MRI evidence for material‐specific encoding deficits and mesial‐temporal alterations in pre‐surgical frontal lobe epilepsy patients

Description: Anna Doll1, 2, Martin Wegrzyn2a, Friedrich G. Woermann1b, Kirsten Labudda1,2c, Christian G. Bien1d, & Johanna Kissler2, 3e 1 Bielefeld University, Medical School, Department of Epileptology (Krankenhaus Mara), Bielefeld, Germany; 2 Department of Psychology, Bielefeld University, Bielefeld, Germany; 3 Center for Cognitive Interaction Technology (CITEC), Bielefeld University, Bielefeld, Germany Introduction: Neuroimaging studies reveal frontal lobe contributions to memory encoding. Accordingly, patients with frontal lobe epilepsy (FLE) sometimes have memory impairments. Still, little is known about the structural or functional correlates of such impairments. Particularly, material-specific functional changes in cerebral activity during memory encoding in FLE are unclear. Methods: We compared 24 FLE patients undergoing pre-surgical evaluation (15 right, 8 left, 1 bilateral, 21 with established lesions) with 30 healthy controls on a memory fMRI-paradigm of learning scenes, faces, and words followed by an out-of-scanner recognition task as well as regarding their mesial temporal volumes. Further analyses addressed effects of FLE lateralization and performance level (normal versus low) and compared FLE patients with pre-existing data of temporal lobe epilepsy patients (TLE) from the same paradigm. Results: FLE patients had poorer memory performance than controls but were less impaired than TLE patients. FLE patients also had larger left hippocampal volumes than controls. These seemed, however, irrelevant or even dysfunctional with regard to memory performance. Further, we found functional changes in the mesial temporal lobes (mTLs) during encoding of all three materials, which were right-sided for scenes and faces and left-sided for words. In detail, during face encoding, FLE patients had generally decreased mTL activation, whilst during scene and in tendency word encoding low performing FLE patients had decreased mTL along with of decreased frontal activation. Intact verbal memory performance was associated with higher right mTL and frontal activation. Conclusion: At least pharmacoresistant FLE has a distinct functional and structural impact on the mTL. Effects vary with the encoded material and patients’ performance levels. The impact of FLE on memory performance and functional integrity is similar, but less severe than in TLE. Thus, in addition to the direct impact of the frontal lobe, memory impairment in FLE is presumably to a large part due to functional mTL changes triggered by disrupted frontal lobe networks.

Related article: http://doi.org/10.1002/epi4.12881