How the brain detects the gap between expectations and reality

The claustrum is a thin sheet of neural tissue deep inside the brain that is connected to almost the entire cerebral cortex. Because of this, it can theoretically influence information processing throughout the brain, but its functions have remained a mystery until now. In a new study, researchers decided to investigate whether the claustrum is involved in aversive learning—that is, in how a person learns to recognize and avoid unpleasant outcomes.

To do this, the researchers took advantage of a unique opportunity: Seven patients with epilepsy already had electrodes implanted in their brains; these were placed as part of routine clinical monitoring to identify the seizure focus. The activity of individual neurons was recorded from these electrodes in three areas: in the claustrum, the anterior cingulate cortex (which helps assess the results of actions and adjust behavior), and the amygdala (which is responsible for emotions and learning from threats).

While the recordings were being made, the participants played a simple computer game: they had to steer a virtual spaceship through gaps in approaching asteroid belts. The researchers deliberately altered the frequency at which safe passages appeared, so that the participants had to constantly revise their expectations in order to avoid crashing into asteroids.

Then the scientists compared neural activity with how the game conditions changed and how well the players avoided collisions. Using a mathematical model, they calculated at which moments the participants’ uncertainty increased (i.e., how unsure they were about the outcome) and a prediction error arose (the difference between the expected and the actual result).

It turned out that different groups of neurons responded to different events: some were activated when a belt of asteroids appeared on the screen, while others were activated when it became clear whether a collision had been avoided. At the same time, the claustrum and the anterior cingulate cortex tracked hidden variables — uncertainty and prediction error — but they did so at different times.

The anterior cingulate cortex sent signals about uncertainty both between rounds and during the active phase, when it was necessary to dodge the asteroids. In the claustrum, signals related to uncertainty and prediction error were mainly noticeable precisely at the moment of active evasion, when asteroids were approaching the ship. The amygdala, by contrast, showed almost no change in activity in response to these hidden variables.

The claustrum does not so much experience a threat as it records how reality diverges from expectations, and it does this precisely during tense moments when decisions need to be made quickly. The study does not prove that the claustrum itself causes the brain to change expectations. It shows that this area tracks uncertainty and prediction errors.

The authors believe that these data open the way to a better understanding of the role of the claustrum, as in the future its function can be studied in other tasks where the brain has to update its internal models of the world.