The brain has an intricate system to process visual information and give rise to vision. But even with a healthy visual system, one can still go blind.

This seems to be what happened to a woman in Germany, who lost her eyesight at one point in her life. Her doctors at the time thought the blindness was a result of brain damage she suffered in an accident. But years later, during psychotherapy treatment for her psychiatric disorder, she began to switch between blind and sighted states. Eventually, she almost entirely regained her ability to see.

"The regaining of vision happened immediately after a therapy session in which a major traumatic event had been worked on. That was many years after the blindness first began," said Dr. Hans Strasburger of Ludwig Maximilian University in Munich, who saw the patient once for an fMRI, and recently coauthored a report describing the case, published in PsyCh Journal.

A woman with 10 personalities

About 14 years ago, the then 33-year-old woman, here referred to by her initials, B.T., was diagnosed with dissociative identity disorder and visited Dr. Bruno Waldvogel for psychotherapy at his practice in Munich, Germany. Dissociative identity disorder, previously referred to as multiple personality disorder, is characterized by disturbances of memory and coexistence of at least two distinct personality states. The disorder is thought to result from extreme and repeated trauma in childhood, frequently involving severe emotional, physical or sexual abuse, according to Cleveland Clinic. However, it is a controversial diagnosis, with some psychiatrists questioning its validity and arguing that it is a culture-bound artifact, often driven by therapist suggestion.

B.T. came to see Waldvogel with her guide dog and told the therapist she had gone blind after suffering an accident 13 years earlier. Specifically, her vision first became severely impaired following the accident and then she gradually went completely blind. When Waldvogel looked at her medical records, he saw that she had been diagnosed with cortical blindness from trauma to her skull and brain.

Over the course of psychotherapy with Waldvogel, B.T.'s dissociative identity disorder manifested itself through the presentation of more than 10 personalities, which differed by name, voice, reported age, gender, gesture, attitudes, facial expressions, personal inclinations, aptitudes, temperament and other character traits. In some of the states, the woman could communicate only in English, in others only in German, and then there were those in which she spoke both languages. (The woman spent some time in an English-speaking country as a child, where she only spoke English.)

In her fourth year of psychotherapy, she suddenly recognized a few words on the title page of a magazine right after a psychotherapy session. At the time she was in one of her adolescent male identity states.

Although the woman became able to recognize whole words, she still could not recognize the letters that constituted those words. But in subsequent sessions, she began to recognize brightly lit objects and then eventually, everything else that was normally visible to others.

Initially her ability to see was limited to that one personality state. But as she continued the therapy, more and more of her personality states became sighted. In fact, her "sighted and blind states could alternate within seconds," the doctors wrote.

A wish not to see

The doctors' observations were later confirmed in an electrophysiological measurement used to detect vision impairment. The test showed that visual evoked responses —the brain's electrical activity in response to visual stimuli — were absent in the blind states but were normal and stable in the seeing states.

The brain is a flexible and plastic organ, and it is possible for it to reorganize itself after an injury. But this is "highly unlikely" to be the case for B.T., the researchers said, as evidenced by B.T.'s rapid switching between blind and sighted states. Instead, the researchers think that the previous injury to the woman's skull and brain and the ensuing temporary impairment of vision may have acted as a prime for her eventual loss of vision that was actually of psychogenic nature. In other words, B.T.'s visual brain could function and see, but sometimes it could be turned blind psychologically.

Waldvogel still sees B.T. from time to time for crisis intervention. Although B.T.'s newfound vision has extended to most of her personality states, two blind personality states still remain. "These presumably serve as a possibility for retreat," Strasburger told Braindecoder. "In situations that are particularly emotionally intense, the patient occasionally feels the wish to become blind, and thus not 'need to see.'"

Vision, on and off

It appears that the incoming visual information received by B.T.'s brain gets modulated depending on her personality state. But it's not clear where and how exactly in the brain this process may occur.

There are some theories, however. The brain processes visual information in a hierarchical manner, with each level dealing with an aspect of the processing and sending the results higher up. One possibility is that psychogenic blindness happens at the level of the lateral geniculate nucleus (LGN) — a relay center for vision in the thalamus, which, some researchers have suggested, may act as an early gatekeeper of visual awareness. Interestingly, this same brain area is suggested to have a role in another unsolved vision phenomenon called blindsight. People with this condition are physically blind due to damage to their primary visual processing areas in the brain, but can still see unconsciously and continue to be aware of the objects shown to them or even navigate their surroundings while avoiding running into obstacles.

Another potential mechanism for psychogenic blindness is that the incoming visual information is modulated by selective attention—that is, somehow, the attention system completely ignores the visual information sent to the brain. This has been previously linked to both cortical areas and the LGN.

A brain with multiple programs

B.T.'s case is not the only documented instance of psychogenic blindness. Earlier this year, for example, researchers described the case of a 21-year-old woman in Ethiopia, who suddenly became blind following stressful life events, but regained her vision with treatment. According to another report, a whole family went temporarily blind in the absence of any physical abnormality in their vision.

While the exact nature of psychogenic blindness remains to be determined, B.T.'s case adds some insights to the discussion of the controversy surrounding the diagnosis of dissociative identity disorder. Previous research based on psychobiological evidence from patients with the disorder has shown that different personality states are linked with differing cortical activation patterns, the researchers said. B.T.'s case shows that "differences between personality states are not limited to higher-level processing but can differ with respect to the fundamental processing of early sensory information and corresponding perceptual change," they said. "It therefore provides compelling evidence for the existence of the dissociated identities in a more biological sense."

The findings presented in the report by Strasburger and Waldvogel add to the research demonstrating that dissociative identity disorder "is a legitimate psychophysiologically based syndrome of psychological distress," said Dr. Richard P. Kluft, a clinical professor of psychiatry at Temple University School of Medicine, who disagrees with the notion of the condition as a cultural and therapeutic artifact. While culture may influence the way it is expressed in different places, it is essentially the same syndrome that occurs worldwide, as it "represents the mind's attempt to compartmentalize its pain," Kluft said.