For a long time, people with schizophrenia have reported feeling as though their thoughts and actions were controlled by an outside influence, and people didn’t understand why. One experiment, involving crickets, may have shed some light on the neurology behind that feeling.

A new book, The Man Who Wasn’t There, takes a look at mental illness from the patient’s perspective, and along the way, it illuminates why people with schizophrenia feel like an outside force is in control of their actions.

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Take a moment, right now, and make note of all the places where you are touching your own body. Maybe you have your legs crossed, or your chin on your hand, or your arms resting against your sides. As you move, you may be conscious of the way your hands brush your legs, or your fingers rub together, but just slightly. You’d be much more conscious of someone else rubbing your fingers, or someone else’s hand on your leg, even if they touched you surreptitiously.

It’s extremely important to be able to distinguish between the sensations you receive due to your own actions, and the sensations that are caused by someone else’s. This distinction isn’t just a matter of experience, it’s a matter of physiology. Scientists decided to monitor the chirping of the singing cricket. Chirping is a way of finding mates and listening to competition, so it’s important that a cricket can listen past its own song to the chirps around it. When one specific neuron fired at the same time as the cricket’s wing movement, the crickets were able to do this just fine. When this neuron, called the corollary discharge interneuron, didn’t fire, the crickets didn’t register the song as their own.

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The same thing happens with people—albeit with a more complicated set of neurons. It’s a malfunction of a real, and necessary, function of the brain to distinguish between the physical input we get from our own actions and the input we get from other people’s actions. And it doesn’t only work one way.

In one study, both people with schizophrenia and neurotypical people played a video game. The games were, at certain times, controlled by scientists behind the scenes, who caused certain actions to lag, or for cursors to experience random turbulence. Both groups could judge their performance accurately, but the players with schizophrenia didn’t seem aware of when they were fully in control and then they were being controlled by the scientists.

So it appears there is an actual physical function in the brain that registers, and quietens, physical sensations that we believe are our own, but leaves the sensations that we believe come from others at full volume. People with schizophrenia often can evaluate their actions and thoughts, but those thoughts sometimes “feel” as though they come from an outside influence.

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Imagine someone comes in to your office every day, once a day, and puts a hand on your shoulder. When you complain about it, other people tell you that it’s your own hand on your shoulder. You get this information from multiple people, and you trust it. Intellectually, you can tell yourself, each time you feel it, that what you’re feeling is just your own hand. But that feeling remains.

[Source: The Man Who Wasn’t There, by Anil Ananthaswamy]

Top Image: Allan Ajifo

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