Rare Prosopometamorphopsia Case at Dartmouth College Distorts Faces into Demons

A rare distortion of face perception

To the human brain, other people’s faces carry exceptional importance. Vast amounts of neurological processing are dedicated to swiftly reading facial features, sorting them into familiar individuals or strangers who may pose a threat.

A 58-year-old man in the US, who attended Dartmouth College’s Department of Psychological and Brain Sciences, experiences faces rather differently. In his mind, the neural machinery responsible for recognising faces reshapes them into something monstrous - even demonic.

He was diagnosed with the rare neurological disorder prosopometamorphopsia, or PMO. His case has given researchers an unusual chance to explore how the visual system normally interprets identifying features to distinguish friend from foe.

For more than two and a half years before visiting the Dartmouth laboratory, he had seen the faces around him transform into grotesque caricatures. Lines and grooves formed across foreheads, cheeks and chins, while eyes and mouths became elongated.

Although the experience was initially upsetting, he gradually became accustomed to the strange masks his brain seemed to place over people he met. He remained able to recognise individuals, and his sense of reality stayed securely intact. However terrifying the appearances were, he knew he was not actually seeing demons.

Still, he knew that something was wrong. His life had not always been like this. He wondered whether his bipolar disorder or PTSD might be connected. It was also possible that the serious head injury he sustained in his early 40s had caused lasting harm, or that a toxic dose of carbon monoxide inhaled four months before the distortions began had contributed.

Dartmouth researchers investigate prosopometamorphopsia

When Dartmouth College psychologists Antônio Mello, Daniel Stehr, Krzysztof Bujarski and Brad Duchaine carried out a series of assessments, they found that their participant’s PMO did not manifest in a wholly typical way.

The disorder can take numerous forms: faces may appear demonic or dragon-like, jowls and cheeks can seem swollen, noses may look pinched, and eyes may appear enlarged. Normally, however, it affects pictures of faces just as much as it affects faces seen in person.

"In other studies of the condition, patients with PMO are unable to assess how accurately a visualization of their distortions represents what they see because the visualization itself also depicts a face, so the patients will perceive distortions on it too," says Mello, the case study’s lead author.

In this instance, the distortions occurred only with real faces. Photographs showing the same facial features appeared normal, giving the scientists a rare opportunity to chart the precise changes in appearance. They showed the man photographs of volunteers in the room, allowing detailed comparisons between the altered real-life faces and the unaltered images.

PMO, face blindness and Alice in Wonderland syndrome

In the past, prosopometamorphopsia was considered a type of face blindness, known as prosopagnosia. Evidence now suggests that the conditions do not have to occur together, and that their underlying mechanisms overlap only partly.

PMO is instead now understood as a visual distortion. It is one of around 40 conditions classed as Alice in Wonderland syndrome, which commonly alters perception so that people or objects appear bigger or smaller than they really are.

Being able to separate conditions with comparable neurological origins, even when their symptoms look radically different, is essential to providing accurate prognoses and treatments.

"We've heard from multiple people with PMO that they have been diagnosed by psychiatrists as having schizophrenia and put on anti-psychotics, when their condition is a problem with the visual system," says Duchaine, a psychologist at Dartmouth College and the case study’s senior author.

Researchers speculate that, in this participant’s case, a small 1-centimetre lesion above and to the left of his hippocampus, identified in an MRO scan, could be responsible.

After a year of monitoring, the lesion has not changed, which is encouraging. By discussing his experience, the man may also help others facing similar symptoms to feel less isolated and distressed.

"It's not uncommon for people who have PMO to not tell others about their problem with face perception because they fear others will think the distortions are a sign of a psychiatric disorder," says Duchaine.

"It's a problem that people often don't understand."

The case study was published in The Lancet.