Purpose: Single pulse electrical stimulation (SPES) assists delineating epileptogenic tissue during long-term intracranial monitoring for pre-surgical evaluation. The SPES protocol consists of systematic stimulation of neighboring electrode pairs and analysis of responses in all other electrodes. SPES evokes early (ER) and delayed (DR) responses. DRs occur in epileptogenic tissue, but are stochastic: 10 stimuli are needed to reliably establish a response. ERs occur in healthy and diseased tissue and require only a single stimulus. We studied the spatial relation between ERs and DRs. If it is possible to predict DRs from ERs, this might improve the efficiency of SPES.
Method: Data of one patient with TLE recorded in 84 grid electrodes were used. We counted per electrode the number of stimulus pairs that evoked ERs (eER) and per stimulus pair the number of ERs that were evoked (sER). Similarly, for DRs, eDR and sDR were determined. Also, per electrode we counted the number of stimulus pairs that evoked both ERs and DRs, eERDR and vice versa for sERDR. We selected electrodes with eER or sER >median as eER50 or sER50. We tested whether values for eDR and sDR were significantly more in the eER50 and sER50 groups. Finally we tested whether the ratios eERDR/eDR and sERDR/sDR differed significantly from 0.5.
Results: eER values ranged from 0 to 41, median=8; sER:3-27, median= 17; eDR:0-28, median=17 and sDR:0-26,median=9. eDR and sDR values were higher in eER50 (p < 0.001) and sER50 (p = 0.1) electrodes. The ratios of eERDR/eDR and sERDR/sDR ranged from 0 to 1, median=0.24 and 0–0.64, median=0.25 respectively, with the average significantly lower than 0.5 (p < 0.001).
Conclusion: The correlation between eER50 electrodes and high values of eDR indicates that ERs and DRs seem to occur within the same network. The low ratio eERDR/eDR suggests that ERs and DRs are not directly related. We will analyze more patients to confirm these findings.
|Publisher||Wiley Periodicals, Inc|
|Number||Supplement S1: Special Issue|
|Conference||31st International Epilepsy Congress Istanbul, Turkey 5th-9th September, 2015, Istanbul, Turkey|
|Period||5/09/15 → …|
- Evoked Potential
- Single Pulse Electrical Stimulation