To mate or to flee: neural mechanisms underlying action-selection

Life demands that we make innumerable decisions on a daily basis. For instance, we are often exposed to conflicting situations where we must prioritise one goal over another. Such decisions can affect our everyday life and, collectively, influence how our society evolves. Furthermore, action-selection processes are impaired in neurological disorders, such as addiction, Parkinson's disease, and Alzheimer's disease. How does the brain evaluate the available options and select the most appropriate action for each situation? We know that cues conveying information from the outside world must be constantly assessed and used in combination with internal needs to guide appropriate behavioural choices. However, the neural processes leading to this internal evaluation remain unknown.

Understanding how different neurons contribute to optimal action-selection will help us advance our knowledge of how the brain works, and what goes wrong in disease. The complexity of the mammalian brain has made it difficult to fully understand the neural circuits of action-selection. However, we can take advantage of organisms with smaller brains that must also deal with behavioural conflicts on a daily basis. In particular, the fruit fly Drosophila melanogaster offers a great opportunity to investigate the neural mechanisms of action-selection. Thanks to sophisticated tools available in the fruit fly, we can interrupt specific genes, as well as visualise and manipulate individual neurons with great resolution. With these tools, we can study how the fly brain responds when there are conflicting options available, and how it chooses amongst them. For instance, how does a fruit fly choose between courting a mate or escaping a predator? Where and how is this conflicting information evaluated in the brain to drive an appropriate action?

Using a novel behavioural assay in the fruit fly, we aim to identify neurons in the brain that allow the animal to choose between courting and escaping a threat, investigate how these neurons are connected with each other, and how they work together to select an action.

By studying how the brain selects actions at a cellular and neural circuit level, in an accessible experimental system, we aim to reveal fundamental mechanisms underlying action-selection that might be common to all animal species. This knowledge, in turn, can be exploited to better understand the complex inner workings of our own brain in health and disease.

How the brain resolves conflicting situations is a fascinating question that remains unanswered. We do not know yet how alternative options are represented in the brain, how specific actions get prioritised, and how these processes are affected in neuropathologies, such as Parkinson's disease and Alzheimer's disease. I have created an assay in which Drosophila males are presented with visual threats during courtship, which creates a conflict between reproduction and survival. Capitalising on refined genetic tools, this assay offers a great opportunity to study the neural mechanisms that govern the selection between competing options. Preliminary data shows that P1 cells are strong candidates mediating the choice between courting and escaping a threat. We will carry out a targeted behavioural screen to identify the inputs to this neural population. From an in silico screen of 3500 Gal4 fly lines targeting defined cells, I have selected 40 lines based on their potential connectivity with P1 cells. Using optogenetics, we will identify cells that, when activated or silenced with light pulses, prevent males from blocking courtship in response to the threat. We will also test 40 Gal4s that label neuromodulatory cells likely interacting with P1 cells. Next, we will ask if candidate cells respond to the threat in live imaging studies using Ca2+ indicators, and test if they are linked with the courtship circuitry using pre and post-synaptic markers and sybGRASP (to test potential synaptic connections). To probe if candidate neurons are functionally linked, we will optogenetically manipulate the activity of upstream cells, and monitor the responses in downstream cells with Ca2+ imaging. This will allow us to build a map of the neural network of action-selection. Finally, we will test how external factors and internal state variables modulate action-selection. This study will provide insights into fundamental brain processes that may work in other animals, including humans.

Selecting the most appropriate action under conflicting circumstances is essential for an individual's fitness and survival. The mechanisms underlying evaluation and appropriate action-selection in the brain remain unknown. Our research in the genetically tractable organism Drosophila seeks to understand the mechanisms that govern the selection between competing options. This research will help us better understand fundamental brain mechanisms that might be present across species, including humans.

How might individuals, organisations or society benefit from this research?

Scientific community: Fruit fly research has greatly contributed to the field of neuroscience, allowing breakthrough discoveries in nervous system development and function. In particular, Drosophila has emerged as both an interesting and tractable model to study brain computational tasks. This is due to the availability of sophisticated genetic tools that permit precise manipulation of neural activity in the fruit fly, a numerically reduced nervous system of ~100,000 neurons (compared to ~1000x as many in mice), and the design of methods to quantitatively characterise complex behaviours. Given that different animal species might share basic mechanisms for dealing with behavioural choices, this research is likely to lead to discoveries that will not only impact invertebrate neuroscience but will also guide research efforts in vertebrate models.

The BBSRC will benefit from the creation of internationally competitive research in neurobiology; this project addresses questions that are important globally, such as how the brain optimises action-selection. Working with Drosophila means less use of vertebrate models, saving on housing and husbandry costs as well as ethical considerations. This has long been a goal of the UK Research Councils and of society at large and falls under the aims of the 3Rs programme: replacement, reduction and refinement.

The society will benefit from new knowledge and scientific advancement resulting from this project. Although this project is in basic biology, it will result in discoveries that might have important longer-term implications for understanding the brain, and treatment of diseases of the nervous system, such as addiction and neurological disorders (e.g., Alzheimer's disease and Parkinson's disease). In addition, studies that contribute to our knowledge of reproductive behaviours in Drosophila are particularly important to other dipteran insects of medical importance, for instance, mosquitoes. Discoveries generated on mechanisms of mating suppression in the fruit fly might help the development of new or more effective ways of controlling insect pests or disease vectors. The society will also benefit from the creation of highly skilled researchers as a result of training in this project.

Students, research staff and general public: We will communicate how and why we use model organisms to study basic mechanisms that might be common to all animal species. This proposal will generate exciting experimental paradigms for teaching school children and undergraduates alike. The general public will benefit by attending our annual public research events at the University of Birmingham. We will advertise our work via our lab webpage, social media, and the University's website. We will work alongside the University Press Office to facilitate media publicity. Our findings will be disseminated in presentations at conferences and research articles in Open Access journals. Staff employed to work on this project will receive scientific training in many specialist techniques. In addition, we will offer internships for international visitors, College and undergraduate summer students, enabling them to get training in several laboratory techniques.