At 19, AB got viral meningitis, an infection of the membranes around the brain. For a month thereafter, she could see colors with musical notes but they would be the wrong colors. She again recovered. But then she got another concussion, which moved the colors she saw from the center of her field of vision to the side. Yet another concussion made the colors more intense but somehow off. According to the study, it didn’t affect the actual colors she saw of objects in the real world, but the change in her synesthesia was still distressing. The colors AB perceived through synesthesia were as real to her as the colors of real objects; seeing different colors with the same musical notes was like waking up one day to find apples blue.

Things got really weird after she was struck by lightning two months later. This, understandably, increased her anxiety, and she started seeing strange colors like golds and silver along with colors that were possibly “not even real colors,” she told the researchers. Xanax calmed her, but it also muted the colors she perceived. Later, when she started getting seizures, medication again completely suppressed the colors. Her synesthesia returned to normal the next year, and the colors she associated with notes and people were the same as before the meningitis and lightning episodes.

Drugs can sometime induce synesthesia in non-synesthetes, so the idea that synesthesia can come and go is not surprising. “It’s almost in synesthesia folklore that synesthesia can weaken with certain types of drugs and depression,” says David Brang, a psychologist at the University of Michigan who studies synesthesia but was not involved in this case study. What’s remarkable, says Brang, is that AB’s color associations came back and remained consistent, despite all the medications and head trauma. In a second case also presented in Mitchell’s paper, a man referred to as CD lost his synesthesia for eight years when he started taking antidepressants for Seasonal Affective Disorder, only to have it return in full force when he stopped.

Synesthesia has two competing—though not mutually exclusive—explanations in neurobiology. In one, people with synesthesia have extra connections in their brains, connecting for example their auditory cortex with their visual cortex. In the second, everyone has these connections between different parts of the brains, but they’re usually unactivated. These connections may be disinhibited—as in un-unactivated—in people with synesthesia. The cases of AB and CD do not readily point to one explanation over the other. Perhaps the drugs and head trauma altered the wiring of their brains; perhaps it altered which connections were active. Perhaps both.

What the cases do neatly illustrate is the subjectivity of color, and by extension, of all our perceptions. If you can hear a note and see turquoise one day and hear the same note but see no color the next, then you have to conclude color is not intrinsic to the note. Even the color we see from real objects are our brains’ interpretations of wavelengths of light bouncing off that object. (Cough, The Dress.) That’s why AB could report perceiving colors that were “not even real colors.” “It’s a really fascinating insight into how the brain generates internally a representation of a color,” and how the brain could generate it wrong, says Mitchell.