Abstracts

Rationale: With use of EEG and MEG source imaging programs, Wennberg et al. (Clin Neurophysiol 2020;131:2915-25) localized generators of BETS to hippocampus, and modeled their electromagnetic signal by 2 rotating dipoles. My objective is to design EEG display-analysis that can help localize equivalent current dipole (ECD) and visualize its movement. It takes advantage of active reference, and employs polygraphic channel overlay (PGCO) for demonstrating latency differences among EEG peaks (Matsuo 2016, 2017: AES Annual Meeting Abstract). Systematic replacement of common reference can determine head-surface electrode pair registering maximal voltage values of opposite signs. Voltage difference thereof is ECD magnitude and is reference-free.

Methods: Mastoid and zygomatic pairs (T11/12 and F11/12, respectively) were added to 19 10-20 System electrodes. EEG was digitized at 200/s (EasyEEG 2), and reformatted off-line (Insight II). Standard EEG of 21-min duration was first screened in serial bipolar derivations (Figure A), and yielded 42 BETS. BETS were then examined in common reference derivations for phase relationship and inter-peak latency difference to select single illustrative example.

Results: 42 BETS had mean magnitude of 39 uv (SD: 9.6), and negative peaks were prominent over front-temporal derivations (Figure A). Peak movement was regularly seen, but inter-peak latency varied. Peaks were often ill-defined posteriorly. Relative background attenuation helped delineate phase relationship in detail (Figure B). Negative peak F8 and positive peak T11 revealed true phase reversal, and had ECD magnitude of 53 uv. Latency between negative peaks (initial 5 ms of [FP2-F4 overlay]) and [P4-O2] is 40 ms. Negative peak F8 comes 5 ms after [FP2-F4], and in turn, T12 follows F8 by 20 ms. Peak T8 begins rising before T12, and reaches peak 5 ms early. Downward slope of peak P8 lags behind peak T12. Peak latency between T12 and [P4-O2] is 15 ms. 2 true phase reversals were marked between negative peak F8 against positive peaks [O1-P7-T11], and negative peak T12 against positive peak F3. Negative peak [P4-O2] follows positive peaks [FP2-F4] and [Fz-FP1-F7], and does not form phase reversal. This phase relationship was not always seen among 42 BETS. It can be hypothesized In view of prominence of negative peak [FP2-F4] and lack thereof in [Fz-FP1-F7] that 2 anatomically discrete generator-surfaces, rotated at end of BETS propagation, contributed overlapping electrical fields. Positive peak moves posterior-to-anterior, while negative peak, anterior-to-posterior.

Conclusions: Standard EEG was reformatted for polygraphic demonstration of proposed BETS model involving deeply-placed, curved generator with anterior-posterior extension. This stand-alone method is suitable for broader application to initial examination of individual BETS within and across subjects, and needed further investigations over possible overlap between BETS and some pathological entities. Common reference AV10, averaging temporal plane electrodes, FP1/2, F7/8, T7/8, P7/8, and O1/2, was employed to minimize signal sampling bias secondary to asymmetry of northern- and southern-hemisphere electrode placements.

Funding: Please list any funding that was received in support of this abstract.: None.