WHEN DOPAMINE IS RELEASED IN RESPONSE TO AN AVERSIVE STIMULUS, RATHER THAN A REWARDING ONE

While dopamine is known as a signal for reward (or the anticipation of a reward), some neurons that express dopamine release dopamine in response to an AVERSIVE stimulus. The authors of a very recent paper (Lloyd, 2016) pointed out that an aversive stimulus could, if there is a way to escape it, actually be a rewarding stimulus because safety can be a reward. As they point out, “...relative to this new state of danger, the possible prospect of future safety—a positive outcome—comes into play.” “Thus, provided the animal has the expectation that it will ultimately be able to achieve safety, i.e., that the situation is controllable, observation of the aversive stimulus should predict this future appetitive [rewarding] outcome...” Another paper expressed it this way: “Neural activity in a region previously implicated in encoding stimulus reward value, the medial orbitofrontal cortex, was found to increase, not only following receipt of reward, but also following successful avoidance of an aversive outcome. This neural signal may itself act as an intrinsic reward, thereby serving to reinforce actions during instrumental avoidance.” (Kim, 2006)

This leads to the interesting economic concept of “opportunity costs,” where there is a cost to NOT doing a thing that might have a large payoff. “... if the subject fails to explore, for instance because it believes the aversive stimulus to be insufficiently controllable, then it would never discover that it actually might be removed.” The researchers then go on to explain that an inadequate response by the dopamine (D2) receptor could lead to a failure to consider the possibility of achieving safety.

References

Lloyd and Dayan. Safety out of control: dopamine and defence. Behav Brain Funct. 12:15 (2016).

Kim et al. Is avoiding an aversive outcome rewarding? Neural substrates of avoidance learning in the human brain. PLoS Biol. 4(8):e233 (2006).

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