Semantic Functioning in Temporal Lobe Epilepsy: A Systematic Review and Meta-Analysis

Background: Despite the central role of the temporal lobes in conceptual processing, the impact of temporal lobe epilepsy (TLE) on semantic knowledge remains unclear. Objectives: This systematic review and meta-analysis aimed to investigate semantic functioning in TLE and the impact that seizure lateralisation and surgical intervention have on semantic outcomes. Methodology: A comprehensive literature search was conducted using Medline, Embase, and PsychINFO. Studies were eligible if they included participants aged ≥18 years with TLE and evaluated semantic functioning. Risk of bias was assessed using the Newcastle-Ottawa scale, and a narrative synthesis summarised the review findings. Meta-analyses compared semantic performance across individuals with TLE and healthy controls and left and right TLE. Results: 141 studies, encompassing 8,241 participants (TLE: n = 5,623, controls: n = 2,618), were included, reporting over 30 different semantic measures. Both narrative review and meta-analysis showed significantly poorer semantic performance in people with TLE compared to controls, with impairments in semantic fluency (g = -1.35), WAIS-IV Vocabulary (g = -1.08), and Camels and Cactus Test (g = -1.37), but not on Pyramids and Palm Trees (g = -0.44). Some lateralisation effects were evident, with verbal semantic impairments more prominent in left TLE. Conclusions: TLE is associated with a mild semantic impairment. While left-sided lesions are associated with worse verbal semantic impairment, lateralisation effects more broadly were mild and inconsistent. Our findings emphasise the need to conduct routine semantic assessments in TLE to support more precise cognitive deficit monitoring, better-informed surgical risk discussions, and the development of personalised rehabilitation plans.