Final Report Summary - C.O.C.O. (Circuits of con-specific observation)
A great deal is known about the neural basis of learning about threats. However, many animal species are able to use social cues to recognize threats, a defense mechanism that may be less costly than learning from self-experience. However, the mechanisms by which animals use social information to regulate their defensive responses remained largely unexplored. With this project we unraveled key elements in a neuronal circuit that mediates the response of rats the display of defensive behavior of others and how their own experience with aversive stimuli contributes to this response. This work advanced our knowledge on the regulation of defense mechanism, by establishing a link between the circuit that underlies learned fear of arbitrary auditory cues to that used for natural sound cues. In addition, our studies brought novel insights into the role of self-experience and how learning about the behavior of oneself determines our response to the behavior of others, contributing to the understanding of the processes that are at the basis of social behavior, having implications for a number of diseases and conduct disorders where social behavior is impaired. Finally, this project allowed the establishment of a new line of research that uses Drosophila melanogaster as a model system to study how the brain uses defense behaviors as signals of danger and how it contributes to defense mechanisms at the population level. We found that fruit flies, as several vertebrate species, make rapid decisions of whether to freeze avoiding detection or attempt to flee when exposed to an inescapable threat. In addition, we found motion plays a crucial role in the regulation of defensive behaviors. Not only the speed at which the fly is moving partially dictates whether a fly will freeze or flee, but they also regulate their freezing responses by the motion of others neighboring flies. Finally, we have identified specific neurons crucial for the expression of freezing, and a class of visual neurons that mediate the regulation of freezing behavior by the movement of others. Importantly, prior to our studies no known behavioral function had been reported to either neuronal type. We believe our work paves the way to the mechanistic underpinnings of collective defensive behaviors, which are likely to follow principles shared across a wide range of animal species.