The secret of a smile

Babies learn at a very young age to smile at those who smile at them. Immediately afterwards, they also learn that if they take the initiative and smile at someone - they will receive a smile back from them. Understanding the interrelationships between the facial expressions of the self and the facial expressions of the other is important even in old age: the meaning of receiving a threatening face from a person to whom you smiled is completely different from a case where you stare at him aggressively. That is, in order to successfully decode complex social situations, the facial expressions of all the participants must be recognized - not only those directed at you, but also your own. This fact sounds, perhaps, self-evident, but while many studies deal with the brain mechanisms that decode faces and emotional facial expressions of others, the question of how the brain decodes the facial expressions of the self has hardly been investigated until now.

A study conducted recently in the laboratory of Dr. Roni Paz, from the Department of Neurobiology, provides for the first time an answer to this question, and sheds light on the manner in which the integration between the information concerning the "other" and the information about the "self" is carried out. The findings also open up new research paths to examine cases where the processing of social-emotional information fails - as in the case of autism.

The research team, which was led by research student Uri Levana, and included Jennifer Resnik and Yossi Shohat, created a unique experimental set-up, where two monkeys stand facing each other, and have a natural and spontaneous interaction between them - without any intervention on the part of the scientists. Between the monkeys there was a gravel screen, the opening of which - for a few seconds - encouraged communication between the animals: the monkeys would communicate non-verbally, through facial expressions, as they usually do in nature. The scientists noticed three main facial expressions: a positive expression, characterized by the smacking of the lips and the contraction of the muscles around them, a threatening expression, characterized mainly by the contraction of the eyebrows and increased eye movements, and a neutral expression, which was observed when the screen was closed, when no interaction took place. During the experiment, the electrical activity of individual nerve cells in the brain was measured.

The scientists chose to focus on two areas of the brain - the amygdala, and a certain area in the cerebral cortex, which is known to be involved in processing emotional information and reacting to negative and positive faces. Indeed, the findings showed that not only are these two areas also responsible for deciphering the facial expressions of the self, but that these are also the same nerve cells. The distinction between electrical signals related to the processing of information about one's own face and those responding to the "other" face was made possible thanks to a very precise measurement, with a resolution of tens of milliseconds. It also became clear that the reaction of the nerve cells to the facial expressions of the self occurs in a very specific time frame, almost simultaneously with their creation. In other words, the amygdala knows about the smile even before it happens. The neural signal is sent to the amygdala directly from the brain during the creation of the facial expression, providing it with the right background and context to analyze the other's faces in a timely manner. Thanks to the close overlap between the networks in the brain that decode the faces of the self, and those that decode the faces of the other, the amygdala can receive all the relevant data, and quickly create a complete and accurate picture of the social situation. The findings were published in the journal of the American National Science Association (PNAS).

The close connection that the scientists discovered between the decoding of the facial expressions of the self and those of the other led the scientists to ask themselves, whether the same nerve cells are also involved in social learning, that is, learning through observing others. They plan to use the experimental setup they developed, which encourages natural interaction between animals, to better understand this type of learning. For example, when an animal learns through classical conditioning, does the animal watching it learn the same? Is there a network of nerve cells in the brain that learns from observation?

Another future research direction is related to neuropsychiatric disorders characterized by poor social communication, such as autism. Autistic people have difficulty creating emotional and social situations and understanding them, and studies have revealed abnormal activity of the neural network in them, which was at the center of the current study. Deciphering the mechanisms that enable the production and analysis of social and emotional situations may help in understanding the causes of defects in the development and activity of this type of neural networks. However, good models for complex neuropsychiatric disorders are currently still lacking. "The unique experimental setup we developed in this study can be used as a basis for creating a natural model for autism," says Dr. Paz. "It combines a natural and versatile social behavior unique to primates on the one hand, with complex neural networks that developed in primates, on the other hand."

personal

Yossi Shochat, technician and director of Dr. Roni Paz's laboratory, is a man of animals. As a child, he used to go down to the beach after storms, collect injured seagulls, and treat them at his home. Birds, dogs and insects also crowded the balcony of the house in Kiryat Haim, much to his mother's dismay. At the age of 25, this closeness and devotion led to a disaster: a camel, on which children were riding, suddenly began to go berserk, and Yossi, who approached to help, was attacked by it and fatally injured. He was paralyzed for a long time, but after a long rehabilitation process he came back strong - contrary to all the doctors' estimates. This medical miracle, he says, happened thanks to the animals. "The relationship with the animals was necessary for me to overcome the physical difficulties, and also the difficult mental state I was in." As a result of the injury, he was indeed forced to give up his studies in the Department of Animal Science at Oranim College, but not the unmediated connection with all kinds of four-legged and flying creatures. The injury also deprived him of the foreign languages ​​he knew, English and Arabic - these days he is relearning them, but not his mother tongue, nor the non-verbal language in which he communicates with animals.