Strong health messages increase audience brain coupling.

Mass media messaging is central for health communication. The success of these efforts, however, depends on whether health messages resonate with their target audiences. Here, we used electroencephalography (EEG) to capture brain responses of young adults - an important target group for alcohol prevention - while they viewed real-life video messages of varying perceived message effectiveness about risky alcohol use. We found that strong messages, which were rated to be more effective, prompted enhanced inter-subject correlation (ISC). In further analyses, we linked ISC to subsequent drinking behavior change and used time-resolved EEG-ISC to model functional neuroimaging data (fMRI) of an independent audience. The EEG measure was not only related to sensory-perceptual brain regions, but also to regions previously related to successful messaging, i.e., cortical midline regions and the insula. The findings suggest EEG-ISC as a marker for audience engagement and effectiveness of naturalistic health messages, which could quantify the impact of mass communication within the brains of small target audiences.