Methods:

• A cross-sectional study involving 84 TLE patients with hippocampal sclerosis (HS) and 43 healthy controls.
• High-resolution MRI scans were used to extract morphometric and volumetric measures of the cerebral cortex and hippocampal subfields.
• Standardized neuropsychological evaluation, including verbal memory tests, was conducted, with performances analyzed as Z-scores.

Main Results:

• Reduced grey matter volume in the medial and dorsolateral prefrontal cortex, superior and middle temporal gyri, cingulate cortex, ventrolateral prefrontal cortex, and parietal-temporal-occipital junction correlated with worse verbal learning.
• Smaller volumes in the left dentate gyrus, cornu ammonis 4, and cornu ammonis 3 were associated with poorer verbal learning Z-scores.
• These associations were consistent in the overall cohort and in a subgroup of HS patients.

Conclusions:

• Verbal learning in TLE patients is significantly related to the volume of specific prefrontal, temporal, and cingulate cortical regions, as well as left dentate gyrus, cornu ammonis 4, and cornu ammonis 3 hippocampal subfields.
• The study suggests a corticohippocampal network underlying verbal learning in TLE, enhancing the understanding of human verbal memory.
• Identified biomarkers may guide future therapeutic interventions and inform surgical strategies to preserve verbal memory function.