The reliability and clinical validity of functional magnetic resonance imaging in the assessment of language in pre-surgical patients with temporal lobe epilepsy

Defining language lateralisation is important to minimise morbidity in patients treatedsurgically for temporal lobe epilepsy (TLE). Functional magnetic resonance imaging(fMRI) offers a promising, non-invasive, alternative strategy to the Wada test. Here,fMRI has been used to study healthy controls and patients with TLE in order (i) todefine language-related activation patterns and their reproducibility; (ii) to comparelateralisation determined by fMRI with that from the Wada test; and (iii) to explore theusefulness of multiple fMRI language paradigms. 18 healthy controls (12 right-handedand 6 left-handed) and 24 pre-operative TLE patients (19 right-handed: 12 left-TLE, 7right-TLE; 5 left-handed: 2 right-TLE, 3 left-TLE) were studied using fMRI. Four fMRIlanguage paradigms used: phonetic and semantic fluency, and the naming of living andnon-living things. The data for all 4 tasks were acquired during a single scanningsession on two occasions. All patients also underwent Wada testing. In patients andcontrols, phonetic and semantic fluency tasks were robustly activating and stronglylateralising. Quantified language-related lateralisation from fMRI verbal fluency datawas highly reproducible and concordant with the lateralisation of the Wada test. Bothfluency tasks identified patients with atypical language lateralisation, including 4/12right-handed patients with left-TLE and 4/5 left-handed TLE patients, regardless of theside of epileptic focus. In comparison, the two confrontational naming tasks were notstrongly lateralising and did not reliably agree with Wada lateralisation in either 12right-handed controls or 19 right-handed patients with TLE. However, there was adifference in the pattern of fMRI activation in right-handed pat ients with left-TLE.Left-TLE patients had a more right lateralised network of activation when naming livingthings relative to non-living things, suggesting that some patients may be at risk of acategory specific naming decline for non-living things after left anterior temporallobectomy. These results demonstrate that non-invasive fMRI measures of languagerelatedlateralisation may provide a practical and reliable alternative to invasive testingfor pre-surgical language lateralisation in patients with TLE. The high proportion ofTLE patients showing atypical language lateralisation suggests considerable plasticityof language representation in the brains of patients with intractable TLE