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A young man in a gray flannel robe sits calmly at a table, in front of a featureless black box. He’s wearing a cap that looks like it’s made of gauze bandages. A bundle of wires snakes out of it, emerging from the back of his head. He’s waiting for something.

A researcher in a white lab coat walks up to the table and stands silently for a moment. The man stares at the box. For a moment, nothing happens. Then the man blinks and appears slightly abashed. The researcher asks what happened.

“Just for the very first second,” he says, “I saw an eye—an eye and a mouth.”

The researcher swaps the box for a different object. This time it’s an orange soccer ball. There’s a beat, and again it’s clear that something has happened inside the man’s head. “How do I explain this?” he says. “Just like the previous one, I see an eye—an eye and a mouth, sideways.”

Strictly speaking, this man is a cyborg. His fusiform gyri, meandering ridges that run along the bottom of the brain on each side, are studded with electrodes. His doctors implanted them because they thought they’d help trace the cause of the man’s seizures. But the electrodes also offer a rare opportunity—not just to read signals from the brain but to write them to it. A team of neuroscientists, led by MIT’s Nancy Kanwisher, is investigating the so-called fusiform face area, which becomes active when a person sees a face. Their question is, what if they reverse the pumps? Intentionally activate that area—what would the man see?

You don’t have to be a cyborg to know that you should never trust your lying mind. It conceals from you, for example, the fact that all your perceptions are on a delay. Turning photons into sight, air-pressure fluctuations into sound, aerosolized molecules into smells—that takes however long your imperfect sensory organs need to receive the signals, transduce them into the language of the brain, and pass them on to the shrublike networks of nerve cells that compute the incoming data. The process isn’t instantaneous, but you’re never aware of the zillions of synaptic zaps going on, the electrochemical fizz that makes up your mind. The truth is it’s stagecraft—and you’re both director and audience.

You perceive, or think you perceive, things that aren’t “really there” all the time—that aren’t anywhere except inside your head. That’s what dreams are. That’s what psychedelic drugs do. That’s what happens when you imagine the face of your aunt, the smell of your first car, the taste of a strawberry.

From this perspective, it’s not actually hard to incept a sensory experience—a percept—into someone’s head. I did it to you for the first few paragraphs of this story. I described how the cyborg was dressed, gave you a hint of what the room looked like, told you the soccer ball was orange. You saw it in your mind, or at least some version of it. You heard, in your mind’s ear, the research subject talking to the scientists (although in real life they were speaking Japanese). That’s all fine and literary. But it’d be nice to have a more direct route. The brain is salty glop that turns sensory information into mind; you ought to be able to harness that ability, to build an entire world in there, a simulation indistinguishable from reality.