Functional correlates of memory encoding in frontal versus temporal lobe epilepsy

Description: Temporal lobe epilepsy (TLE) and frontal lobe epilepsy (FLE) patients are prone to memory deficits and have structural and encoding-related cerebral alterations. To increase specificity of previous findings we directly compared 56 (25 right) TLE and 24 FLE patients regarding memory performance, hippocampal volumes and activation in a memory fMRI-paradigm of learning scenes, faces, and words followed by an out-of-scanner recognition task. Behaviourally, TLE and FLE patients were similarly impaired in recognition of scene, faces and words. In verbal free-recall measures, however, left-sided TLE performed worse, whilst in figural free-recall right-sided TLE performed worse than FLE patients. Structural data revealed smaller hippocampal volumes ipsilateral to seizure origin in TLE than FLE patients. Functional encoding-related hemodynamic activity showed that left-sided TLE had ipsilaterally less mesio-temporal activation during scene and face encoding than FLE patients. Conversely, FLE had stronger right-sided frontal activation during word encoding than right-sided TLE patients. The degree of deactivation of default-mode-network regions was largely similar, except that right-sided TLE had less deactivation of the left superior and middle temporal gyrus than FLE patients. Overall, the data underline the shared impact of TLE and FLE on fronto-temporal networks but also point towards task- and material-specific differences.