Scalp EEG Fields Generated by Mesial Temporal Structures
Abstract number :
3.180
Submission category :
Year :
2001
Submission ID :
2950
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
F. Brunnhuber, MD, Clinical Neurophysiology, The Royal London Hospital, London, United Kingdom; D. Nayak, MD, Clinical Neurophysiology, King[ssquote]s College Hospital, London, United Kingdom; A. Valentin, MD, Clinical Neurophysiology, King[ssquote]s Coll
RATIONALE: To investigate factors determining whether epileptiform discharges of mesial temporal origin are detectable in the EEG.
METHODS: Foramen ovale (FO) electrodes were used as the only method of intracranial recording avoiding disruption of the skull and coverings. Sixty-eight epileptiform discharge (ED)patterns were obtained by averaging 3482 discharges from 13 presurgical patients. Discharges were classified as: scalp ED (SED) visible in raw EEG, spikes before averaging (SBA) visible with reference to FO, spikes after averaging (SAA)invisible in unaveraged, EEG, no scalp spike (NSS).
RESULTS: SEDs were seen in 21% of patterns, but a further 67% of FO spikes were visible on the scalp after averaging. 57% of SED were maximal at T1/T2, but only 39% of SBA and SAA, which had more diffuse scalp fields. Positive FO spikes were negative on the scalp and 86% were ipsilateral. Only 61% of negative FO spikes appeared ipsilaterally on the scalp, but 39% contralaterally.
CONCLUSIONS: Large anterior temporal EEG spikes (SED) arise by propagation to lateral neocortex, but smaller SBA and SAA are volume conducted. Spikes have greater lateralizing value if they are of positive polarity at the FO electrodes. Generators of positive and negative polarities at FO electrodes are differently orientated.
Support: The Fund for Epilepsy.