How the brain builds a social 'Self'

How do our brains distinguish between Self and Other? 'Self-ness' may be intrinsic to some fundamental signals in the brain, but it seems to be a property that can be lost or acquired through our experiences with other people.

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How does a human mind emerge from a brain?

To answer this, I think we need to consider evolution. What evolved as a consequence of the human mind? One answer is society.

If collective intelligence is the next evolutionary step after individual intelligence, then maybe we can rephrase our question:

How does a human mind emerge from a brain, such that societies emerge?

This question is more constrained than my original question, and hopefully it is easier to answer. It is the question that motivated my PhD.

When I was reading the social neuroscience literature, I was struck by how researchers were looking for brain processes that are specific for 'social cognition'. There seemed to be a pervasive undertone that 'social cognition' is special and fundamentally different from 'non-social cognition'.

I share the sentiment that social cognition may hold the key to some of the deepest mysteries of the human mind. However, I don’t think there are any good definitions out there for ‘social’ and ‘non-social’. I wanted to take an approach where I didn’t have to look for the ‘social brain’. Instead, I wanted to ask how fundamental, well-characterised processes in the brain could possibly enable societies to emerge? I assume that, for societies to emerge, my brain needs to represent the fact that other people exist, who are not me. How does the brain distinguish between Self and Other?

During my PhD, I developed the ‘probabilistic false belief task’. This cognitive task requires a participant to put themselves in the shoes of another person, and keep track of the other person’s beliefs, which, by design, are different from the participant’s own beliefs. The participant has to distinguish between their own beliefs, and the other person's beliefs. 

This is a computationally-inspired task, designed so that we can describe what is going on in the participant’s mind, mathematically, in terms of predictive processing. This is a computational framework that describes the brain as always trying to predict what will happen next. Every prediction is compared with the true outcome in the real world. The extent to which the prediction deviates from the truth (‘prediction error’) helps the brain to make the next prediction better than the last one. This framework has been used, with success, to explain sensory processing, reward learning, conditioning, motor learning, among many other cognitive domains in humans and other animals. This framework provided me with a language in which to pitch my hypotheses and questions, which were agnostic as to whether the processes were 'social' or 'non-social'.

When a person experiences a prediction error, there’s a particular pattern of activity in their brain. With my task, I could look at a participant's brain activity while they experienced a prediction error, and also look at the activity while they simulated the other person's prediction error.

We found that the brain uses distinct patterns of activity for prediction errors and 'simulated' prediction errors. This means that these fundamental brain signals contain information, not only about what’s going on out there in the world, but also about who is thinking about the world. This is information about the subjective sense of ‘Self’.

However, we also found that we could train people to make those brain-activity patterns for Self and Other either more distinct or more overlapping. If they became more distinct, participants got better at distinguishing their own thoughts from the thoughts of the partner. If the patterns became more overlapping, they got worse at distinguishing their own thoughts from the thoughts of the partner. 

This means that the boundary between Self and Other in the brain is not fixed, but flexible. The brain can learn to change this boundary. This might explain the familiar experience of two people who spend a lot of time together and start to feel like one single person, sharing the same thoughts.

Experiencing inappropriate Self-Other boundaries underlies many mental health disorders, such as schizophrenia and borderline personality disorder. Our research shows that there is a capacity to relearn these boundaries. I hope this capacity can be harnessed for therapeutic purposes. 

Sam Ereira

MB-PhD student , University College London

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