Language impairment in temporal lobe epilepsy: insights from a meta-analysis of fMRI studies

Temporal lobe epilepsy (TLE) is frequently associated with language impairment. This meta-analysis quantitatively synthesized data from 12 functional neuroimaging studies, including 390 TLE patients and 356 healthy controls (age range: 8.1-70 years; 57.2 % female), to identify language-related brain alterations in TLE. Compared to healthy controls, TLE patients exhibited hypoactivity within the left frontal language regions, including Broca's area, precentral gyrus, and middle frontal gyrus, suggesting language impairment across syntactic, semantic, and articulatory processes. In parallel, hyperactivity in right-hemisphere regions was observed, reflecting compensatory neuroplastic adaptations to left-hemisphere language dysfunction. This reorganization may partially preserve language function but also indicate language processing inefficiencies. Moderator analyses revealed that in TLE, language comprehension compared with vocabulary elicited occipital hyperactivity and inferior frontal hypoactivity, reflecting posterior compensation and reduced frontal control. Left-sided TLE, compared to right-sided TLE, was more associated with hypoactivity in Broca's area, reflecting the heightened vulnerability of the language-dominant frontotemporal regions. Greater hyperactivity in the right superior temporal gyrus with longer TLE duration may imply sustained compensatory engagement, whereas diminished hyperactivity in the right hippocampal gyrus with TLE duration may indicate a decline in compensatory capacity due to epileptic disruption. Furthermore, the more severity of language impairment correlated with (1) hypoactivity in Broca's area, suggesting its role as a neural marker of language dysfunction, and (2) hyperactivity in the left insula, representing neural inefficiency or maladaptive neuroplastic reorganization. Collectively, these findings emphasize the complex interactions between epileptic pathology, compensatory reorganization, and progressive neuroplastic adaptation in shaping language outcomes in TLE.