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Portuguese scientists highlight that these two groups of neurons tend to work together when faced with good or bad stimuli.
O brain encodes what is good and bad. And, until now, we thought of two groups of neurons, the D1 e D2, they worked as rivals in this process.
A team from the University of Minho discovered the opposite: that they tend to work together in the face of good or bad stimuli.
The recent helps to better understand the reward systemwhich is dysfunctional in illnesses such as depression and substance dependence.
In partnership with Columbia University and the Allen Institute (USA), the study was led by Ana João Rodrigues and Carina Cunha, at the Institute for Research in Life and Health Sciences (ICVS) at the UMinho School of Medicine.
D1 and D2 neurons are located in the nucleus accumbensinside the brain, which presents changes in some neuropsychiatric conditions.
These neurons are part of the reward circuit, essential in the survival of species, such as when we strive for what we need and want, from food, music or sex.
The UMinho team had already proven in mice that D1 and D2 are necessarily rivals to process negative and positive stimuli, as D2 also process positive or pleasure stimuli.
This time, says a statement sent to ZAP, scientists were more thorough and used miniaturized microscopes to track hundreds of these neurons in real time in rodents exposed to appetitive and aversive stimuli.
It was demonstrated for the first time that D1 and D2 responded together to both stimuli.
Next, we sought to understand how these neurons responded during the learning of positive and negative associations, similar to the scientist’s famous experiment Ivan Pavlov who conditioned dogs to salivate for food as soon as they heard a bell.
In this case, scientists trained the animals to associate one seam specific with the delivery of a reward or an aversive stimulus.
And the investigators were surprised upon seeing that the D1 and D2 reacted in a similar way throughout learningnot drastically changing response rates.
Quick adaptation
However, researchers changed the rules of the game: the sound was no longer accompanied by a reward or aversive stimulus.
With a nanometric precision laser that “turns on and off” specific neurons (optogenetics), scientists showed that D2 were fundamental in adapting to change. That is, when they inhibited D2 neurons, the animals took longer to “understand the new rules of the game.”
Unraveling how the brain codes and responds to external cues that predict something positive or aversive is crucial to better understanding diseases like post-traumatic stress or depression.
The same external cue can trigger very different responses depending on the individual’s context and associated memories.
For example, the sound of fireworks it refers to festive and fun moments, but for a former soldier it can generate an anxious crisis, remembering the war, even if he is in a safe environment.
The next phase of the project will try to find genetic markers that identify neurons that encode something positive and aversive, to understand what distinguishes these subtypes of neurons.
