This terrifying disorder turns people into zombies, into living, breathing ghosts; they believe they died, or never existed. And somewhere in their brains may be the key to human consciousness.

By Erika Hayasaki
Photographs by Eunice Adorno for Matter
Conceptual photographs by Marlous van der Sloot

I’ve come to Mexico City to find the real walking dead.

Glancing around the courtyard of the walled-off National Institute of Neurology and Neurosurgery, you might think this place is filled with them. Two dozen patients chew and pick at their lunches of yellow chicken legs and bread rolls, while others slump listlessly around a courtyard. Some are catatonic. Blank. Others are simply bodies in beds, slumbering beneath the sheets, unconscious in the afternoon. One woman with flared nostrils presses a bony shoulder into her mattress, cradling her emaciated body.

Most of the patients here have been diagnosed with garden-variety neurological disorders: schizophrenia, dementia, psychosis, severe depression, or bipolarism. But the ones I am searching for are…