The Function of Brain Lateralisation in Drosophila Decision Making

Abstract

A central question in cognitive neuroscience is aiming at a better understanding of the neural structures responsible for decision-making and the integration of relevant information. While much work has been done in humans and mammals describing decision-making influenced by different states of motivation, we know very little about the underlying neural circuit organization and function [1].

In my research project, I combine the “Drive Theory” to describe the motivational state of hunger, and the neurocomputational model of decision-making to guide my search for underlying neural structures [1], [2].

We decided to use the neurogenetic model Drosophila melanogaster (fruit fly) as the powerful experimental system of targeted gene knockouts is available for it and its nervous system being smaller than those of mammals make it an ideal candidate for researching motivated decision-making.

The drive theory posits that initially, from a sated state, the physiological need of an animal increases until it appears as a drive and compels it to reduce this state of motivation. Once the animal found the opportunity to reduce its drive, it would engage in consummatory behaviour until it returns to a sated state [1]. The neurocomputational model of decision-making posits that an animal needs 5 different systems working together to produce a decision in a motivated situation. It has to track its internal state, identify the decision-situation, select an action while evaluating possible outcomes and finally learn from the encounter [2].

Several potential systems have been described in Drosophila Melanogaster that could coordinate hunger drive with others and execute decision-making. In our research, we focused on a central brain circuit that, based on tracking the animal’s internal state, controls sugar choice when the fly is hungry. One of its parts, the SA^uni neurons innervate the AB neuropil only in the right hemisphere in most of the wild type brains. A function of their laterality has been described in the context of long-term memory formation, but nothing is known if asymmetric SA^uni neuron innervation is critical for decision making in feeding behaviour [3].

In my research, I aimed at finding out how laterality will affect the circuit’s functionality. I compared food preference of wild type Drosophila flies with asymmetrical brains with mutant lines in which central brain asymmetry is reduced. I knocked out Wnt4 as it has been implicated to control laterality and compared the results of a sugar-choice test with wild-type flies. The results will indicate a potential additional function for the Wnt signalling pathway and will give an idea on how laterality impacts decision-making.

References

[1] J. Reeve, Understanding motivation and emotion, 5th ed. Hoboken, NJ : John Wiley & Sons, 2009.

[2] A. Rangel, ‘Regulation of dietary choice by the decision-making circuitry’, Nat. Neurosci., vol. 16, no. 12, pp. 1717–1724, Dec. 2013, doi: 10.1038/nn.3561.

[3] P.-Y. Musso, P. Junca, and M. D. Gordon, ‘A neural circuit linking two sugar sensors regulates satiety-dependent fructose drive in Drosophila’, Sci. Adv., vol. 7, no. 49, p. eabj0186, 2021, doi: 10.1126/sciadv.abj0186.