[]Title:?Dopamine error signal to actively cope with lack of expected reward

[]Journal/Year:?Sci. Adv.? (2023)

[]DOI:?10.1126/sciadv.ade5420

[]Key Findings: by training rats to perform an operant conditioning task, the authors found that half of the recorded dopamine (DA) neurons, entitled the type-2 DA neurons, had an opposite activity pattern comparing to that of the typical reward prediction error (RPE) DA neurons. That is, the type-2 DA neurons increased their activity after the unexpected reward omission while decreased their activity after the unexpected reward. The authors proposed that the type-2 DA neurons signal the unexpected reward omission, which might drive animals actively?to keep pursuing reward?even facing a negative feedback. And this response pattern can be termed as 'persistent' behavior.

[]Conclusion: type-2 DA neurons in the mid-brain may help animals to keep seeking reward even confronting an unexpected failed result.?

[]Comments: in this study, limited by the current techniques, it's impossible for the authors to draw a solid conclusion. However, we should appreciate the hard work from the authors, who tried their best to build a strong relationship between the type-2 DA neurons and the so-called 'persistent' behavior.?

In the DA or the reward-learning fields, the?prevalent theory of DA neurons' function is the RPE hypothesis. In scientific research and, in our daily life also, thinking out of the box is very challenging, especially when an old idea sink in the deep mind of everyone. In this sense, the authors had done a good work. Because they 'successfully' proposed a novel theory concerning the function of DA neurons.

It's a common situation in scientific research: no suitable tools are available. Then what should we do? Specifically in this study, at the present time no tools are available to directly manipulate the type-2 DA neurons (because it's defined by the activity pattern, not by the genetic markers). So it's impossible to establish a causal role of type-2 DA neurons in 'persistent' behavior. To?corroborate their hypothesis, the authors designed multiple experimental situations to specifically test the correlations between type-2 DA neurons and the active behavioral responses of animals after facing an unexpected reward omission. And consistently they observed a positive correlation. So although the direct evidence is still lacking, the multiple lines of indirect evidence earns the credits for their hypothesis. The authors shown their great endeavor. So I buy it.

[]Writing Date: 2023-04-06