Neuropsychological correlations with fornix and hippocampus in temporal lobe epilepsy demonstrated with diffusion...

Memory dysfunction is a common disabling comorbidity in temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS). While bilateral fornix diffusion abnormalities have been reported in TLE using diffusion tensor imaging (DTI), the impact of fornix pathology on cognitive outcomes remains unclear. This study investigated the relationships between fornix DTI, hippocampal volume, and cognitive outcomes in TLE.

Thirty-five TLE patients (21 unilateral HS, 11 non-HS, 3 bilateral HS) and 22 controls underwent fornix FLAIR-DTI (1.2 × 1.2 × 2 mm³ resolution) and hippocampal DTI (1 × 1 × 1 mm³) scans. Deterministic tractography was used to extract left and right fornix diffusion metrics including fractional anisotropy (FA). Whole hippocampi were manually segmented to yield volume and mean diffusivity (MD). In a subset of 23 TLE patients, linear correlations were assessed for verbal memory, non-verbal memory, and processing speed index (PSI) versus imaging measurements.

In the HS group, a significant linear correlation was found between both hippocampal volume (r = 0.58, p = 0.001) and MD (r = -0.42, p = 0.03) with fornix FA. Left hippocampal volume correlated with verbal memory (r = 0.74, p = 0.0001) but not with PSI (p > 0.05). Left fornix FA also correlated with verbal memory (r = 0.48, p = 0.025). In contrast, right hippocampal volume and right fornix FA showed no correlation with non-verbal memory (p > 0.05). FA of both left and right fornix correlated with PSI (left: r = 0.45, p = 0.038; right: r = 0.44, p = 0.037).

The findings of correlations between the hippocampus and memory, but not processing speed, and fornix with both memory and processing speed in TLE suggest a specialized role of the hippocampus in memory and a broader role for the fornix in cognitive function, beyond its association with memory.

The hippocampus is a brain structure involved in learning and memory. Patients with temporal lobe epilepsy (TLE), especially those with damage to the hippocampus, often experience memory and thinking problems. This study used advanced brain magnetic resonance imaging (MRI) to explore the role of a nearby structure called the fornix, which connects the hippocampus to other brain areas. We found that damage to both the hippocampus and fornix was linked to poor verbal memory, while damage to the fornix also affected thinking speed. These findings suggest that the fornix plays a broader role in brain function than previously thought.