The brains of patients with the skin condition psoriasis are less responsive to expressions of disgust on other people's faces, a neurological device that may help them cope with the social stigma of the disease, a new study has found.
Men with psoriasis, a condition where skin lesions and scaly patches are often visible on the surface of the skin, had a weaker than normal response in the insular cortex when shown images of disgusted faces, according to an online report in the Journal of Investigative Dermatology.
The insular cortex is the region of the brain associated with the feelings and observation of disgust.
"We hypothesize that patients with psoriasis, in this case male patients, develop a coping mechanism to protect them from stressful emotional responses by blocking the processing of disgusted facial expressions," Dr. Christopher E. M. Griffiths of England's University of Manchester and colleagues wrote.
Psoriasis is a chronic autoimmune disease that affects as many as 7.5 million people in the United States, according to the National Institutes of Health. The disease occurs when the immune system signals cause the growth cycle of skin cells to speed up, which often results in red patches or lesions covered with a silvery white buildup of dead cells.
In earlier research, Griffiths and colleagues found that psoriasis patients commonly believe they will be judged by their skin and therefore anticipate and avoid these situations. They theorized that recognition of disgust in the expressions of others is a key cue for psoriasis patients.
In their new study, the researchers sought to determine if the social impact of psoriasis was associated with altered cognitive processing of the expression of disgust.
They had 13 right-handed male patients with psoriasis and 13 age-matched male controls look at images of human faces with neutral expressions and disgusted expressions.
As the subjects looked at the photographs, the researchers imaged their brains for blood oxygenation level-dependent (BOLD) responses using functional magnetic resonance imaging (fMRI) to measure neuronal activity.
Feelings of disgust and observation of disgust are known to activate neurons in the insula cortex. The researchers also had the participants perform a facial expression recognition task (FERT), during which they were shown images and asked to identify various levels of disgust.
The fMRI imaging showed significantly less BOLD response in the bilateral insula of psoriasis patients compared than the control subjects.
This result was corroborated by the FERT portion of the study, which indicated that psoriasis patients were just as able as controls to identify expressions of fear or sadness, but less able to identify all intensities of disgust in the images they were shown.
In addition to proposing that this might be a coping mechanism to avoid stress, the researchers noted that the observation of pain in others is mediated by the insula and that these responses are attributed to empathy.
"It is therefore possible that the reduced insula response in psoriasis patients is associated with reduced empathy for disgust, perhaps resulting from desensitization," they wrote. However, they noted that they found no abnormal responses in other areas of the brain that are involved in empathy.