Fifteen years ago, a string of women at a neurological hospital in London all showed signs of the same strange illness. Some were stiff and stuporous, while others were experiencing seizures or issues with movement. But their experiences had all begun with what seemed like textbook episodes of psychosis, complete with agitation, hallucinations and delusions. In the throes of those symptoms, some had gone to emergency departments or psychiatric hospitals. Their early notes read to neuropsychiatrist Thomas Pollak as classic cases of mental ill health. But it turned out that these people actually had a condition called autoimmune encephalitis, inflammation of the brain caused by an assault from the immune system. The fact that an autoimmune condition could produce psychosis shattered the usual divide between psychiatric and neurological illnesses and “kind of blew my mind”, says Pollak. In the years since, Pollak, now at King’s College London, has helped define an emerging field of study, one beginning to show that autoimmune disease plays a larger role in mental illness than conventional wisdom suggests. This link …