Reward from bugs to bipeds: a comparative approach to understanding how reward circuits function

Abstract

In a complex environment, animals learn from their responses to stimuli and events. Appropriate response to reward and punishment can promote survival, reproduction and increase evolutionary fitness. Interestingly, the neural processes underlying these responses are remarkably similar across phyla. In all species, dopamine is central to encoding reward and directing motivated behaviors, however, a comprehensive understanding of how circuits encode reward and direct motivated behaviors is still lacking. In part, this is a result of the sheer diversity of neurons, the heterogeneity of their responses and the complexity of neural circuits within which they are found. We argue that general features of reward circuitry are common across model organisms, and thus principles learned from invertebrate model organisms can inform research across species. In particular, we discuss circuit motifs that appear to be functionally equivalent from flies to primates. We argue that a comparative approach to studying and understanding reward circuit function provides a more comprehensive understanding of reward circuitry, and informs disorders that affect the brain’s reward circuitry.

Keywords:

• Behavior
• dopamine
• functional conservation
• neuromodulators
• neuropeptides
• neurotransmitters

Acknowledgements

We thank Michael Frank, Galit Ophir, Julie Kauer, Abigail Polter, and Marla Sokolowski for helpful comments on earlier versions of this manuscript and Michael Bruchas and Jeremiah Cohen for several reference suggestions.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Funding information

K.R.K. and K.M.S. are supported by the Richard and Susan Smith Family Foundation, Newton, MA, a Brown Institute for Brain Science, Center for Nervous System Function, COBRE Project Leader Award (NIGMS P20GM103645) and a Rhode Island Foundation Medical Research Award (20144133).