Serotonin promotes perseverance, researchers find

March 9, 2018, Champalimaud Centre for the Unknown
Advanced techniques to directly control the activity of serotonin neurons in the brain are used to illuminate serotonin's biological functions. Credit: Champalimaud Centre for the Unknown/Sara Matias

How do increased serotonin levels affect behavior? This is a question that highly interests neuroscientists. Serotonin has multiple functions in the brain, and its effects are not completely understood. Serotonin is at the root of a whole class of antidepressant drugs, the most well-known of which is Prozac, that seem to work by increasing serotonin levels in the human brain.

Previous results have suggested that increased levels make animals (including people) more willing to wait for a reward—in other words, it was believed to increase patience. This was compatible with the idea that serotonin generally acts by inhibiting behavior, because in many cases, patience requires postponing an action.

But now, this idea has been challenged by an international team led by neuroscientists from the Champalimaud Centre for the Unknown (CCU), in Lisbon, Portugal. Their results have been published today in the journal Nature Communications.

The new study shows that serotonin promotes more than just passive waiting—it enhances active persistence in a task, even in the face of uncertain reward.

Persistence means actively following through on a task like completing homework, whereas many forms of patience require sitting tight and doing nothing. It so happens that the tasks used in the previous studies did not allow their authors to distinguish between patience and persistence. But in the new work, Eran Lottem, the first author of the paper, and his colleagues developed a task that is actually very similar to the natural situation animals face when foraging for food.

"We had some hints suggesting that the inhibitory effect of serotonin was not general. Some behaviors were unaffected by serotonin," says Lottem. "But we had never seen an active behavior promoted by serotonin. This is, to my knowledge, the first time such a behavior has been observed when serotonin-producing neurons are activated."

The mice were presented with the choice of two drinking sites placed at each end of a long rectangular box. At any given time, only one drinking site was ready to release water, so the mice had to roam back and forth between the two sides of the box to find the water, and to get it, they had to give a poke with their nose at the drinking site.

To mimic the unpredictability of real world situations, the experimenters arranged the experiment such that even an active drinking site did not always deliver water, so they would have to tolerate some unsuccessful pokes. This provided the scientists with a way to measure the persistence of the animals—they could count the number of pokes the mice were willing to give in order to try to get water at a "dry" site.

The scientists used a technology known as optogenetics to stimulate the serotonin-producing neurons using pulses of laser light delivered by an implanted optic fiber to the animals' brains. "What we saw was that when those neurons were stimulated, the animals were willing to poke longer even when they were not getting water, says Lottem. Therefore, serotonin was not inhibiting their behavior because, in that case, the mice would have given up sooner." In other words, he concludes, "the activation of promotes active persistence rather than mere patience."

Zachary Mainen, the lead author of this study, suggests that the results may lead to better treatments for depression, a disorder in which serotonin is implicated. "The difference between patience and persistence may sound subtle, but the implication is not: it could be the difference between quietly sitting in bed while the world goes by and jumping out of bed each day to greet it."

Explore further: Good things come to those who wait? More serotonin, more patience

More information: Eran Lottem et al, Activation of serotonin neurons promotes active persistence in a probabilistic foraging task, Nature Communications (2018). DOI: 10.1038/s41467-018-03438-y

Related Stories

Good things come to those who wait? More serotonin, more patience

January 15, 2015
In a study published today in the journal Current Biology, a team of scientists, led by Zachary Mainen at the Champalimaud Centre for the Unknown (CCU), found a causal link between the activation of serotonin neurons and ...

More serotonin, less motivation? It depends on the circumstances

February 14, 2017
A new study in mice shows that increasing serotonin, one of the major mediators of brain communication, affects motivation—but only in certain circumstances. Furthermore, the study revealed that the short and long term ...

Low risk of serotonin syndrome for triptans + SSRI/SNRI

February 27, 2018
(HealthDay)—A low risk of serotonin syndrome is seen in association with concomitant use of triptans and selective serotonin reuptake inhibitor (SSRI) or selective norepinephrine reuptake inhibitor (SNRI) antidepressants, ...

Study focuses on atomic structure of the serotonin transporter bound to SSRIs

January 29, 2018
New molecular research shows how chemically diverse drugs used to treat depression and anxiety disorders interact with the protein that transports serotonin in the brain. The discovery by researchers at the OHSU Vollum Institute ...

Researchers examine how opioids affect proteins in the brain other than opioid receptors

December 6, 2017
In a new study, researchers have characterized the effects of a series of opioids on proteins in the brain other than opioid receptors. In the British Journal of Pharmacology study, several synthetic opioids inhibited serotonin ...

When our world turns 'upside-down,' serotonin helps us deal with it

March 16, 2017
Serotonin, one of the major chemical messengers serving neuronal communication, is usually associated with the direct regulation of affective states and mood in general. But growing evidence suggests that one of the core ...

Recommended for you

When scientists push people to their tipping point

December 10, 2018
You probably overestimate just how far someone can push you before you reach your tipping point, new research suggests.

Internet therapy apps reduce depression symptoms, study finds

December 7, 2018
In a sweeping new study, Indiana University psychologists have found that a series of self-guided, internet-based therapy platforms effectively reduce depression.

Gender bias sways how we perceive competence in faces

December 7, 2018
Faces that are seen as competent are also perceived as more masculine, according to research published in Psychological Science, a journal of the Association for Psychological Science.

Targeted cognitive training benefits patients with severe schizophrenia

December 7, 2018
Schizophrenia is among the most difficult mental illnesses to treat, in part because it is characterized by a wide range of dysfunction, from hallucinations and mood disorders to cognitive impairment, especially verbal and ...

Pot withdrawal eased for dependent users

December 6, 2018
A new drug can help people diagnosed with cannabis use disorder reduce withdrawal symptoms and marijuana use, a new Yale-led study published Dec. 6 in the journal Lancet Psychiatry shows.

Link between neonatal vitamin D deficiency and schizophrenia confirmed

December 6, 2018
Newborns with vitamin D deficiency have an increased risk of schizophrenia later in life, a team of Australian and Danish researchers has reported.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.