If you woke up in someone else’s body, would you feel like you or them? Swedish researchers recently explored just such a question, with intriguing results.

They found that when friends swapped bodies in a perceptual illusion, their beliefs about their own personality became more similar to their beliefs about the friend’s personality. 

The finding, they say, suggests that the close tie between our psychological and physical sense of self is also involved in functions like memory: when our mental self-concept doesn’t match our physical self, our memory can become impaired.

And that may be valuable when assessing psychiatric disorders such as depression or depersonalisation, where people feel an incoherence between their mental state and their bodies.

“We show that the self-concept has the potential to change really quickly, which brings us to some potentially interesting practical implications,” says Pawel Tacikowski from the Karolinska Institutet, first author of the team’s paper in the journal iScience.

“People who suffer from depression often have very rigid and negative beliefs about themselves that can be devastating to their everyday functioning. If you change this illusion slightly, it could potentially make those beliefs less rigid and less negative.”

For the study, the researchers fitted pairs of friends with goggles showing live feeds of the other person’s body from a first-person perspective and simultaneously applied touches to corresponding body parts so both could also feel what they saw in the goggles.

After just a few moments, the illusion generally worked. When they threatened a friend’s body with a prop knife, the participant broke into a sweat as if they were the one being threatened.

Before the body swap, participants were asked to rate their friend on traits such as talkativeness, cheerfulness, independence and confidence. Compared to this baseline, when they did the same during the swap they tended to rate themselves as more similar to the friend whose body they were in.

Participants also tended to perform worse on memory tests. Intriguingly, however, those who more fully embraced their friend’s body as their own and significantly adjusted their personality ratings to match how they rated their friend performed better on the tests than those who indicated they felt disconnected from their body.

The researchers say this could be because they had less “self-incoherence”, meaning that their mental and physical self-representations still aligned.

The study did have limitations, not the least, the authors note, that the memory task assessed only episodic recognition memory; that is, whether participants remembered encountering specific items during the preceding study session or not.

Nevertheless, they believe the findings demonstrate “that coherence between the bodily and conceptual self-representations is important for the normal encoding of episodic memories”.

The next step, Tacikowski says, is to formulate a more general framework for how the sense of self is constructed across the bodily and psychological levels.

“Now, my mind is occupied with the question of how this behavioural effect works: what the brain mechanism is. Then, we can use this model for more specific clinical applications to possibly develop better treatments.”