Sparse asynchronous cortical generators can produce measurable scalp EEG signals.
We investigate to what degree the synchronous activation of a smooth patch of cortex is necessary for observing EEG scalp activity. We perform extensive simulations to compare the activity generated on the scalp by different models of cortical activation, based on intracranial EEG findings reported in the literature. The spatial activation is modeled as a cortical patch of constant activation or as random sets of small generators (0.1 to 3cm(2) each) concentrated in a cortical region. Temporal activation models for the generation of oscillatory activity are either equal phase or random phase across the cortical patches. The results show that smooth or random spatial activation profiles produce scalp electric potential distributions with the same shape. Also, in the generation of oscillatory activity, multiple cortical generators with random phase produce scalp activity attenuated on average only 2 to 4 times compared to generators with equal phase. Sparse asynchronous cortical generators can produce measurable scalp EEG. This is a possible explanation for seemingly paradoxical observations of simultaneous disorganized intracranial activity and scalp EEG signals. Thus, the standard interpretation of scalp EEG might constitute an oversimplification of the underlying brain activity.
Montreal Neurological Institute and Hospital, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada. Electronic address: nicolas.vonellenrieder@mcgill.ca.
Nicolás
N
von Ellenrieder
Montreal Neurological Institute and Hospital, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada; École Polytechnique, Université Libre de Bruxelles, 50 Avenue F. D. Roosevelt, 1050 Bruxelles, Belgium.
Jonathan
J
Dan
Department of Medicine, Center for Neuroscience Studies, Queen's University, 18 Stuart Street, Kingston, Ontario, K7L 3N6, Canada.
Birgit
B
Frauscher
Montreal Neurological Institute and Hospital, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada.
Jean
J
Gotman
D001683:Biological Clocks / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D063226:Central Pattern Generators / Q000502:physiology; D002540:Cerebral Cortex / Q000502:physiology*; D003198:Computer Simulation; D003344:Cortical Synchronization / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods*; D006801:Humans; D008959:Models, Neurological; D009415:Nerve Net / Q000502:physiology*; D015203:Reproducibility of Results; D012535:Scalp / Q000502:physiology*; D012680:Sensitivity and Specificity
Asynchronous activity; Boundary elements method; Cortical generators; Modeling; Scalp EEG