The Impact of Cerebral Source Area and Synchrony on Recording Scalp Electroencephalography Ictal Patterns

• Published in: Epilepsia (Copenhagen) 2007-11, Vol.48 (11), p.2167-2176
• Main Authors: Tao, James X., Baldwin, Maria, Ray, Amit, Hawes‐Ebersole, Susan, Ebersole, John S.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Biological and medical sciences; Brain Mapping - methods; Cerebral Cortex - physiopathology; Cortical sources; Cortical Synchronization - methods; Cortical Synchronization - statistics & numerical data; Drug toxicity and drugs side effects treatment; Electrodes, Implanted; Electroencephalography - methods; Electroencephalography - statistics & numerical data; Epilepsy, Temporal Lobe - diagnosis; Epilepsy, Temporal Lobe - physiopathology; Epilepsy, Temporal Lobe - surgery; Female; Functional Laterality - physiology; Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy; Humans; Intracranial EEG; Investigative techniques, diagnostic techniques (general aspects); Male; Medical sciences; Middle Aged; Nervous system; Nervous system (semeiology, syndromes); Neurology; Pharmacology. Drug treatments; Preoperative Care; Radionuclide investigations; Scalp EEG; Seizure generator; Seizure onset; Subdural electrodes; Subdural Space; Temporal Lobe - physiopathology; Temporal lobe epilepsy; Toxicity: nervous system and muscle
• ISSN: 0013-9580; 1528-1167
• DOI: 10.1111/j.1528-1167.2007.01224.x

Summary Purpose: To determine the cerebral electroencephalography (EEG) substrates of scalp EEG seizure patterns, such as source area and synchrony, and in so doing assess the limitations of scalp seizure recording in the localization of seizure onset zones in patients with temporal lobe epilepsy. Methods: We recorded simultaneously 26 channels of scalp EEG with subtemporal supplementary electrodes and 46–98 channels of intracranial EEG in presurgical candidates with temporal lobe epilepsy. We correlated intracranial EEG source area and synchrony at seizure onset with the corresponding scalp EEG. Eighty‐six simultaneous intracranial‐ and scalp‐recorded seizures from 23 patients were evaluated. Results: Thirty‐four intracranial ictal discharges (40%) from 9 patients (39%) had sufficient cortical source area (namely > 10 cm2) and synchrony at seizure onset to produce a simultaneous or nearly simultaneous focal scalp EEG ictal pattern. Forty‐one intracranial ictal discharges (48%) from 10 patients (43%) gradually achieved the necessary source area and synchrony over several seconds to generate a scalp EEG ictal pattern. These scalp rhythms were lateralized, but not localizable as to seizure origin. Eleven intracranial ictal discharges (13%) from 4 patients (17%) recruited the necessary source area, but lacked sufficient synchrony to result in a clearly localized or lateralized scalp ictal pattern. Conclusions: Sufficient source area and synchrony are mandatory cerebral EEG requirements for generating scalp‐recordable ictal EEG patterns. The dynamic interaction of cortical source area and synchrony at the onset and during a seizure is a primary reason for heterogeneous scalp ictal EEG patterns.