In the experiment, participants gave their first impressions of neutral faces immediately after seeing emotional faces, including some that were smiling (prompting positive emotions) and some that were fearful (prompting negative emotions).
Using Transcranial Magnetic Stimulation (TMS), a technique that produces a magnetic field that can temporarily “knock out” or inhibit activity in specific parts of the brain, the researchers discovered that when the lateral prefrontal area of the brain (a region known for executive function) was inhibited by the stimulation, participants showed more emotional spillover.
TMS therapy is approved by the FDA for treatment of depression, and this study may shed light on why stimulating parts of the prefrontal cortex is successful in improving the ability to regulate negative emotions.
“It was interesting because participants saw the emotional faces very briefly,” said Dr. Regina Lapate, Center for Healthy Minds collaborator and current postdoctoral researcher at the University of California, Berkeley, who led the work.
“And when asked afterward, they didn’t think that they had been influenced by it in their ratings. Having their prefrontal cortex disrupted generated spillover onto their unrelated events that followed. Emotional spillover can happen without us being aware of it.”
The findings show that when the lateral prefrontal cortex was intact (when the brain was not inhibited by TMS), the person did not show spillover when looking at subsequent neutral faces. And when the opposite occurred — when the lateral prefrontal cortex was inhibited by TMS — emotional spillover occurred more frequently and with greater intensity.
Three days later outside of the laboratory, participants still showed that emotional bias when asked to rate the same neutral faces, suggesting that the negative emotional spillover they first showed in the laboratory produced long-lasting, biased first impressions.
“If your first impression of someone is formed when you’re experiencing emotional spillover from a previous context, that negative impression may stick,” Lapate adds.
Research shows that mindfulness meditation can improve emotion regulation and connectivity between the prefrontal cortex and emotion-centered areas of the brain such as the amygdala. If researchers know that there’s a cause-and-effect relationship between these areas of the brain, they can more accurately develop treatments to target these areas and improve well-being.
“We are excited about this experiment because it demonstrates the causal role of the prefrontal cortex in regulating emotional behavior,” said Dr. Richard Davidson, William and James Vilas Professor of Psychology and Psychiatry who worked on the study and directs the Center for Healthy Minds. “It invites the possibility that strategies that promote prefrontal engagement may have beneficial consequences for emotion regulation.”
The next step is to test whether the reverse works; for example, can TMS stimulation that increases neural firing in the prefrontal cortex lead to a decrease in negative emotional spillover? The research team will also investigate how the lateral prefrontal cortex as a whole changes the neural coding for positive and negative information.
The findings are published in the journal Psychological Science.
Source: Association for Psychological Science