What Waking Up in a Friend’s Body Does to Your Mind

Freaky Friday has been made into a movie four times, and its storyline betrays a belief many of us hold about ourselves. We think of our "self" as a constant essence that resides within the shell of our bodies. If we happened to awake in another's body, we would still be the same person, just inhabiting a different shell; in the early aughts version of the story, Lohan's character was still an angsty teenager even as she inhabited the body of Curtis's character, previously  a moralistic psychotherapist. 

But a new study, out today in iScience, an open-access journal from Cell Press, challenges the notion that our “selves” are independent of the bodies we exist in. The study used a perceptual illusion to make friends feel like they had swapped bodies, and found that during the illusion they changed the way they rated their own personalities, self-reporting traits they had previously attributed to their friend. 

The study isn't trying to debunk Freaky Friday, but simply to get at some basic questions about self-perception and conscious existence in a physical body: How is it that we feel like our body is our own? What does that body ownership have to do with our sense of self, and what we think about ourselves and others? 

Body illusions, where people experience ownership of another body, have been an important cognitive neuroscience tool over the past two decades, used for investigating these questions. They can be induced in several ways, with virtual reality, clever positioning of cameras, or just a prop arm and some carefully placed sensory stimulation. The illusions can be powerful—in one study, people experienced being in another body while facing themselves, and then shook their own hand from an outsider's perspective. 

This new research further adds to the growing understanding that when people’s perceptions of their bodies change, it can change the way they think and feel. After having an out-of-body experience through virtual reality, people report a reduction in the fear of death. An illusion where people were made to feel invisible led to feeling less social anxiety when standing before a crowd. When people embodied a four-year-old child’s body using virtual reality, it led them to unconsciously associate themselves with child-like traits, and view the world around them as larger. 

These kinds of illusions could one day be applied as a therapeutic tool for conditions that involve body misrepresentation or depersonalization, like dissociation, eating disorders, chronic pain, schizophrenia, phantom limb pain, and more. 

Body swapping reveals how important the body is for creating and maintaining a sense of self. It suggests that our brains strive for coherence, and constantly update the way we view our “self” as we get new information (like, from illusions). 

“These new technologies have really allowed us to see to what extent our experience of ourselves, especially our bodily self, is surprisingly malleable,” said Jane Aspell, a cognitive neuroscientist at Anglia Ruskin University in the U.K., who was not involved in the new study. 

Olaf Blanke, a neuroscientist and chair in Cognitive Neuroprosthetics at the École Polytechnique Fédérale de Lausanne, who was not involved in the new study, said that traditionally, neuroscience has examined other influences on the concept of self.

“The body has been ignored,” Blanke said. “Science [and] philosophy have traditionally mostly associated the self with reflective cognitive aspects of the mind, but these recent studies reveal that bodily perceptual signals are fundamental for self-consciousness.”

"Rubber hand illusions" helped spur this line of research. They showed that if you put a fake hand near you and hide your own hand, you can trick yourself into thinking the fake hand is your own. This is usually achieved by someone touching the fake hand while you watch, and touching your real, out of sight, hand at the exact same time. 

“One moment you are looking at an inanimate object, and the next moment the object 'comes alive' as one experiences the rubber hand to be one’s own hand,” wrote H. Henrik Ehrsson, the senior author on the new paper, in a book chapter on body ownership. 

These illusions can trigger real changes in the body. In 2008, a study found that when a person experiences the rubber hand illusion, it changes the homeostatic regulation of their real hand—for example, the skin temperature of their real hand decreases, and the amount it changed by was correlated to how intensely they were experiencing the illusion. If the fake hand is threatened, a person will have a similar physical reaction as if their real body was being attacked. 

The rubber hand illusion shows that the way we perceive our bodies is a collaboration of many sensory inputs combining together—all of the different parts of our bodies, what we see and hear, and where it’s all put together in our brains. That process impacts our sense of self too. 

“It is only relatively recently that we have begun to discover the striking influence that basic body perception can have on more complex cognitions regarding the self,” said Lara Maister, a lecturer at the School of Psychology at Bangor University in the U.K. who was not involved in the study. 

These beliefs are important. “You can think of them as a ‘reference point that helps us to decide, for example, whether we are going to be a good fit for a new job, or whether we are going to connect well with a newly met person,” said Pawel Tacikowski, a cognitive neuroscientist at the Karolinska Institute in Sweden, and the first author on the new study.

For the experiment, Tacikowski and his colleagues had pairs of friends lay on two beds wearing head-mounted goggles. They saw live recordings from cameras placed just above and behind the other person’s head—so that when they looked down, instead of seeing their own bodies, they saw their friend’s body.

Just like the rubber hand and other body illusions, the researchers used touch to solidify the illusion of swapping bodies. The researchers measured if the illusion worked by measuring a person’s physical reaction when their friend’s body was “threatened” with a fake knife—they reacted as if their own body was about to be harmed. 

Before they swapped bodies, the friends rated each other’s personalities, like how talkative, cheerful, or confident they were. While embodying their friend, they rated themselves more similarly to the traits they had previously ascribed to their friend. 

Interestingly, the body swap also triggered a change in memory—some participants did worse on memory tests they took during the illusion, but not all of them. The people who were better at embracing their friend’s body and personality did better on memory tests, suggesting that memory can be impaired when a person’s body clashes with their concept of self. Previous studies have also shown that body illusions impair memory. 

“It highlights how important a coherent, complete multidimensional self structure is for the encoding of memories,” Maister said, adding that this has implications for understanding memory deficits in people who experience distortions in self-representation, for either neurological or psychiatric reasons. 

“If your representation of self is disturbed, it's not that surprising that that should also have some disruption on memory as well,” Aspell said.

“Embodied cognition is a compelling framework that highlights the importance of our body in the shaping of our mind, but how exactly this comes to happen is still largely unknown," Tacikowski said. "I think we are only beginning to understand what brain mechanisms might be at play here.” 

In our everyday lives, the way people look and what we think about them are already linked. It’s been shown that when we see people who look physically similar to us, we believe that they’re similar to us in personality or beliefs. Maister said that studies like Pawel’s suggest we don’t just push these assumptions onto others, but onto ourselves. 

“If our representation of our physical appearance is updated by a body illusion, it might update our self-beliefs to be consistent with our altered appearance, reflecting the brain’s constant drive for coherence across representational levels,” she said. This is consistent with the “Proteus effect,” when people’s behaviors and thinking patterns are influenced by the physical appearance of an avatar they use in a virtual environment— like a video game. 

All these effects can be subtle, but there's hope to apply this knowledge in the future to change people's perspectives about others.  Studies have shown that when white people inhabit a Black virtual body, their implicit bias scores—which measure subconscious attitudes towards race—go down. In 2018, researchers had domestic violence offenders embody a female victim, which resulted in significant improvements in their recognition of female emotions. Maister said that the approach in the current study—embodying someone you know personally—might be useful one day in family or couples therapy, where thinking that you’re similar to another person you know could increase closeness. 

Researchers have also considered how to apply body illusions to health, like for anorexia, when people can be experiencing a disruption in their sense of self-representation and seeing themselves as overweight as they get thinner and thinner. Aspell has also done research on chronic pain, showing that inducing body illusions in chronic pain patients can reduce pain by almost 40 percent.

Tacikowski said that next, he’ll be investigating how long these kinds of effects can last, and if repeating the experiment again on the same person would enhance the changes in cognition. The take-home message, Aspell said, is that neuroscience needs to include the body in its investigations into perception, consciousness and the self. 

“You can’t just study the brain in a vat,” she said. “The brain exists in the body and in the environment. If you look at it separated from those things, you get a really false picture of it. You're only getting half the picture. It's not just the brain sending the body commands, but the fundamental nature of the brain is massively shaped by the body. I think any aspect of neuroscience that ignores that is going to be fundamentally incomplete.”

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