Human intracranial EEG (iEEG) recordings are primarily performed in epileptic patients for presurgical mapping purpose. When patients perform cognitive tasks, iEEG signals reveal high-frequency neural activities (HFA, between 40 Hz and 150 Hz) with exquisite anatomical, functional and temporal specificity. Such HFA were originally interpreted in the context of perceptual or motor binding, in line with animal studies on gamma-band (‘40Hz’) neural synchronization. Today, our understanding of HFA has evolved into a more general index of cortical processing: task-induced HFA would reveal, with excellent spatial and time resolution, the participation of local neural ensembles to the task-at-hand and the neural communication mechanisms allowing them to do so. This review promotes the claim that studying HFA with iEEG provides insights into the neural bases of cognition that cannot be derived as easily from other approaches, such as fMRI. We provide a series of examples supporting that claim, drawn from studies on memory, language and default-mode networks, and succesful attempts of real-time functional mapping.
Jean-Philippe LACHAUX, CRNL/Dycog