Brain chemical makes humans more patient

The brain chemical serotonin that is widely targeted to treat depression also helps humans have patience in life, researchers report.

To investigate the role of serotonin in patience, the researchers used a task in which mice have to wait for a reward that arrives at random times.

During some of the trials, they stimulated serotonin neurons using a technique called optogenetics.

"We made serotonin neurons sensitive to light so when we illuminated them, they were activated and released serotonin in the brain," said Madalena Fonseca, member from the team of lead researcher Zachary Mainen at the Champalimaud Centre for the Unknown (CCU) in Lisbon, Portugal.

The scientists observed that when they activated serotonin neurons, mice became more patient.

"The more serotonin neurons were activated, the longer the mice would wait," added Masayoshi Murakami, another member of the CCU team.

Scientists also performed experiments to test if stimulation of serotonin neurons could act as a reward.

"If the sensation of serotonin was pleasant or rewarding for the mice, this could have explained why they waited longer", Fonseca noted.

To do this, they tested whether mice preferred to perform actions associated with serotonin stimulation.

The results of these experiments were negative, ruling out that increased patience was a consequence of reward.

This study has implications for understanding the involvement of serotonin in depression and other diseases.

Because antidepressants are thought to increase serotonin, people assume that more serotonin neuron firing would feel good.

"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," Mainen concluded in a paper appeared in the journal Current Biology.