In addition to classic EEG and MEG analysis methods, which evaluate averaged signals, the analysis of single trials is becoming increasingly important. Short-term events, also known as transient events, form the basis for the well-known and frequently described continuous oscillations. However, a precise characterization of these events, which occur in the alpha band during visual stimulation, is still lacking. Such a characterization can help to better understand effects—such as entrainment and resonance effects—and to recognize and explain individual differences between people or patients.
In cooperation with the Center for Cognitive and Computational Neuroscience at the Complutense University of Madrid, the Biomagnetic Center, and the Werner Kaiser Research Center for MRI at Jena University Hospital, we conducted a combined E/MEG study with individualized intermittent photostimulation.
Transient events were detected in the time-frequency domain of the sensor space and characterized based on their number, frequency, and time or frequency width. Source configurations between individual trials and averaged trials were compared using the minimum norm estimation.
The signal-to-noise ratio of the averaged signals correlated strongly (r = 0.87) with the number of transient events detected. The number of events detected varied between modalities: a median of 76 events were detected in the EEG, 80 events in the magnetometers, and 89 events in the gradiometers. Twenty-five percent of the events overlapped between modalities. The temporal width of the bursts was approximately 250 ms, and the frequency width was 2 Hz. Topographic analysis in the sensor space showed increased activity above the occipital lobe. In the source space, all detected transient events were recorded in or near the occipital lobe. A median distance of 1 cm was found between the localizations in the single trial and those in the averaged signal.
Our results presented here expand the knowledge of transient events in single-trial EEG and MEG recordings during visual stimulation in the alpha band. The study thus provides a basis for future research in the areas of visual stimulation, single-trial source reconstruction, and modeling of resonance and entrainment effects.
Original publication: NeuroImage, Characterization of transient events during intermittent photic stimulation
from Hannes Oppermann, Ricardo Bruña, Daniel Güllmar, Carsten Klingner and Jens Haueisen
DOI: https://doi.org/10.1016/j.neuroimage.2025.121587
