The secret of motivation
Success doesn't happen by chance: If you want to achieve your goal, you need stamina. But where does the motivation for this come from? We have identified the neuronal circuit in the brain of fruit flies that drives them to peak performance in their search for food.
How neural circuits drive hungry individuals to peak performance
The scent of vinegar or fruit makes fruit flies run faster. To reach the food, they run until exhaustion. But despite the effort, they don't get any closer to their goal: The tiny flies in the lab at TUM's Weihenstephan Science Center are fixed to their upper bodies and can only run on the spot.
The movements of their legs turn a ball that floats on a cushion of air. From the speed of rotation, neurobiologist Prof. Ilona C. Grunwald Kadow can deduce how hard a fruit fly is trying to find food.
"Our experiments show that hungry individuals keep increasing their output - they run up to nine meters in a minute. Satiated fruit flies, on the other hand, give up quickly," the researcher reports. "This proves that even simple organisms show stamina and perseverance - until now, these traits were thought to be reserved for humans and other higher creatures."
A neural circuit controls stamina
Together with Julijana Gjorgjieva, Professor of Computational Neuroscience at the Technical University of Munich and an international and interdisciplinary team of researchers, Grunwald Kadow was able to identify for the first time a neuronal circuit in the brain of the small flies that controls this kind of perseverance.
That the scientists studied the motivation of fruit flies, of all things, is no coincidence. "Fly brains have a million times fewer neurons than human brains. It is therefore much easier to find out in fruit flies what a single neuron does and how," the professor explains. "This allows us to understand the principles of neural circuits that underlie the function of even complex brains."
The power of neurons
To identify the neural circuit responsible for motivation, the team used various techniques: First, they created a mathematical model that simulates the interaction of external and internal stimuli - for example, the smell of food and hunger.
In the next step, the TUM neuroscientists, together with colleagues in the USA and Great Britain, identified the network they were looking for in the fruit fly's brain. This was achieved with the help of electron microscopy, in vivo imaging and behavioral experiments.
The result: The neuronal circuit we were looking for is located in the learning and memory center of the fly's brain. It is controlled by the two neurotransmitters dopamine and octopamine. Dopamine increases the activity of the circuit, i.e. boosts motivation, while octopamine reduces the willingness to exert oneself.
"Since these messenger substances and corresponding circuits also exist in the brains of mammals, we assume that similar mechanisms decide whether to continue or stop here," summarizes the neurobiologist. In the long term, the researchers hope that their findings will help to understand why the interplay of neurons and messenger substances in the brain gets out of hand, for example, in addictive diseases.
Further information
Scientists from the TUM School of Life Sciences, the Max Planck Institute of Neurobiology, the Max Planck Institute for Brain Research, the University of Cambridge (UK), the Janelia Research Campus (USA) and the MRC Laboratory of Molecular Biology (UK) collaborated to identify neuronal circuits.
The research was supported by the Max Planck Society, the European Research Council (ERC), the Marie Curie Training Network, the German Research Foundation (DFG), the Howard Hughes Medical Institute (USA), and the Medical Research Council (UK). Julijana Gjorgjieva is a tenure track professor in the Max Planck@TUM program at the Technical University of Munich.
A Neural Circuit Arbitrates between Persistence and Withdrawal in Hungry Drosophila
Sercan Sayin, Jean-Francois De Backer, K.P. Siju, Marina E. Wosniack,Laurence P. Lewis, Lisa-Marie Frisch,Benedikt Gansen, Philipp Schlegel, Amelia Edmondson-Stait, Nadiya Sharifi, Corey B. Fisher, Steven A. Calle-Schuler, J. Scott Lauritzen, Davi D. Bock, Marta Costa, Gregory S.X.E. Jefferis, Julijana Gjorgjieva, Ilona C. Grunwald Kadow
Neuron 104, 1–15, November 6, 2019 – DOI: 10.1016/j.neuron.2019.07.028