Researchers at Cedars-Sinai and the California Institute of Technology found some brain cells that specialize in recognizing emotions often make judgments based on preconceptions the viewer has rather than the feeling expressed by the other person.
To make their findings the researchers used electrodes placed deep within patients' brains (originally for other medical purposes) to record the electrical activity of the amygdala neurons. The team determined these neurons were "emotion-selective" because they responded differently to happy or fearful faces.
The patients were shown pictures of faces whose emotion was tricky to recognize because only certain features were revealed. Some neurons were more active at the site of happy faces while others responded more strongly to fearful ones.
"In these instances, the patients correctly judged the expressed emotion," said Ueli Rutishauser, PhD, assistant professor of neurosurgery and director of human neurophysiology research at Cedars-Sinai, senior author of an article published online the week of June 30 in the Early Edition of Proceedings of the National Academy of Sciences.
The team observed this also occurred when the neurons made and incorrect judgment about the face in question.
"When a fear face was incorrectly judged as happy, the neurons responded as if a happy face was correctly judged as happy -- in a sense, "correctly" representing the patient's incorrect judgment. When a happy face was incorrectly judged as a fear face, the neurons responded as if a fear face had been correctly judged as fear -- again, reinforcing the 'correctness' of the incorrect decision. This tells us that the neurons' responses were based on the subjective, perceived judgments that the patients made rather than on the 'ground truth' of the emotion shown in the stimulus," Rutishauser said.
When the team looked at neurons in the hippocampus (which also is involved with thoughts and emotions) they found the cells responded to visual stimuli, but those reactions were not related to the patients' subjective opinion.
Abnormal functioning in the amygdala is related to several disorders, such as autism and post traumatic stress disorder. This study could help researchers gain insight into what causes unprovoked fear or paranoia.
"To our knowledge, these findings are novel, in that they show that the response of emotion-sensitive neurons in the amygdala is biased toward the person's subjective judgment of emotions instead of simply responding to the actual features of the stimulus," said Shuo Wang, PhD, a postdoctoral scholar at Caltech and first author of the article.
