Memory fMRI lateralizes temporal lobe epilepsy

Background: The assessment of mesial temporal lobe (MTL) function is import ant for the diagnosis and treatment of temporal lobe epilepsy (TLE) and oth er brain diseases. Declarative memory depends on the integrity of the MTL r egion. Objective: To investigate hemispheric asymmetries of MTL activity in patients with symptomatic TLE. Methods: With use of blood oxygenation leve l-dependent fMRI, hemispheric asymmetries in MTL activation of 30 individua l patients with refractory symptomatic TLE and 17 healthy control subjects were studied. Activation was induced by a task employing mental navigation and recall of landmarks based on the retrieval of individually familiar vis uospatial knowledge. Results: The study demonstrated that the memory task u sed reliably activated MTL structures in individual control subjects and pa tients with refractory TLE including children, older subjects, and patients with low formal IQ. Interhemispheric differences in MTL activation lateral ized the side of seizure onset in 90% of patients with symptomatic unilater al TLE. In contrast, healthy control subjects did not show a systematic asy mmetry of MTL activation. Correlations between MTL activation and neuropsyc hological measures suggest that the fMRI-detectable MTL changes were specif ically related to memory rather than to memory-independent visuospatial abi lities. Conclusion: fl IRI of memory-induced MTL activation lateralizes the side of seizure onset in patients with refractory symptomatic TLE and may provide complementary information for presurgical evaluation.