Summary: The dopaminergic system helps the brain to anticipate the occurrence and duration of unpleasant events, but without taking errors into account.
Source: Netherlands Institute for Neuroscience
A new study from the Netherlands Institute for Neuroscience examined how the dopaminergic system processes aversive unpleasant events.
It is well known that the dopaminergic system plays a crucial role in motivation, learning and movement. One of the main functions of dopamine is to predict the occurrence of rewarding experiences and the availability of rewards in our environment. In this context, the dopaminergic system informs our brain about so-called “reward prediction errors” – the difference between received and expected rewards.
Dopamine neurons become more active when a reward occurs unexpectedly or if it is greater than expected, and they show depressed activity when we receive less of a reward than expected. These error signals help us learn from our mistakes and teach us to have rewarding experiences.
Rewarding stimuli versus aversive stimuli
While a large number of studies have focused on the relationship between dopamine release and reward stimuli, few have looked at the effect of unpleasant and aversive stimuli on dopamine. Although the results of these few experiments were inconsistent, it became clear that aversive stimuli have an impact on the dopaminergic system.
But there is an active debate among neuroscientists about the precise role that dopamine neurons play in processing aversive stimuli: does their activity change in response to aversive events? Do they predict aversive events? Do they encode aversive prediction error?
New findings on the role of dopamine in aversive events
Now published in eLife, a new study from the Netherlands Institute for Neuroscience examined how the dopaminergic system processes aversive events. The team around Ph.D. student Jessica Goedhoop and group leader Ingo Willuhn exposed rats to white noise in combination with stimuli that predicted white noise, as they measured dopamine release in the brain. White noise is a well-known example of an unpleasant auditory stimulus for rats.
The researchers found that dopamine release gradually decreased upon exposure to white noise. Moreover, after coherent presentation, stimuli that occurred seconds before white noise exposure began to have the same depressant effect on dopaminergic neurons. However, unlike how it processes rewards, dopamine did not encode prediction error for this aversive stimulus.
Overall, this new study demonstrates that the dopaminergic system helps the brain anticipate the occurrence and duration of unpleasant events, but without taking into account prediction errors.
Group leader Ingo Willuhn said: “This is a very thorough and systematic study that takes into account many variables. The results allow us to better understand the role of dopamine release in the processing of aversive events. There is growing interest in the role of dopamine in aversion. We used a new aversive stimulus that allowed for deeper analysis of dopamine than before.
Addictive drugs hijack and amplify dopamine signals and induce exaggerated and uncontrolled dopaminergic effects on neuronal plasticity. This study brings us closer to understanding the mechanism underlying this pathological phenomenon.
About This Dopamine Research News
Author: Press office
Source: Netherlands Institute for Neuroscience
Contact: Press Office – Netherlands Institute for Neuroscience
Image: Image is in public domain
Original research: Free access.
“Nuclear accumbens dopamine tracks aversive stimulus duration and prediction, but not value or prediction error” by Jessica N Goedhoop et al. eLife
Nucleus accumbens dopamine tracks aversive stimulus duration and prediction, but not value or prediction error
There is active debate about the role of dopamine in processing aversive stimuli, where inferred roles range from no involvement at all to signaling aversive prediction error (APE).
Here, we systematically investigate the release of dopamine in the nucleus accumbens (NAC), which is closely related to reward prediction errors, in rats exposed to white noise (WN, a versatile, underutilized and aversive stimulus) and its predictive signals.
Both induced a negative dopamine ramp, followed by slow signal recovery upon stimulus cessation. Unlike reward conditioning, this dopamine signal was unaffected by WN value, contextual valence, or probabilistic contingencies, and the WN dopamine response shifted only partially toward its predictive signal.
However, the unpredicted WN caused slower post-stimulus signal recovery than the predicted WN. Despite differing signal qualities, dopamine responses to the simultaneous presentation of gratifying and aversive stimuli were additive.
Together, our results demonstrate that instead of an APE, dopamine NAC primarily tracks the prediction and duration of aversive events.
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