Single-trial EEG analysis reveals burst structure during photic driving

Oppermann, Hannes; Thelen, Antonia; Haueisen, Jens · 2023 · Crossref

DOI: 10.21203/rs.3.rs-2871389/v1

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Summary

This study challenges the conventional view that photic driving in the human visual cortex consists of continuous, ongoing oscillations. Instead, the authors argue that these responses are composed of transient, high-amplitude bursts of activity in single-trial electroencephalography (EEG) data. While standard analysis relies on averaging signals to improve signal-to-noise ratio, this approach obscures trial-to-trial variability. The research aims to determine if the continuous oscillations observed in averaged data during intermittent photic stimulation (IPS) are actually aggregates of brief, discrete bursts, thereby offering a new perspective on resonance and frequency entrainment phenomena. The researchers recorded 64-channel EEG data from fourteen healthy volunteers during visual stimulation with light flashes at eight frequencies ranging from 7.8 Hz to 23 Hz. The experimental design included constant stimulation periods and linear ramps, with participants keeping their eyes closed. Data were pre-processed using bandpass filtering and artifact removal, focusing on an occipital channel subset. Time-frequency representations were calculated using complex Morlet wavelets for both averaged and unaveraged single-trial data. A semi-automatic algorithm, refined by visual inspection, detected burst events based on power thresholds relative to pre-stimulation baselines. The analysis compared burst characteristics—number, central frequency, timing, and power—between resting states and stimulation periods, including second harmonics. The results revealed a distinct discrepancy between averaged and unaveraged data. Averaged signals showed continuous oscillations with frequency shifts toward the stimulation frequency and amplitude changes indicative of resonance or suppression. In contrast, unaveraged single trials exhibited no continuous oscillations but rather discrete bursts. These bursts demonstrated significant frequency entrainment, shifting toward the stimulation frequency, and showed increased occurrence rates during stimulation for middle and high frequencies (12.8–23 Hz), though not for low frequencies close to the individual alpha peak. The temporal distribution of these bursts correlated strongly with the time course of the main frequency in averaged data. Additionally, burst power increased significantly for high-frequency stimulations, consistent with resonance phenomena. The findings suggest that continuous brain rhythms observed in averaged photic driving data are emergent properties of transient burst events. This burst-based model explains previously observed amplitude fluctuations in averaged signals and aligns with recent literature questioning the continuity of other brain rhythms, such as beta and gamma bands. By revealing the underlying burst structure, this approach provides a more granular understanding of cortical synchronization mechanisms. The authors conclude that single-trial analysis could enhance basic neuroscience research and improve clinical applications of photic driving in diagnosing conditions such as epilepsy, autism spectrum disorders, schizophrenia, and migraine.

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