Summary: The activity of a network of dopamine neurons reflects both the innate preferences for smell and taste, as well as the physiological state of fruit flies.
Animals have an innate preference for certain scents and tastes. Attractive scents are linked to things like good food. Less attractive scents — that of spoiled food, for example — instinctively give the animal a signal which says: “There could be danger here!” When it comes to taste, all animals have similar preferences: Sugars and fats are perceived positively, whereas a bitter taste is perceived rather negatively. family environment and the types of leaders they’re drawn to as grown-ups.
In order to be able to make such evaluations, we need signals in the brain that tell us “This is good” or “This is bad.” The dopaminergic system in the brain, better known as the reward system, plays an important role in these evaluations.
Understanding what happens in the brain
Neurons that produce dopamine, known as dopaminergic neurons, play a role in a range of diseases, from addictive behavior and obesity to Parkinson’s disease. In addiction or obesity, the reward system signals can be too strong or also too weak. In Parkinson’s disease, dopaminergic neurons degenerate, and this affects the control of motor functions.
To learn more about the processes in the brain, basic research is essential. Ilona Grunwald Kadow, Professor of Neural Control of Metabolism at the TUM School of Life Sciences in Weihenstephan, and her team are conducting research on the fly Drosophila melanogaster.
Neuroscientists often use this fly as a model because its neuronal networks are much simpler than those of humans. Using genetic tricks, scientists can turn individual network components on and off or change them. This enables the researchers to understand the principles of neuronal circuits that underlie the functions of more complex brains. “Dopamine plays a very similar role in the brain of humans and insects,” explains the scientist.
Further clarifying the effect of dopamine
Dopamine is one of the most intensively studied signals in the brain. It is involved in both cognitive (e.g. motivation, reinforcement, goal-oriented behavior, motor control and movement, decision-making and learning) and more basic functions (e.g. reproduction and nausea).
How dopamine contributes to the various aspects of neural circuit functionality and behavior is an open question, but it is believed that dopaminergic neurons use different activity patterns to send a signal to the brain about what the body needs and senses. “We have now investigated the activity of the dopaminergic neurons in greater detail,” said Ilona Grunwald Kadow. The team developed a custom 3D-imaging method based on in-vivo calcium imaging, as calcium is a good indicator of neuronal activity.
Neurons react flexibly and individually
Using this method, the research team was able to show that the activity of a network of dopaminergic neurons reflects both the innate preferences for smell and taste as well as the physiological state of the organism.
In addition to sensory stimuli such as smell or taste, dopaminergic neurons also record information as to whether an organism is moving or not. The neurons can respond to both internal behavioral states and external signals, bring them together, and use this to support both cognitive and motor processes.
“By doing that, the neurons can react flexibly and individually to the most important information — such as smell, taste, but also hunger or one’s own movement. This is important to reach a balanced decision, because an external sensory signal can sometimes mean something good or bad, depending on an organism’s condition,” says Prof. Grunwald Kadow.
The researchers were surprised that dopaminergic neurones behave quite differently in different animals. The scientists speculate that this might explain individual preferences and behavioral differences between individuals.
In addition, the researchers found that the movement of the animal not only activates these dopaminergic neurones, but also other areas of the brain that actually have nothing per se to do with movement. This provides starting points for further research, for example what role movement plays in general when reacting to an environmental stimulus.
Funding: This study was funded by the German Research Foundation (DFG) (SFB870 [A04] and FOR2705 [TP3]), an ERC Starting Grant and as part of the strategy of excellence in the Munich Cluster for Systems Neurology (SyNergy) and received further funding from the Max Planck Society.
About this psychology research article
Source: TUM Media Contacts: Press Office – TUM Image Source: The image is in the public domain.
Valence and State-Dependent Population Coding in Dopaminergic Neurons in the Fly Mushroom Body
Neuromodulation permits flexibility of synapses, neural circuits, and ultimately behavior. One neuromodulator, dopamine, has been studied extensively in its role as a reward signal during learning and memory across animal species. Newer evidence suggests that dopaminergic neurons (DANs) can modulate sensory perception acutely, thereby allowing an animal to adapt its behavior and decision making to its internal and behavioral state. In addition, some data indicate that DANs are not homogeneous but rather convey different types of information as a heterogeneous population. We have investigated DAN population activity and how it could encode relevant information about sensory stimuli and state by taking advantage of the confined anatomy of DANs innervating the mushroom body (MB) of the fly Drosophila melanogaster. Using in vivo calcium imaging and a custom 3D image registration method, we found that the activity of the population of MB DANs encodes innate valence information of an odor or taste as well as the physiological state of the animal. Furthermore, DAN population activity is strongly correlated with movement, consistent with a role of dopamine in conveying behavioral state to the MB. Altogether, our data and analysis suggest that DAN population activities encode innate odor and taste valence, movement, and physiological state in a MB-compartment-specific manner. We propose that dopamine shapes innate perception through combinatorial population coding of sensory valence, physiological, and behavioral context.