Idiomatic expressions (IE) and metaphors are a subdomain of pragmatic language whose interpretation differs from the literal meaning of individual words. Temporal lobe epilepsy (TLE) can affect pragmatic language, but some patients retain these abilities. This functional magnetic resonance imaging (fMRI) study investigates the neural networks involved in idioms comprehension in patients with drug resistant TLE compared to healthy controls.

Data from 32 patients with focal TLE (left or right) and 17 healthy volunteers were analyzed during an IE comprehension task using fMRI. Regions of Interest (RoIs) were identified from the activated areas in fMRI to analyze functional connectivity.

All participants completed the task successfully. Neuroimaging revealed a bilateral fronto-temporal network, lateralized to the right, involved in processing IE in the overall sample. Compared to controls, patients additionally activated frontal, temporal, and insular areas in both hemispheres. Controls exhibited fewer connections but greater inhibitory connectivity, while the opposite (more connections and increased excitatory connectivity) occurred in patients.

Patients with epilepsy not only recruited additional areas in the fMRI compared to controls, but also exhibited altered patterns of connectivity. Controls exhibited more effective inhibitory connectivity, with more modular RoIs. In contrast, patients demonstrated greater excitatory connectivity, suggesting compensatory neural recruitment in additional areas. These exacerbated connections may reflect the need to recruit alternative regions for pragmatic language comprehension, resulting in higher costs and lower efficiency.