In-depth human brain mapping: systematic and personalized investigation of multiple functional networks with intra-cerebral EEG
Introduction
In the last ten years, intra-cerebral EEG cognitive studies in epileptic patients have revealed that local, task-induced energy variations in the gamma band (above 40 Hz) are precise temporal and spatial markers of the neural networks underlying human cognition. In this paper, we propose a novel procedure which combines both offline and online gamma band measurements to provide detailed and extensive functional mapping in patients prior to surgery.
Section snippets
Methods
Each patient is recorded in a series of short (less than 10 minutes) cognitive tasks (‘localizers’). Each localizer is designed to bring into play a specific function, such as verbal working memory, or reading. Data analysis has been optimized so that any recording site showing task-related gamma band activations in a speficic task can be revealed in a matter of hours, at the very beginning of the patient's hospitalization. Because each recording site can be related so fast to precise cognitive
Results
The procedure has been sucessfully applied in a first group of patients. For each patient, our approach has revealed clear functional segragation of task-related gamma band actiivity, for instance between regions of the superior temporal sulcus responding to music and to speech, or portions of the fusiform gyrus responding to letters and to faces. Further, real-time analysis has proven extremely valuable to refine the functional hypothesis about task-sensitive regions: for instance, portions of
Conclusions
We propose a novel approach that is halfway between standard cognitive neuroimaging and bed-side neuropsychological testing procedures. The investigation is both systematic (because the same localizers are performed by all patients) and personalized (because subsequent real-time investigation in each patient depends on the results of the localizer studies). This approach yields an in-depth picture of the functional organization of each patient's brain, of direct interest in view of surgery; and