Recognizing receipt of reward in others guides our daily behavior. For example, children that observe classmates receive reinforcement for good behavior recognize the benefits of such actions. In the work place, observation of colleagues receiving a promotion lets us know that our work has potential payoff. These are all positive associations that alter our own behavior based on receipt of reward in others. It is unknown what brain regions represent this information. One likely candidate is the dopamine (DA) system. We know that DA is released in ventral striatum (VS) when reward is unexpectedly delivered and is critical for reinforcement learning. It might also be critical for recognizing rewards delivered to others, yet this hypothesis has never been tested. Here, in AIM 1, we ask if subsecond DA release is elevated in rats when reward is delivered to a conspecific. However, social observation of reward does not always lead to positive affect. For example, observing your colleague get promoted or receive a bonus instead of you, might lead to jealousy, frustration, and other negative affective states. This emotion must reflect a discrepancy between the reward that you expect for yourself and what you actually received. Such signals are referred to as negative prediction errors and are encoded by midbrain DA neurons. It is unknown if this signal is modulated by observation of reward delivered to others. Here, in AIM 2, we will ask if subsecond DA release related to negative predictions errors are modulated by conspecific reward. These are not just interesting questions that would advance our basic understanding of the DA system, but they are clinically relevant because the ability to recognize reward in a conspecific is disrupted in several psychiatric disorders (e.g., autism, psychopathy). To date, we know very little about the neurobiological substrates that control these functions because detailed work in animals at the single-unit and neurotransmitter level has not yet occurred. Here we propose a first step to addressing this issue. We will record subsecond DA release using fast-scan cyclic voltammetry (FSCV) in VS, while rats observe reward delivery to a conspecific in cases when they do or do not expect reward for themselves. We will examine differences between cagemates and non-cagemates because 'empathy' studies have suggested that cagemates are more adept at recognizing social cues compared to rats that are unacquainted. If successful, these studies will lead to a host of experiments that would test observational learning and underlying circuits, but as a first step, we must determine if DA signals are necessary and sufficient for behavioral output.
The proposed research is relevant to public health because the inability to recognize reward in others is a hallmark of many psychiatric disorders. This proposal is particularly relevant to the aims of NIMH because it will substantially improve our insight into how dopamine signals are altered in animals during conspecific reward, a function that might be disrupted in humans with autism for example. A full and proper understanding of this circuitry is essential to the development of more effective treatment solutions and diagnostic strategies.
| Lichtenberg, Nina T; Lee, Brian; Kashtelyan, Vadim et al. (2018) Rat behavior and dopamine release are modulated by conspecific distress. Elife 7: |
| Kashtelyan, Vadim; Lichtenberg, Nina T; Chen, Mindy L et al. (2014) Observation of reward delivery to a conspecific modulates dopamine release in ventral striatum. Curr Biol 24:2564-8 |
