The mechanism by which dopamine cells in the brain signal the passage of time has received some new light via a recent study from researchers at University of Texas at San Antonio. To make decisions about the salience of a potential reward is mediated by small group of neurons in the midbrain that release dopamine.

The amount of dopamine released can influence our decisions by telling us how good a reward will be in the future. For example, more dopamine is released in response to the smell of turkey baking relative to the smell of leftovers.

But does the length of time between the anticipatory release of dopamine and the actual reward mediate the release and volume of dopamine? To answer this question, investigators used voltammetry to record dopamine release in rodents trained by Pavlovian conditioning.

This novel experiment utilized different audible tones that predicted the delivery of food. One tone was presented only after a short wait time— while the other tone was presented only after a long wait time.

The data showed that more dopamine was released during the short wait tone compared to the long wait tone. These results show that imminent reward is associated with dopamine release in the midbrain.

This is not unlike telling a 6-year-old child that her next birthday party is tomorrow versus telling her it won’t occur for two months. The time differentiation will predict the amount of excitement the child experiences.

Why Does This Matter?

We established many years ago the power of simply showing a recovering cocaine addict a piece of their drug paraphernalia. The release of dopamine is triggered by this visual cue and is also related to the amount of abstinence and how soon a drug reward could be attained. Monitoring via drug testing is one way that addicts are able to think through their behavioral choices when craving is induced.

For persons in early recovery from substance use disorder, anticipatory cues trigger the release of dopamine, cause craving and increase the risk of relapse. Continuing care planning for recovering addicts must address the power of anticipatory reward and help each recovery person set up obstacles that deter and delay access to a mood altering substance and avoid environmental drug cues.

Source: Fonzi KM, Lefner MJ, Phillips PEM, Wanat MJ. Dopamine Encodes Retrospective Temporal Information in a Context-Independent Manner. Cell Rep. 2017 Aug 22;20(8):1765-1774. doi: 10.1016/j.celrep.2017.07.076.