P3-1-2. Assessment of the atypical cortico-cortical evoked potentials

Cortico-cortical evoked potential (CCEP) has been widely used to probe brain network. Typically CCEP waveform consists of two negative potentials, N1 (peak: 10–50 ms) and N2 (peak: 100–500 ms). We, however, occasionally encounter atypical responses, such as those with prolonged N1 peak latency. We attempt to classify these atypical patterns and clarify their anatomical distribution. We retrospectively reviewed CCEP responses in two patients with intractable focal epilepsy, in whom CCEPs were obtained bystimulating all the implanted subdural electrodes (IRB#443). We classified CCEP into 6 groups based upon the N1 and N2 peak latencies; IA: N1 (10–50 ms), N2 (100–500 ms), IB: N1 (10–50 ms), N2: (50–100 ms), IIA: N1 (50–100 ms), N2: (100–500 ms), IIB: N1 (50–100 ms) without definite N2, III: mirror CCEP response with positive peaks, IV: N1 (100–500 ms) without definite N2. Atypical CCEP responses (IIA, IIB, III, IV) accounted for 16.0% among all the recording. They mostly distributed in the temporal lobe. There was a tendency of preferred locations for each pattern; IIB in the lateral temporal region and frontal operculum, III in the superior temporal gyrus and mesial temporal region, IV in the temporal pole. Further case accumulation is warranted to verify the results, which helps understand the significance of CCEP for presurgical evaluation.