Functional Connectivity of the Epileptogenic Zone Revealed by Spike- Averaging
Abstract number :
B.08
Submission category :
Year :
2001
Submission ID :
410
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
L. Ampaw, B.A., Neurology, Johns Hopkins University, Baltimore, MD; J.P. Sepkuty, M.D., Neurology, Johns Hopkins University & Hospital, Baltimore, MD; L. Hao, Ph.D., Neurology, Johns Hopkins University, Baltimore, MD; R. Webber, Ph.D., Neurology, Johns Ho
RATIONALE: Seizures may disrupt cortical function not only in the epileptogenic zone, but also through the spread of abnormal electrical discharges outside of the epileptogenic zone. This spread may also extend the boundary of the epileptogenic zone. If the functional connectivity of two regions is particularly high (e.g. due to dense cortical-cortical white matter projections or reduced synaptic thresholds), neuronal discharges in one may evoke synaptic activity in the other. By a similar mechanism interictal spikes could evoke potentials in distant cortical regions. Spike-triggered averaging could improve the signal-to-noise ratio of these potentials. We first reported spike-evoked potentials in a patient with a right temporal-occipital seizure focus (American Clinical Neurophysiology Society, 1999). In this study, we present two more patients with similar findings.
METHODS: We analyzed the electrocorticogram (ECoG) of two patients with subdural electrodes implanted for epilepsy surgery. Neither patient had a lesion on MRI. In patient [pound]1, spikes in left anterior temporal regions were used as the trigger for ECoG signal averaging. In patient [pound]2 spikes in right occipital regions were used as the trigger for ECoG signal averaging. In each patient 80-120 interictal spikes of the same morphology, appearing in the same channel, were manually selected and marked. The averages of two subsets of spikes were superimposed to verify their reproducibility. The raw ECoG was also visually examined for the presence of the potentials seen after averaging.
RESULTS: After averaging 88 left anterior temporal spikes in patient [pound]1, a 100-200 microvolt potential was found in electrodes overlying left posterior temporal and occipital regions with a latency of 200 ms. After averaging 100 right occipital spikes in patient [pound]2, a 100-150 microvolt potential was found in three electrodes overlying the right inferior lateral temporal region with a latency of 200 ms. These potentials were not present upon visual inspection of the raw ECoG.
CONCLUSIONS: This study provides further evidence for a novel type of evoked potential generated by epileptic spikes. The data emphasizes the strong functional connectivity between the temporal and occipital lobes in the patients we studied. This technique may be used to investigate the human epileptogenic zone, as well as its functional connectivity with outlying cortical regions.