We all know the feeling of anticipation associated with waiting to eat. Regardless of how hungry you are, patience levels tend to fluctuate based on the circumstances and your degree of that you'll have some food close to the time you expected to eat. For example, if the wait time at a restaurant becomes much longer than expected, most of us will become impatient. But, if we are highly confident that we'll be seated and eating close to the time of our dinner reservation, our patience will be higher and we'll gladly wait a bit longer.

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McDonald’s recently struggled with “the patience effect” after introducing a cooked-to-order Quarter Pounder made with fresh beef, which takes one minute longer to cook than a frozen patty. Initially, drive-thru customers were irate about their unexpected delay in gratification. Because customers in test markets didn’t know they were guinea pigs for the new fresh beef patties, the extra 60-second wait time at a fast-food restaurant was unexpected and patience quickly wore thin. However, once customers knew that their Quarter Pounders were now being cooked to order and that there was a reason for the delay, confidence in receiving food when expected and patience grew in tandem.

As another example of marketers realizing the need to remind consumers to be patient when waiting to eat: In the 1970s, Heinz ketchup was still being sold in glass bottles. Unlike the instant gratification of today's upside-down plastic squeeze bottles, the old glass bottles took some shaking, artful tapping, and patience before the ketchup would slowly ooze through the narrow opening at the top of the bottle. Madison Avenue ad executives realized the need to keep customers happy by making unavoidable "ketchup wait time" something that consumers should expect without becoming disgruntled.

Brilliantly, the H.J. Heinz company licensed Carly Simon's top 40 hit, "Anticipation," and created the tagline "It's Slow Good" to increase consumers' subjective confidence that the ketchup would eventually dispense, but that it would take a few seconds. Knowing that the thickness of the ketchup was linked to higher quality made people more patient and less irritated by their delayed gratification.

Mice in a lab aren’t much different than humans waiting at the drive-thru or for ketchup to dispense from an old glass bottle. In a recent experiment, researchers pinpointed the role that serotonin plays in “the patience effect” depending on the confidence a mouse has that it’s worth waiting a few extra seconds for a delayed food reward. The new study, “Reward Probability and Timing Uncertainty Alter the Effect of Dorsal Raphe Serotonin Neurons on Patience,” was published June 1 in the journal Nature Communications. This research was conducted by Katsuhiko Miyazaki and colleagues in the Computation Unit at the Okinawa Institute of Science and Technology Graduate University (OIST).

Previous research on “the patience effect” while waiting for future rewards used optogenetic activation of serotonin neurons in the dorsal raphe nucleus (DRN) to identify a link between serotonergic activity and patience. Boosting serotonin activity in the DRN significantly increased the amount of time mice would wait for a food reward.

The central research question for the new study by Miyazaki et al. was, “Would mice wait for food regardless of the probability and timing of it turning up, or would they give up if they predicted a low chance of return on their time investment?”

Source: Courtesy of OIST

As the diagram above illustrates, the researchers found that stimulating serotonin production made the mice willing to wait for a food reward if they knew there was at least a 75% chance of being fed after waiting a maximum of 10 seconds. When the odds of receiving the food reward slipped below this threshold, serotonin failed to increase patience. "The patience effect only works when the mouse thinks there is a high probability of reward," Miyazaki said in a statement.

The main takeaway from this research is that the link between serotonin levels and subsequent behavior appears to be highly dependent on a mouse's subjective confidence in an expected outcome. Although this research was on mice, the authors speculate that there may be human implications that can help us better understand various ways to optimize the efficacy of serotonin-boosting pharmaceuticals such as Selective Serotonin Receptor Inhibitors ( ).

"Serotonin has had a lot of study in pharmacology, and serotonergic drugs are commonly prescribed, but the role that serotonin has over behavior isn't clear. This [study] could help explain why combined treatment of with SSRIs and Cognitive Behavior ( ) is more effective than just SSRIs alone," according to Katsuhiko Miyazaki. "The psychological boost of the therapy is enhanced by raised serotonin levels."