A rare disease appears to protect the brain from schizophrenia.

 

In 1950, two researchers discovered something puzzling.

Writer Hector Sevigny, who lost his sight as an adult, and psychologist Sidel Braverman discovered an interesting pattern while studying the psychological state of the visually impaired. They found that schizophrenia, a serious mental illness present in almost every society, did not appear at all in individuals born blind.

These observations went largely unnoticed for decades due to a lack of understanding of the disease and insufficient patient data. Then, in the early 2000s, large-scale national health databases enabled researchers to track the entire population from birth to adulthood, and the patterns of schizophrenia were confirmed once again.

The most definitive evidence came from a 2018 whole-population study that tracked approximately 500,000 children born in Western Australia between 1980 and 2001. While 1,870 of these children developed schizophrenia, not a single one of the 66 children born blind developed the disease.

** Although this sample of visually impaired children is small, a synthesis of evidence accumulated over more than 70 years reveals a consistent trend. In other words, not a single case of schizophrenia has ever been reported among individuals with congenital visual impairment. This protective effect appears to be specific only to cortical visual impairments caused by damage to the brain's visual cortex.

People who lose their sight in adulthood or lose it due to eye damage rather than brain damage can still develop schizophrenia. This clearly demonstrates that visual impairment itself is not the decisive factor.

Specific characteristics of the visual brain play a decisive role.

This may sound strange. This is because schizophrenia is commonly associated with auditory hallucinations or abnormal beliefs, but is generally considered unrelated to vision. However, the answer lies not in what people see, but in how the brain utilizes vision to understand the world.

Scientists now understand schizophrenia, at least in part, as a disorder of prediction.

The brain constantly generates expectations about the surrounding environment and contrasts them with signals from sensory organs. In schizophrenia, this process appears to be disrupted.

Excessive weight is given to weak or random signals, coincidences feel meaningful, and thoughts may feel as if they are coming from outside oneself.

The boundary between imagination and reality begins to blur.

Currently, most treatments target brain chemistry, particularly the dopamine system. While these drugs are helpful to many people, they are not effective for everyone and can be accompanied by serious side effects.

If schizophrenia is partly related to how the brain learns to predict and interpret reality, future treatments will need to focus on perception, learning, and how the brain evaluates uncertain information.

**The Problem of Prediction**

Vision plays a powerful role in shaping this system, particularly during infancy. The visual cortex is one of the largest and most connectivity-rich regions in the brain, involved not only in vision but also in learning, attention, and emotion. If visual stimulation is not received from birth, the brain develops differently.

Brain imaging studies show that in patients with congenital cortical blindness, this region is often reorganized to take charge of functions such as language, memory, and reasoning.

Some researchers believe that this early reorganization may provide a form of protection.

If visual input does not constantly generate ambiguous or unpredictable signals, the brain acquires a more stable way of interpreting the world, which can reduce the risk of false predictions characteristic of schizophrenia. Timeliness is very important.

Even in cases where eyesight is lost during childhood, losing it later does not appear to provide the same protective effect. This is because by that point, the brain has already been shaped by years of visual experiences.

These facts do not mean that blindness can be a practical preventive measure against schizophrenia. However, they may suggest a new way of thinking about schizophrenia and potentially new treatments.

Research is now looking at drugs that act on glutamate, a brain chemical involved in learning and communication between nerve cells.

Glutamate systems are particularly active in the visual cortex and in circuits that help the brain filter out what's important from what can be ignored. These aren't treatments based on blindness itself, but on what congenital blindness reveals about how a stable, well-organized brain develops.

The field is still at an early stage. But the hope is that by better understanding brain development from the very beginning, scientists might one day find ways to reduce the risk of schizophrenia or prevent its most severe forms from taking hold.

Nearly a century later, the curious observation that Chevigny and Braverman had accidentally made continues to shape how scientists think about one of the most complex and least understood medical conditions.

Ahmed Elbediwy, Senior Lecturer in Cancer Biology & Clinical Biochemistry, Kingston University and Nadine Wehida, Senior Lecturer in Genetics and Molecular Biology, Kingston University