What happens to the dopamine system when we experience aversive events?
Abstract: The dopamine system helps the brain to predict the occurrence and duration of unpleasant events, but without taking into account mistakes.
Source: Netherlands Institute for Neuroscience
A new study at the Netherlands Institute for Neuroscience examined how the dopamine system processes aversive unpleasant events.
It is well known that the dopamine system plays a key 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 dopamine system informs our brain about so-called “reward prediction errors” – the difference between received and predicted rewards.
Dopamine neurons become more active when the reward appears unexpectedly or if it is greater than expected, and show reduced activity when we receive a smaller reward than expected. These error signals help us learn from our own mistakes and teach us how to achieve rewarding experiences.
Rewarding versus aversive stimuli
While a large number of studies have focused on the relationship between dopamine release and rewarding stimuli, few have examined the effect of unpleasant and aversive stimuli on dopamine. Although the results of these few experiments are inconsistent, it has become clear that aversive stimuli affect the dopamine system.
But there is an active debate among neuroscientists about what exact role dopamine neurons play in processing aversive stimuli: does their activity change in response to aversive events? Do they predict unpleasant events? Do they encode an aversive prediction error?
New findings on the role of dopamine in aversive events
Now published in eLife, a new study at the Netherlands Institute for Neuroscience examined how the dopamine system processes aversive events. The team around Ph.D. student Jessica Goedhoop and group leader Ingo Willuhn exposed rats to white noise combined with stimuli that predicted white noise, while measuring 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 during exposure to white noise. Furthermore, after consistent presentation, stimuli that appeared a few seconds before exposure to white noise began to have the same depressant effect on dopamine neurons. However, unlike how it processes rewards, dopamine did not encode a prediction error for this aversive stimulus.
Overall, this new study shows that the dopamine system helps the brain predict the occurrence and duration of unpleasant events, but without accounting for prediction errors.
Group leader Ingo Willuhn said: “This is a very thorough and systematic study that takes many variables into account. The results give us a better understanding of the role of dopamine release in the processing of aversive events. There is increasing interest in the role of dopamine in aversion. We used a new aversive stimulus that allowed us to perform a more thorough analysis of dopamine than was previously possible.”
Addictive drugs hijack and amplify dopamine signals and cause exaggerated, uncontrolled effects of dopamine on neuronal plasticity. This study brings us closer to understanding the underlying mechanism behind this pathological phenomenon.
About this dopamine research news
Original research: Open access.
“Nucleus accumbens dopamine monitors aversive stimulus duration and prediction, but not value or prediction error” by Jessica N Goedhoop et al. eLife
Nucleus accumbens dopamine monitors aversive stimulus duration and prediction, but not value or prediction error
There is active debate about the role of dopamine in the processing of aversive stimuli, with hypothesized roles ranging from no involvement to signaling an aversive prediction error (APE).
Here, we systematically investigate dopamine release in the nucleus accumbens (NAC), which is closely related to reward prediction errors, in rats exposed to white noise (WN, versatile, underutilized, aversive stimulus) and its predictive cues.
Both induced a negative dopamine ramp, followed by slow signal recovery after stimulus termination. Unlike reward conditioning, this dopamine signal was unaffected by WN value, context valence, or probabilistic contingencies, and the WN dopamine response only partially shifted toward its predictive cue.
However, the unpredicted WN elicited a slower recovery of the post-stimulus signal than the predicted WN. Despite the different qualities of the signals, the dopamine responses to the simultaneous presentation of rewarding and aversive stimuli were additive.
Together, our findings indicate that rather than APE, NAC dopamine preferentially accompanies the anticipation and duration of aversive events.