Summary There is active debate about the role of dopamine in processing aversive stimuli, where inferred roles range from not engaging at all to signaling an aversive prediction error (APE). Here, we systematically investigated dopamine release in the nucleus accumbens core (NAC), which is closely related to reward prediction errors, in rats exposed to white noise (WN, a versatile and underused aversive stimulus) and its predictive cues. Both induced a negative dopamine ramp, followed by a slow recovery of the signal upon cessation of the stimulus. In contrast to reward conditioning, this dopamine signal was not affected by WN value, context valence, or probabilistic contingencies, and the WN dopamine response was only partially shifted toward its predictive signal. However, the unexpected WN caused a slower recovery of the post-stimulus signal than the predicted WN. Despite the different cue qualities, dopamine responses to the simultaneous presentation of rewarding and aversive stimuli were additive. Together, our findings demonstrate that, rather than a PSA, NAC dopamine primarily tracks the prediction and duration of aversive events. Editor’s rating The article by Goedhoop et al. provides an important analysis of the role of terminal dopamine release in the nucleus accumbens in the processing of aversive events that will be valuable to researchers interested in the neural mechanisms of reinforcement learning and computational modeling of dopamine function. Using a variety of conditions, the authors provide compelling data supporting the role of accumbal dopamine release in the processing of aversive events that situate the current report amid growing interest and growing research on the role of dopamine in aversion. |
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Nucleus accumbens dopamine tracks the duration and prediction of the aversive stimulus, but not the value or prediction error
It is well known that the dopamine 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 dopamine system informs our brain about so-called "reward prediction errors" , the difference between received and predicted rewards. Dopamine neurons become more active when a reward occurs unexpectedly or if it is greater than expected, and show depressed activity when we receive less reward than expected. These error signals help us learn from our 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 analyzed the effect of unpleasant and aversive stimuli on dopamine. Although the results of these few experiments have been inconsistent, it has become clear that aversive stimuli have an impact on the dopamine system. But there is an active debate among neuroscientists about the precise role that dopaminergic neurons play in processing aversive stimuli: does their activity change in response to aversive events? Do they predict aversive events? Do they encode an aversive prediction error?
New findings on the role of dopamine in aversive events
A new study from the Netherlands Institute of Neuroscience has examined how the dopamine system processes aversive events. The team consisting of doctoral student Jessica Goedhoop and group leader Ingo Willuhn exposed rats to white noise in combination with stimuli that predicted white noise, while measuring the release of dopamine 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 occurred a few seconds before white noise exposure began to have the same depressive 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 demonstrates that the dopamine system helps the brain anticipate the occurrence and duration of unpleasant events, but without taking into account prediction errors.
Group leader Ingo Willuhn: ’This is a very complete 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 growing interest in the role of dopamine in aversion. “We used a novel aversive stimulus that allowed for a more complete analysis of dopamine than was previously possible.”
Addictive drugs hijack and amplify dopamine signals and induce exaggerated and uncontrolled dopamine effects on neuronal plasticity . This study brings us closer to understanding the underlying mechanism behind this pathological phenomenon.
