- Type 1 dopamine neurons decrease dopamine after failing to get an expected reward leading to feeling down.
- Type 2 dopamine neurons increase dopamine after disappointing outcomes and promote trying again.
- The ability to cope with the absence of expected rewards is essential for motivation and resilience.
The intricate workings of the dopaminergic system hold the key to understanding the neural underpinnings of various psychiatric conditions. Pathologies within this system have been closely linked to depression, attention deficit disorder, anxiety, and cognitive disorders. The use of specific medications to manage symptoms associated with these conditions highlights the crucial role of dopamine in their treatment. While medications for anxiety, depression, ADHD, and Parkinson's disease boost dopamine levels, antipsychotics work by reducing dopamine activity. Moreover, optimal dopamine levels have been shown to enhance learning, memory, and attention.
Beyond its involvement in psychiatric disorders, dopamine has long been associated with processes related to pleasure, reward, and motivation. A dedicated circuit within the brain is responsible for processing reward, with its origins found in the midbrain dopamine factory. One particular firing signature within this circuit, known as reward prediction error (RPE), plays a critical role in learning based on reward value (1). RPE neurons are instrumental in computing the discrepancy between expected and received rewards. When we engage in rewarding activities, our brains release a surge of dopamine, resulting in a pleasurable sensation. Consequently, we learn to seek out behaviors that trigger this dopamine surge. Furthermore, when the reward exceeds our expectations, the brain generates a positive RPE, leading to an amplified release of dopamine. Conversely, when we anticipate a reward that does not materialize, the brain generates a negative RPE, causing a decrease in dopamine release.
However, a curious question arises: If our dopamine levels dip after experiencing the disappointment of an unmet reward expectation, how do we find the motivation to try again? Consider the scenario of working for hours on a proposal, article, or project, only to receive a rejection upon submission. Is there a mechanism that propels us to pursue future rewards after such failure? Do some individuals exhibit greater resilience in the face of failure than others? What sets apart those who quickly rebound and try again from those who dwell in failure for days? Researchers at Kyoto University's Graduate School of Medicine have recently made an intriguing discovery regarding the dopaminergic neurons in rats, shedding light on these questions. They have coined the term "anti-RPE" to describe this set of dopaminergic neurons that support persistence after experiencing disappointment (2).
To recapitulate, RPE neurons respond to rewards by increasing dopamine release, while the disappointment, sadness, and frustration stemming from the rejection of our projects can be attributed to the dip in dopamine levels. In contrast, the newly identified anti-RPE neurons exhibit the opposite response pattern. Surprisingly, anti-RPE neurons decrease firing and dopamine release in response to unexpected rewards, but increase dopamine release when faced with an unanticipated reward omission. If you have poured your efforts into a project, felt confident about its quality, and then experienced rejection, you would undoubtedly feel disappointment. Paradoxically, this disappointment activates the anti-RPE neurons, leading to an increase in dopamine levels. The researchers refer to these neurons as type 2 dopamine neurons to distinguish them from the traditional type 1 dopamine neurons.
This apparent fluctuation of dopamine levels, both increasing and decreasing in response to reward absence, prompts a fascinating inquiry: How does the brain reconcile seemingly opposing error signals? Which signal should the brain prioritize—disappointment or the motivation to try again? These two types of signals occur sequentially, with type 2 neurons operating on a slower time scale compared to type 1 neurons. Consequently, the opposite signals do not cancel each other out due to their distinct time dynamics. This intricate and coordinated interplay between type 1 and type 2 neurons enables adaptive and robust pursuit of uncertain rewards. The sequential and complementary roles of RPE and anti-RPE signaling errors provide the foundation for learning from reward value and actively processing reward omission to facilitate future attempts following failures. The researchers employed innovative techniques to establish a causal relationship, suggesting that type 2 dopamine activity is "likely causally related to behavioral adjustment in coping with the absence of expected rewards." Type 2 dopamine signaling thus underlies an active approach to coping with unexpected failures.
Inability to adjust to the absence of expected rewards can result in depressive states, diminished productivity, helplessness, and hopelessness. We must not abandon the pursuit of rewards after failing to attain earlier ones. The ability to cope with the lack of expected rewards is crucial for pursuing uncertain rewards and, ultimately, obtaining more significant achievements. A short latency in trying again after errors and embracing failure serves as a prerequisite for initiating innovative projects. The type 2 dopamine error signal assumes a critical role in situations that demand new learning and behavioral adjustments, especially when error rates are high.
The most successful individuals swiftly rise after stumbling, brushing off setbacks and forging ahead. In contrast, some individuals ruminate over their failures for hours or even days before considering another attempt. The time it takes for individuals to try again after experiencing disappointment varies, highlighting individual differences in coping mechanisms. Researchers at Kyoto University have uncovered a robust correlation between type 2 dopamine neurons and the latency to attempt the next trial in rats. The stronger the type 2 responses following a failed attempt to obtain a reward, the shorter the delay in making another attempt to attain future rewards. Astonishingly, failure serves as a catalyst for renewed efforts toward success. The presence of dopamine motivates us to try again quickly in our pursuit of success after encountering failure. Individuals who dwell on their failures inadvertently delay the biological response that supports their potential for future success.
In conclusion, the intricate mechanisms of the dopaminergic system provide valuable insights into the realms of motivation and coping with failure. Understanding how dopamine influences reward processing, disappointment, and the subsequent motivation to persist can profoundly impact our lives. Deficiencies in the ability to adapt to the absence of expected rewards can lead to detrimental consequences such as depressive states, reduced productivity, and a sense of helplessness. To achieve success and pursue uncertain rewards, we must embrace failure, learn from it, and promptly resume our journey. The type 2 dopamine error signal emerges as a critical determinant, driving active coping with unexpected failures rather than succumbing to passivity. By leveraging this knowledge, we can cultivate resilience and propel ourselves toward greater achievements. Learn strategies to implement these findings in this article.
(1) W. Schultz, P. Dayan, P. R. Montague, A neural substrate of prediction and reward. (1997), Science
(2) Ishino, S., Kamada, T., Sarpong, G. A., Kitano, J., Tsukasa, R., Mukohira, H., Sun, F., Li, Y., Kobayashi, K., Naoki, H., Oishi, N., & Ogawa, M. (2023). Dopamine error signal to actively cope with lack of expected reward. Sci. Adv., 9(eade5420).