The neural footprint of disgust is evident in sensory and moral experiences

Disgust is one of the six basic human emotions, along with happiness, sadness, fear, anger and surprise. Disgust typically occurs when a person perceives a sensory stimulus or situation as disgusting, unpleasant, or otherwise aversive.

Past psychological research has defined disgust as an avoidant-defensive emotion, linking it to certain facial expressions, movements and physiological reactions. Although disgust is primarily associated with unpleasant tasting foods, unpleasant odors, or the sight of disgusting images, it can also occur in response to other stimuli, including unpleasant social interactions.

Researchers from the University of Electronic Science and Technology of China and other institutions recently conducted a study aimed at better understanding the neural underpinnings of disgust and its generalization to contexts beyond food intake. Their findings, published in Nature Human Behaviorsuggest that the neurofunctional signature of subjective disgust is the same for oral disgust and unpleasant socio-moral experiences.

“Although disgust has its origins in the hard-wired mammalian disgust response, the conscious experience of disgust in humans is highly dependent on subjective evaluation and may even extend to socio-moral contexts,” write Xianyang Gang, Feng Zhou and their colleagues in their paper.

“In a series of studies, we combined functional magnetic resonance imaging (fMRI) with predictive machine learning modeling to create a comprehensive neurobiological model of subjective disgust.”

Subjective disgust is associated with and predicted by distributed brain regions. A, VIDS threshold map. B, Threshold transformed 'activation' map of VIDS. C, Combination of VIDS and transformed 'activation' map. Images are thresholded at q < 0.05, FDR adjusted. Hot colors indicate positive weights (a) or associations (b), cool colors indicate negative weights (a) or associations (b). Source: Nature Human Behavior (2024). DOI: 10.1038/s41562-024-01868-x

Participants were shown various images designed to evoke feelings of disgust and were asked to respond naturally to the images. After viewing each image, participants were asked to rate their level of disgust on a scale from 1 (little/no disgust) to 5 (high disgust).

By observing participants' brain activity using fMRI and analyzing the collected data using a machine learning model, the researchers were able to delineate the neural signature associated with subjective perceptions of disgust. This signature accurately predicted self-reported feelings of disgust in study participants, generalizing well to basic disgust, taste disgust, and socio-moral reactions to unfair offers in the game.

"The experience of disgust was encoded in distributed cortical and subcortical systems and demonstrated distinctive and shared neural representations with subjective fear or negative affect in the interoceptive-emotional awareness and conscious appraisal systems, while the signatures most accurately predicted the corresponding target experience," they write. Gan, Zhou and their colleagues in their article.

"We provide an accurate functional magnetic resonance imaging signature of disgust with high potential for resolving current evolutionary debates."

A recent study by Gan, Zhou and their co-authors describes a pattern of activity throughout the brain associated with the subjective experience of disgust. In particular, subjective disgust was simultaneously encoded in different brain regions rather than in separate regions.

Interestingly, the researchers observed the same neural signature throughout the brain in a variety of situations where people experience disgust, from tasting unpleasant food to empathizing with others in pain or receiving an unfair offer. These results may soon pave the way for further neuroscientific research focusing on the neurofunctional signature of disgust, potentially leading to exciting new discoveries.