Abstracts

Rationale: Interpretation of intraoperative electrocorticography (ioECoG) is limited by effects of anesthesia and interictal short recording. Resection of spikes by visual inspection in ioECoG did not entirely correlate with good seizure outcome. In previous study, analysis of phase-amplitude coupling (PAC) between fast ripples (FRs) and slow waves in the implanted subdural electrodes ECoG could localize the epileptogenic zone. We tested the hypothesis that the analysis of PAC in ioECoG could be the indicative of the epileptogenicity in drug-resistant mesial temporal lobe epilepsy (mTLE). Methods:  We retrospectively reviewed 8 patients with drug-resistant mTLE, who underwent selective amygdalohippocampectomy or anterior temporal lobectomy. IoECoG records at a sampling rate of 1000Hz for 10 minutes in hippocampus, amygdala and lateral temporal cortex. We calculated modulation index (MI), reflecting the degree of PAC, between 80-200Hz (ripples)/200-300Hz(FRs) and 3-4Hz, in the selected 5 epochs of 1-minute ioECoG data. We compared MIs in hippocampus and amygdala before resection between good seizure outcome group (n=6) and poor seizure outcome group (n=2). We compared MIs in lateral temporal cortex before and after the mesial epileptic focus resection between those two outcome groups. Results:  MI(Ripples/FRs&3-4Hz) in hippocampus of the good seizure outcome group [4.2±1.5/0.7±0.3] were significantly lower than those [8.5±1.5/1.4±0.3] of the poor seizure outcome group (p<0.01). MI(Ripples/FRs&3-4Hz) in amygdala of the good seizure outcome group [4.1±0.1/0.6±0.1] were significantly lower than those [8.7±0.3/2.0±0.1] of the poor seizure outcome group (p<0.01). In the good seizure outcome group, MI(Ripples&3-4Hz) in lateral temporal cortex were significantly decreased from 4.4±3.5 to 1.5±1.2 (p<0.01). MI(FRs&3-4Hz) in lateral temporal cortex were significantly decreased from 0.7±0.5 to 0.2±0.1 (p<0.01). In the poor seizure outcome group, MI(Ripples&3-4Hz) in lateral temporal cortex were significantly increased from 1.9±1.5 to 5.1±3.9 (p<0.01). MI(FRs&3-4Hz) in lateral temporal cortex were significantly increased from 0.3±0.1 to 0.5±0.3 (p<0.01). Conclusions: The decremental MI in lateral temporal cortex after the resection of mesial temporal structures may predict the postoperative good seizure outcome. PAC in ioECoG could be the biomarker of delineating the residual epileptogenic zone.  Funding: No funding