Making balanced decisions
How decisions are made and behavior is controlled is one of the most important questions in neuroscience. The neurotransmitter dopamine plays an essential role in our brain. We study the functions of dopamine in decision-making and in the control of movement.
Scent and taste preferences are innate
Living things have an innate preference for scent and taste. Attractive scents, for example, are linked to food. In the case of less attractive scents - for example, spoiled food - a living being instinctively knows: "There could be danger here!" All creatures also have similar preferences when it comes to taste: Sugar and fats are perceived positively, a bitter taste rather negatively.
In order to make such evaluations, we need signals in the brain that tell us, "This is good!" or, "This is bad!" An important role in these evaluations is played by the dopaminergic system in the brain, better known as the reward system.
Understanding processes in the brain
Neurons that signal through dopamine/produce dopamine, so-called dopaminergic neurons, are relevant for many diseases. Addictive behavior, obesity or even Parkinson's disease are examples. In addiction or obesity, the reward system goes haywire; in Parkinson's, dopaminergic neurons die and affect motor control.
To learn more about the processes in the brain, basic research is indispensable. Ilona Grunwald Kadow, Professor of Neuronal Control of Metabolism at the TUM School of Life Sciences at the Weihenstephan site, along with her team, are conducting research on the fly Drosophila melanogaster.
Neuroscientists often use this fly as a model for their research because its neuronal networks are much simpler than those of humans and genetic tricks allow the role of individual network components to be switched on and off or changed in a targeted manner. This allows researchers to understand the principles of neuronal circuits underlying the function of even more complex brains. For example, dopamine plays a very similar role in the brains of humans and insects.
Further elucidating the effect of dopamine
Dopamine is among the most intensively studied signals in the brain. It is involved in both cognitive (e.g., motivation, reinforcement, goal-directed behavior, motor control and movement, decision making, and learning) and more basic functions (e.g., reproduction and nausea).
How dopamine contributes to different aspects of neural circuit function and behavior is an open question, but it is thought that dopaminergic neurons signal to the brain what the organism needs and feels through different patterns of activity. "We have now studied the activity of dopaminergic neurons in more detail," says Ilona Grunwald Kadow. The team developed a new 3D imaging method specifically for this purpose based on in vivo calcium imaging, since 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 joint activity of a network of dopaminergic neurons reflects both the innate smell or taste preferences and the physiological state of the organism.
In addition to sensory stimuli such as odors or tastes, dopaminergic neurons also pick up information about whether or not a creature is in motion. The neurons can respond to and combine internal behavioral states and external signals to support both cognitive and motor processes.
"In doing so, the neurons can respond flexibly and individually to the most important information - such as scent, taste, but also hunger or one's own movement. This is important for a balanced decision, because an external signal can sometimes mean good or sometimes bad, depending on the state," says Prof. Grunwald Kadow.
Surprising results
The researchers were surprised to find that dopaminergic neurons behave quite differently from animal to animal. The scientists speculate that this may explain differences in individual preferences and behavior. In addition, it was shown that the movement of the animal not only activates these dopaminergic neurons, but also other areas of the brain that actually have nothing to do with movement per se. This provides starting points for further research, for example on the role that movement plays in general brain activity.