Midfrontal theta oscillations in defensive responses to threats of varying imminence: An EEG study

Abstract

This project focused on midfrontal theta power (4-8 Hz), which is believed to mainly originate in the dorsal anterior cingulate cortex. We specifically examined midfrontal theta in the context of varying threat imminence. Namely, more theta power has been associated with fear expression, but several studies failed to replicate such an association. Additionally, midfrontal theta may reflect threat appraisal processes, leaving the exact role of midfrontal theta power in threat processing unknown. While the threat imminence continuum provides a framework for better experimental separation of threat appraisal and fear expression by including distal and imminent threats, respectively, no study has used such a paradigm in investigating theta power. We therefore developed a new experiment in which varying threat imminence is combined with different threat probabilities. In addition to midfrontal theta power, we further explored delta power (0.5-4 Hz) as a potential indicator of threat appraisal within this paradigm. We recorded the EEG of thirty participants, alongside startle electromyography (EMG), and collected ratings of stimulus aversiveness and shock expectancy. While participants correctly internalized the threat probability linked to different stimuli, startle EMG did not effectively differentiate varying levels of threat. Threat also did not elicit a stronger burst of theta power regardless of probability or the imminence phase. Surprisingly, the greatest burst of theta power occurred during safe trials, even before the onset of the actual stimulus indicating safety. An increase in delta power was observed during a distal threat. Although the findings may be affected by methodological issues, they do not support midfrontal theta or delta power serving as reliable markers of threat appraisal or fear expression. This project adds to the growing exploration of oscillatory activity in response to threat and emphasizes the need for additional research to uncover the relationship between oscillations and distinct aspects of threat processing.