Love or war? - neural circuits and decisions

Abstract

Behaviors are sophisticated motor responses to complex stimulus. The study of innate robust behaviors has resulted in the identification of neural circuits behind them and has shed light on how these circuits function. Importantly, while innate behaviors determine the evolutionary success of species, they also need to adapt to the internal state of the animal and the environment. The study of Drosophila melanogaster behaviors, in particular male courtship and aggression, has been paramount to learn circuit function and decision making. These sexually dimorphic behaviors are genetically controlled through the expression of sex-specific gene isoforms which translate into dimorphisms between the female and male neural circuits. In addition, since according to environmental stimuli males will have to choose between mating or fighting, the neural circuits regulating these behaviors are intimately related. Multisensory integration into a cluster of neurons that work as a switch will determine whether the male courts or fights the conspecific fly it encounters. Once this switch favors one behavior or the other, the animal is committed to that particular motor pattern. However, not every time a male encounters a female it courts her, or every time it comes across another male aggression is triggered. The internal state of the animal plays an important role in decision making through neuromodulation. Neuropeptides and hormones among others can act on the circuit to enhance or dampen sensitivity at the level of sensory inputs and/or integration nodes. This way robust genetically hardwired behaviors can be flexible and coordinate with the environmental conditions and the internal state of the individuals. Importantly, the general concepts and functional strategies described in the fly are also present in other vertebrates such as mice, and thus could be conserved in others organisms.