Hippocampal formation involvement in a language-activation task in patients with mesial temporal lobe epilepsy

The study aims to explore the contribution of the hippocampal formation to the retained language-comprehension network in patients with unilateral mesial temporal lobe epilepsy (TLE).

We performed a functional magnetic resonance (MRI) study based on a language comprehension paradigm in 45 right-handed patients with unilateral mesial TLE and 35 healthy control subjects. Activations in the hippocampal formations in both hemispheres were analyzed for each subject as well as for groups of left TLE, right TLE, and controls.

In sum, 82% of TLE patients displayed hippocampal activations. A significant difference in hippocampal activation between left and right TLE was found: Right TLE patients showed increased activity in the left hippocampal formation compared with left TLE patients. In contrast, patients with left TLE did not show increased activity in the right hippocampal formation compared with right TLE patients. In comparison with a healthy control group, right TLE patients activated the left hippocampal formation to a greater extent, whereas patients with left TLE did not activate the right hippocampal formation to a greater degree. These findings point to an increased involvement of the left hippocampal formation during a language-comprehension task in right TLE patients. In contrast, left TLE in right-handed patients seems not associated with an enhanced involvement of the right hippocampal formation in retained language comprehension.

These findings suggest that effective language comprehension in right-handed subjects with TLE depends on the involvement of the left hippocampal formation and underline the risks of postoperative language decline in patients with left TLE.