Happiness hormone dopamine also controls fear memory
Fear and happiness seem as contradictory as day and night. Nevertheless, researchers recently found out in a study that the hormone dopamine, which was previously only known to cause happiness, also makes menacing events in the brain more memorable.
The research team included scientists from Otto von Guericke University Magdeburg and neurobiologists from the Research Institute for Molecular Pathology (IMP) in Vienna. The happiness hormone dopamine has so far been seen primarily as a mediator of reward and motivation in the brain. The scientists have now found that it also plays an essential role in storing threatening events. The results of the study were recently published in the journal "Nature Neuroscience".
Fear as a survival strategy
As an important emotion, fear and fear have ensured the survival of humanity and that of many animals. Exactly how fear arises is still not sufficiently understood. The researchers in the latest study have now come one step closer to deciphering the puzzle. It is vital for humans and animals to memorize threatening events so that they do not repeat themselves if possible. The area responsible for this is fear memory.
Memories of fear and terror
Fear memories store smells or noises that we associate with the recurrence of dangerous situations. For example, the sounds of an approaching fight or the smell of poisonous food. In this way we can react appropriately to the situation in order to avoid the danger or to prepare for it.
Happiness and fear go hand in hand
For humans, the distinction between dangerous and harmless environmental signals is an essential part of survival. The team led by neurobiologist Dr. Wulf Haubensak looked into the question of which physical processes help us to build up and recall this fear memory. It is the happiness and motivation hormone dopamine that seems to play a central role in these processes.
A new class of dopamine neurons has been discovered
The scientists gained their knowledge from experiments on mice. They played a certain tone as a stimulus to the environment. Afterwards they received a mild electric shock in the foot. Using the latest high-tech methods, the scientists were able to monitor the mouse brains and identified a new class of dopamine neurons in the midbrain region. This was activated whenever the mice learned to store the connection between sound and foot shock in their fear memory.
The activation of the neurons also released dopamine in the brain. And exactly where the center for emotional learning is located in the mammalian brain, the so-called amygdala. According to the researchers, this led to a particularly effective storage of the sound that was now perceived as threatening in long-term memory. The fact that dopamine is much more than just the messenger of happiness has already been recognized in previous studies. So far, however, these functions have been new medical ground.
Dopamine even more important than previously thought
"These results shed new light on dopamine neurons that were previously only seen as a signal for reward and motivation," explains Dr. Florian Grössl, the first author of the publication, in a press release on the study results. The study identified a previously unknown neural network, consisting of dopamine neurons and amygdala nerve cells, which is essential for the evaluation of emotions. According to Grössl, dopamine filters out the vital stimuli for the environment and stores them in the memory.
From mice to humans?
The researchers report that dopamine neurons in humans are connected to the amygdala in the same way as in mice. The scientists firmly believe that dopamine also controls these processes in humans. This could be a groundbreaking finding for the treatment of mental disorders such as post-traumatic stress disorder or pathological anxiety. Future studies are now to show whether treatment with dopamine-like drugs is suitable as a therapy for such diseases. (vb)