OKINAWA, Japan — In this fast-moving world of ours, we don’t always have to be patient and wait long for what we want. We can download movies to watch now and order items that will be on our doorstep by the next day. But what is it that allows us to patiently await something that we want? A recent study on mice finds that serotonin, a chemical messenger found in the nervous system, combines with confidence to increase the length of time a mouse was willing to wait for an expected reward.
The study, conducted by Dr. Katsuhiko Miyazaki and Dr. Kayoko Miyazaki at the Okinawa Institute of Science and Technology Graduate University (OIST) hoped to find out the role that serotonin has over human behavior, which isn’t clearly understood. Serotonin is involved in many aspects of behavior including mood, sleep, and cravings.
Researchers found that serotonin helped mice to stay patient when waiting for a food reward, especially when the mice weren’t sure when or if they would receive one.
A previous study found that mice will wait for a reward when they know it’s coming in a set amount of time. In that study, the mice were given food when they placed their nose in a hole, which the researchers called a “nose-poke.” The experiment showed that increasing serotonin activity in a certain part of their brain resulted in the mice patiently waiting for the food.
This more recent study was interested in finding out if the mice would continue to wait for a food reward when they didn’t know how long they would have to wait. The authors wondered whether serotonin would continue to give the mice the patience they needed.
Serotonin did increase patience, but its effect on the mice’s behavior only went so far. Increasing serotonin activity in the mice had no effect when the chance of a reward was low — around 25% or 50%. The mice waited longer when the chance of a reward was high, around 75%, even when they didn’t know how long it would take to receive that reward.
When researchers reviewed their data they found that a 75% chance of reward prompted the same behavior as a 95% chance and the mice behaved like they were certain they would receive food.
The results of this study may have some implications for human behavior. Drugs that affect serotonin activity in humans are used for treating depression. These drugs are known as SSRIs, or selective serotonin reuptake inhibitors, and influence the activity of serotonin in nerve endings. SSRIs are sometimes combined with cognitive behavioral therapy (CBT) and this study may shed some light on why this combination works well for those who are depressed.
As Dr. Miyazaki notes in a release, “This could help explain why combined treatment of depression with SSRIs and Cognitive Behavior Therapy (CBT) is more effective than just SSRIs alone. The psychological boost of the therapy is enhanced by raised serotonin levels.”
The study is published in Nature Communications.