Serotonin helps boost learning

Serotonin - one of the main chemicals that nerve cells use to communicate with each other - enhances the speed of learning, a study has found.

For a long time, neuroscientists have been set on constructing an integrated theory of what serotonin actually does in the normal brain.

Scientists from the Champalimaud Centre for the Unknown (CCU) in Portugal, and the University College London (UCL) in the UK created a mathematical model to pin down serotonin's function, especially for learning.

"The study found that serotonin enhances the speed of learning", said Zach Mainen, one of the study's leaders.

"When serotonin neurons were activated artificially, using light, it made mice quicker to adapt their behaviour in a situation that required such flexibility," Mainen said.

"That is, they gave more weight to new information and therefore changed their minds more rapidly when these neurons were active," he said.

Serotonin has previously been implicated in boosting brain plasticity, and this study adds weight to that idea, thus departing from the common conception of serotonin as a mood-enhancer.

The finding may help to better explain why selective serotonin reuptake inhibitors (SSRIs) - a class of antidepressants that are thought to act by increasing brain levels of circulating serotonin - are more effective in combination with behavioral therapies, based on the reinforced learning of behavioral strategies to stave off depressive symptoms.

In the experiments, mice had to perform a learning task in which the goal was to find water.

"Our results suggest that serotonin boosts [brain] plasticity by influencing the rate of learning. This resonates, for instance, with the fact that treatment with an SSRI can be more effective when combined with so-called cognitive behavioral therapy, which encourages the breaking of habits in patients," researchers said.