A causal link between serotonin and the time mice were willing to wait was discovered by researchers from the Champalimaud Centre for the Unknown (CCU), according to Champalimaud Neuroscience Programme via PsyPost.
Serotonin is a neuromodulatory chemical used in the treatment of depression or chronic pain. A small group of cells in the brain, the raphe nuclei, are responsible for the release of serotonin, but according to CCU, what causes serotonin activity is still not fully understood.
By using a technique called optogenetics, scientists investigated how serotonin could affect the rats' patience when waiting for a reward. "We made serotonin neurons sensitive to light, so when we illuminated them, they were activated and released serotonin in the brain," said CCU team member Madalena Fonseca.
When serotonin neurons were activated, the mice were more patient, according to CCU. "We tested how different levels of activation influence waiting and saw that stronger activation resulted in longer waiting durations - the more serotonin neurons were activated, the longer the mice would wait," team member Masayoshi Murakami told CCU.
The scientists wondered if the serotonin was the reward that caused the mice to be more patient. "If the sensation of serotonin was pleasant or rewarding for the mice, this could have explained why they waited longer," said Fonseca.
The mice were tested to see if they preferred completing actions that would stimulate serotonin activation. The test results were negative, according to CCU. The researchers concluded that the willingness to wait was not due to reward.
"Because antidepressants are thought to increase serotonin, people assume that more serotonin neuron firing would feel good," study lead Zachary Mainen told CCU. "Our results show that the story is not so simple. That serotonin affects patience gives us an important clue that we hope will help us crack the serotonin mystery."
The team at Champalimaud will continue its research funded by the European Research Council. The results of this study were published in the Jan. 15 edition of the journal Current Biology.
