The Origin of Behavioral Bursts in Decision-Making Circuitry

From ants to humans, the timing of many animal behaviors comes in bursts of activity separated by long periods of inactivity. Recently, mathematical modeling has shown that simple algorithms of priority-driven behavioral choice can result in bursty behavior. To experimentally test this link between decision-making circuitry and bursty dynamics, we have turned to Drosophila melanogaster. We have found that the statistics of intervals between activity periods in endogenous activity-rest switches of wild-type Drosophila are very well described by the Weibull distribution, a common distribution of bursty dynamics in complex systems. The bursty dynamics of wild-type Drosophila walking activity are shown to be determined by this inter-event distribution alone and not by memory effects, thus resembling human dynamics. Further, using mutant flies that disrupt dopaminergic signaling or the mushroom body, circuitry implicated in decision-making, we show that the degree of behavioral burstiness can be modified. These results are thus consistent with the proposed link between decision-making circuitry and bursty dynamics, and highlight the importance of using simple experimental systems to test general theoretical models of behavior. The findings further suggest that analysis of bursts could prove useful for the study and evaluation of decision-making circuitry. Author Summary: It has long been observed that animal movement tends to come in bursts of activity. This has been seen in many animal species, ranging from small insects to even human activity patterns. The underlying mechanisms remain unknown, but recently a mathematical model showed that it could be due to priority-driven choice behavior. If the animals decide what to do next depending on the relative priorities of the choices at hand, the behavior becomes bursty, while if the animals simply act directly on cues coming from the outside, their behavior becomes less structured and more random. To test if decision-making processes affect behavior in bursts, we studied the fruit fly (Drosophila melanogaster), because of the powerful genetic tools available. We manipulated a part of the brain known as the mushroom body, and neurons that form the dopaminergic system, since both had previously been found to disrupt normal choice behavior in the fly. In particular we found that high levels of dopamine made the flies' activity pattern less structured, and that parts of the mushroom body circuitry also affected burstiness. Our findings are thus consistent with the idea that decision-making processes could be important for understanding animal and human activity patterns.