How does the brain make decisions when faced with conflicting options?

Every day, we make choices that involve balancing opportunities with risks—but what’s actually happening in our brains as we make these decisions remains largely unknown. A central mystery in neuroscience is how the brain evaluates conflicting options and prioritizes specific actions. Evidence suggests there are sex differences in decision-making and unique vulnerabilities to neurological disorders across genders. Therefore, understanding how the brain makes decisions across contexts and genders holds important medical, economical, and societal benefits.

Studying decision-making in mammals is challenging due to the brain’s complexity, but it is feasible in the fruit fly Drosophila, where single cells and circuits can be easily observed and manipulated. Capitalising on these advantages, we discovered a fascinating brain mechanism that allows flies prioritise behaviours during conflicting situations (Cazale-Debat et.al Nature, 2024 doi: 10.1038/s41586-024-07890-3).

When animals, including humans, are deeply focused on something they desire—they may become less aware of potential dangers around them. This phenomenon, often referred to as “love blindness,” is a widespread behavioural tendency where the pursuit of a valued reward, like a mate, can overshadow possible risks. In the animal world, this kind of focus can help increase the chances of finding a mate and reproducing, but it also makes individuals more vulnerable to threats, such as predators.

In our study, we explored how the brain balances risk and reward during courtship, focusing on male fruit flies. We discovered a neural mechanism controlled by dopamine, a chemical linked to reward and pleasure, which allows the flies to reduce their sensitivity to danger as they get closer to mating. In the early stages of courtship, visual signals alert the flies to nearby threats, activating certain neurons that cause the flies to stop courting. This response is mediated by serotonin, another brain chemical that temporarily inhibits the courtship drive to ensure survival.

However, as the male flies advance in the courtship process, the brain gradually shifts gears. Dopamine levels rise, which reduces the response to threats, allowing the flies to stay focused on courtship instead of fleeing from danger. By tracking brain activity, we observed that the closer the flies get to mating, the higher the dopamine levels rise, eventually blocking the pathway that would normally alert them to visual threats. This allows the flies to “tune out” distractions and prioritise mating.

In essence, dopamine acts as a sensory filter, adjusting the flies’ perception of threats based on their proximity to achieving their goal. This filtering system enables the brain to prioritise between competing actions, choosing reproduction over survival when it matters most.

This PhD project will take this discovery further, aiming to answer key questions: (i) Does this dopamine-driven filtering mechanism also exist in females, and are there sex-specific differences? (ii) Is this neural mechanism applicable to other high-stakes decisions beyond mating versus predator avoidance? (iii) Is this neural mechanism an evolutionarily conserved strategy?

As a PhD student on this project, you’ll work at the cutting edge of neuroscience, using state-of-the-art techniques including advanced genetics, neural circuit tracing/connectomics, multiphoton imaging to capture neural activity in live, synaptic tracing, behaving flies, optogenetics, CRISPR for gene editing, and custom coding for data analysis. You will collaborate with researchers working in Germany, UK and Switzerland.

This project offers an unprecedented opportunity to uncover decision-making processes during conflicts at remarkable molecular, cellular, and neural circuit level, revealing fundamental principles of brain function across species and sexes.

For more information about the Rezaval lab and research please visit: https://www.rezavallab.org/

Please contact Prof Rezaval directly with a cover letter outlining your interest, your background, and why you wish to join her lab in particular.