On a spring day in 1938, a 25-year-old man was left lying on the ground. A projectile had crossed his head on the Valencian front of the Spanish Civil War. When he recovered consciousness two weeks later, the Republican soldier had experienced a shocking change: under certain conditions, he saw the world backwards. The 28-year-old doctor Justo Gonzalo attended the patient in a nearby military hospital. The projectile, probably shot by the Francoists, had partially destroyed the ridges on his cerebral cortex in the left parieto-occipital region. The wounded man, however, survived miraculously, without needing operations or special care. Gonzalo, born in Barcelona in 1910, realized that the unique case — who he called Patient M — could illuminate the functioning of the human brain.

The doctor and M survived the war and continued seeing each other for almost half a century, until Justo Gonzalo’s death in 1986. The researcher’s daughter Isabel Gonzalo has dusted off her father’s archives — boxes with hundreds of documents and photos — to rediscover the case, alongside the neuropsychologist Alberto García Molina. At a time when the scientific community was divided between those who see the brain as a whole, and those who draw hard boundaries between the brain regions, Gonzalo proposed an intermediate hypothesis based on Patient M: the theory of brain dynamics, according to which the organ has its functions distributed in gradients, with gradual transitions.

Isabel Gonzalo, who is a physicist and professor emeritus at the Complutense University of Madrid, met Patient M during his visits to the family’s home. The man had been born in a village in the Spanish municipality of Ciudad Real. When he was resting, without major stimuli, he saw a terrifying backwards world, in which objects appeared in triplicate and tinged green. His auditory and tactile perception were also inverted, so that sounds and touches appeared in his mind on the opposite side. “M looked at his wristwatch from a