Intracranial EEG substrates of scalp EEG interictal spikes.
OBJECTIVE
To determine the area of cortical generators of scalp EEG interictal spikes, such as those in the temporal lobe epilepsy.


METHODS
We recorded simultaneously 26 channels of scalp EEG with subtemporal supplementary electrodes and 46 to 98 channels of intracranial EEG in 16 surgery candidates with temporal lobe epilepsy. Cerebral discharges with and without scalp EEG correlates were identified, and the area of cortical sources was estimated from the number of electrode contacts demonstrating concurrent depolarization.


RESULTS
We reviewed approximately 600 interictal spikes recorded with intracranial EEG. Only a very few of these cortical spikes were associated with scalp recognizable potentials; 90% of cortical spikes with a source area of >10 cm(2) produced scalp EEG spikes, whereas only 10% of cortical spikes having <10 cm(2) of source area produced scalp potentials. Intracranial spikes with <6 cm(2) of area were never associated with scalp EEG spikes.


CONCLUSIONS
Cerebral sources of scalp EEG spikes are larger than commonly thought. Synchronous or at least temporally overlapping activation of 10-20 cm(2) of gyral cortex is common. The attenuating property of the skull may actually serve a useful role in filtering out all but the most significant interictal discharges that can recruit substantial surrounding cortex.
Tao
James X
JX
Department of Neurology, Adult Epilepsy Center, University of Chicago, Illinois 60637, USA. jtao@neurology.bsd.uchicago.edu
Ray
Amit
A
Hawes-Ebersole
Susan
S
Ebersole
John S
JS
D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods / Q000706:statistics & numerical data*; D004594:Electrophysiology; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D005625:Frontal Lobe / Q000503:physiopathology; D006801:Humans; D021621:Imaging, Three-Dimensional; D008991:Monitoring, Physiologic / Q000379:methods; D011300:Preoperative Care; D012535:Scalp; D013702:Temporal Lobe / Q000503:physiopathology