The man who saw twisted mouths

Imagine you lived in a world where the faces of everyone you met had a "deformed" mouth. One man actually began experiencing this disturbing vision rather suddenly. This incredible clinical case was reported by ophthalmologists in eNeurologicalSci, a review published by the World Federation of Neurology. So what exactly was the patient suffering from?

The 62-year-old man visits his doctor with an unusual complaint: faces look deformed to him. More specifically, while the nose and eyes appear normal, another part of the face always looks twisted and enlarged: the mouth. He isn’t suffering from prosopagnosia (an inability to identify faces) and he can correctly identify landscapes. Indeed, everything appears normal to him, except people’s mouths! Nevertheless, he admits having difficulty reading letters and numbers on his computer screen; but no trouble writing. Moreover, he has never suffered from any type of ophthalmological disease. His visual acuity is normal.

In order to understand the cause of these mouth distortions, the doctors have the patient undergo an MRI. The scan reveals a lesion in the corpus callosum. This structure (which consists of a very large number of fibers and white matter) forms a kind of “bridge” between the two hemispheres, allowing them to communicate. The lesion is located in the left splenium of the corpus callosum (at the back). This is exactly where visual information passes between the two hemispheres.

With this knowledge, the doctors were able to determine the cause of the disorder. In this patient, the transmission of information related to facial recognition was interrupted as it passes from the left portion of the occipital visual cortex (via the splenium of the corpus callosum) to the right part, in the fusiform gyrus (the “face area”). The disorder has a name: Prosopometamorphopsia, or a distortion in face perception that causes them to look deformed, flattened, or enlarged. And this distortion can apply to the entire face or just a single element. The disorder is also responsible for the patient’s difficulties with reading letters and numbers on his computer.

Joachim Bodamer, a German psychiatrist, reported the first case of prosopometamorphopsia in 1947. One of his patients claimed faces looked "like Dali's soft watches!"
Source: McCarty CW, Gordon GM, Walker A, Delioc P, Kolarczyk RA, Pieramici DJ, “Prosopometamorphopsia and alexia following left splenial corpus callosum infarction: Case report and literature review”, in eNeurologicalSci, March 2017.

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