Abstracts

RATIONALE: Extraoperative cortical localizing stimulation (LS) is a standard clinical tool used to assess brain function prior to epilepsy surgery. We previously have shown that brief pulses of electrical stimulation (BPS) can terminate afterdischarges (ADs), and that wavelet-crosscorrelation analysis could predict the conditions under which BPS would be most likely to terminate ADs. The objective of this study was to investigate the site(s) of initiation and the direction(s) of propagation of epileptiform discharges using wavelet-crosscorrelation and time lag analyses. METHODS: We assessed all ADs that occurred in response to LS in seven patients, by measuring wavelet-crosscorrelation coefficients (WCC) and time lag (TL) between electrode pairs. We compared WCC and TL in epoch 1 (baseline) which was prior to LS, in epoch 2 which was after LS but before BPS, and in epoch 3 which was after BPS. We assessed using ANOVA (p < 0.01). RESULTS: There were significant differences at many electrode pairs in WCC results between epochs 1 and 2 and 2 and 3 in all patients. On the other hand, there were few significant differences in WCC between epochs 1 and 3. We also compared TL values among epochs. TL analysis indicated that similar activity would often occur at pairs of electrodes but with activity propagating between sites, rather than occurring simultaneously. The directions and the values of the time lag in epoch 2 tended to be different from those in epoch 1 and 3. Brain activity returned to baseline after successful BPS at most pairs of sites. CONCLUSIONS: WCC TL mapping can help investigate the changes in cortical activity that occur after BPS. ACKNOWLEDGMENTS: This work was supported in part by Research for the Future Program of Japan Society for the Promotion of Science (JSPS) under the Project "Integrated Network Architecture for Advanced Multimedia Application System" (JSPS-RFTF97R16301), Epilepsy Research Foundation and Sumitomo Life Insurance Welfare Services Foundation.