A previously unknown type of neuron has been identified by scientists at the University of Cambridge, that actively and spontaneously simulates mental decision processes when social partners learn from one another.
Scientists discovered these simulation neurons in the amygdala, a collection of nerve cells in the temporal lobe of the brain. These neurons are responsible (in animals and potentially also humans) to reconstruct their social partner’s state of mind and thereby predict their intentions.
The analysts proceed to estimate that if simulation neurons became dysfunctional this could limit social cognition, an indication of autism. Conversely, they propose overactive neurons could result in an exaggerated simulation of what others may figure, which may assume a role in social anxiety.
The study’s lead author, Dr. Fabian Grabenhorst from the Department of Physiology, Development, and Neuroscience, says: “We started out looking for neurons that might be involved in social learning. We were surprised to find that amygdala neurons not only learn the value of objects from social observation but actually use this information to simulate a partner’s decisions.”
“Simulating others’ decisions is a sophisticated cognitive process that is rooted in social learning. By observing a partner’s foraging choices, for instance, we learn which foods are valuable and worth choosing. Such knowledge not only informs our own decisions but also helps us predict the future decisions of our partner.”
Until now, it has been suggested that simulation is the mechanism by which humans understand each other’s minds. Yet, this complex process on the neural basis remains unclear.
The amygdala is an almond-shaped set of neurons located deep in the brain’s medial temporal lobe. Moreover, it is known for its diverse roles in social behavior and has been implicated in autism. Until now, however, it was unknown whether amygdala neurons also contribute to advanced social cognition, such as simulating others’ decisions.
During the study, scientists recorded activity from individual amygdala neurons as macaque monkeys took part in an observational learning task. Sat facing each other with a touch screen between them, the animals took turns in making choices to obtain rewards. To maximize their fruit juice reward, the animals were required to learn and track the reward probabilities associated with different pictures displayed on the screen.
Animals were able to observe their partner’s choices so that they could learn the pictures’ reward values. Once the pictures switched between them, the observing animal could make use of this knowledge when it was their turn to choose.
Scientist found that at the point when an animal observed its accomplice, the observer amygdala neurons appeared to play out a decision calculation. These neurons previously looked at the reward values of the partner’s decision choices before signaling the partner’s possible choice, steady with a simulated decision procedure. Essentially, this activity patterns occurred suddenly, well before a partner’s choices and without decision requirement for the observer.
Based on the outcomes, scientists designed a computer model of the amygdala’s neural circuits involved in social cognition. The model works by showing how specific types of neurons influence one another and suggests that the amygdala contains a ‘decision circuit’ which works out the animal’s own choices and a separate ‘simulation circuit’ which computes a prediction of the social partner’s choice.
Grabenhorst said: “Simulation and decision neurons are closely intermingled within the amygdala. We managed to distinguish between them and their different functions by carefully examining one neuron at a time. This would not have been possible with human brain imaging techniques that measure the averaged activity of large numbers of neurons.”
“We think that simulation neurons are important building blocks for social cognition — they allow animals to reconstruct their partners’ mental decision processes. Simulation neurons could also constitute simple precursors for the amazing cognitive capacities of humans, such as ‘Theory of Mind’.”
The scientists suggest that if simulation neurons were dysfunctional or completely absent, this could impoverish social behavior.
Grabenhorst says: “If simulation neurons don’t function properly, a person might not be able to relate very well to the mental states of others. We know very little about how specific neuron types contribute to social cognition and to the social challenges faced by individuals with autism. By identifying specific neurons and circuit mechanisms for mental simulation, our study may offer new insights into these conditions.”
The study is published today in journal Cell.