Spatial distribution of neuronal complexity loss in neocortical lesional epilepsies

Purpose: Nonlinear EEG analysis is valuable in characterizing the spatiotem poral dynamics of the epileptogenic process in mesial temporal lobe epileps y. We examined the ability of the measure neuronal complexity loss (L*) to characterize the primary epileptogenic area of neocortical lesional epileps ies during the interictal state. Methods: Spatial distribution of L* (L* map) was extracted from electrocort icograms (n = 52) recorded during presurgical assessment via subdural 64-co ntact grid electrodes covering lesions in either frontal, parietal, or temp oral neocortex in 15 patients. The exact location of recording contacts on the brain surface was identified by matching a postimplant lateral x-ray of the skull with a postoperatively obtained sagittal MRI scan. Reprojecting L* maps onto the subject's brain surface allowed us to compare the spatial distribution of L* with the resection range of the extended lesionectomy. Results: In each of the six patients who became seizure-free, maximum value s of L* were restricted to recording sites coinciding with the area of rese ction. In contrast, L* maps of most patients who had no benefit from the re section indicated a more widespread extent or the existence of additional, probably autonomous, foci. The mean of L* values obtained from recording si tes outside the area of resection correctly distinguished 13 patients (86.7 %) with respect to seizure outcome. Conclusions: Relevant information obtained from longlasting interictal elec trocorticographic recordings can be compressed to a single L* map that cont ributes to a spatial characterization of the primary epileptogenic area. In neocortical lesional epilepsies, L* allows for identification and characte rization of epileptogenic activity and thus provides an additional diagnost ic tool for presurgical assessment.