Abstracts

RATIONALE: The authors previously have reported that brief pulse stimulation (BPS) can terminate the afterdischarges (ADs) caused by localizing stimulation (LS) during extraoperative functional mapping (Lesser et al., Neurology 1999; 53:2073-2081). In this study, we analyzed the synchronization status of cortex manifesting ADs and not manifesting ADs, to determine under which conditions BPS can suppress ADs.
METHODS: Electrical cortical stimulation was performed in six patients undergoing presurgical evaluations using subdural electrodes. We evaluated the conditions altering BPS efficacy in 194 electrodes showing, and not showing ADs. We investigated inter-electrode synchronization for consecutive 2-second time periods before LS, and between LS and BPS, in extended frequency ranges between 2 and 100 Hz, using a new measure called [dsquote]neighbor correlation count[dsquote] (NCC) based on wavelet theory. NCC analyzes the individual correlation between an electrode and its surrounding electrodes to evaluate the synchronization status of the ADs. For each electrode, we measured wavelet correlations amplitude (WC-amp), absolute time lag (WC-atl), and the fraction of channel pairs that exceed a predetermined threshold of 90% of maximum WC-amp (%-NCC). Alternating logistic regression (ALR) and generalized linear model (GLM) were used for statistical analysis.
RESULTS: In the 4-8 Hz frequency band, assessment of periods 0-2 and 2-4 seconds before BPS showed that BPS efficacy improved with increases in WC-amp (odds ratios 73.2 and 18.2, respectively, p=0.060 and 0.073). BPS could stop ADs 14.9 and 12.6 seconds faster per unit WC-amp increase during the same period (p[lt]0.001). In the 8-16 Hz band, assessment of the 2-4 and 4-6 seconds before BPS also showed that BPS efficacy improved with increases in WC-amp (odds ratios 12.6 and 34.9 respectively, p=0.067, 0.022). BPS could stop ADs 15.6 and 9.7 seconds faster per unit WC-amp increase during this time (p=0.049 and p[lt]0.001, respectively). In the 4-8 Hz band, BPS efficacy improved by 8-11% per unit %-NCC increase over the period 0-8 seconds before LS (p[lt]0.001 to p=0.013).
CONCLUSIONS: BPS was more effective when WC-amp and %-NCC values were higher in the 4-8 and 8-16 Hz bands, in other words when ADs were more synchronized in these frequency bands. NCC analysis may help predict conditions during which BPS is more likely to be effective. NCC analysis also may help elucidate mechanisms underlying seizure generation, spontaneous termination, and external blocking.
[Supported by: Postdoctoral fellowship from Korean Science and Engineering Foundation (KOSEF).]