New Computational Model Analysis Reveals Serotonin Speeds Learning Process

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Researchers from Sainsbury Wellcome Centre revealed that serotonin plays vital role in speeding up learning.

The primary function of Serotonin is to communicate between neural cells and play an essential role in functional, and dysfunctional cognition. Many antidepressant drugs are made with capability to target Serotonin against depression, obsessive-compulsive-disorder and forms of anxiety. However, serotonin also contributes in cognition and decision-making, including punishment, reward and patience.

In a research led by neuroscientists Kiyohito Iigaya and Peter Dayan, the team carried out experiments on mice. The mice were trained to choose between two targets in return of a water reward. The mice had to continuously understand which of the two targets were more rewarding as the researchers kept changing the reward rates without warning. The team triggered serotonin release in the brain with genetically modified serotonin neurons to access the effects of serotonin on the learning process. This process called optogenetics was coupled with a computational model based on reinforcement learning principles. The team recorded the learning rate of mice with and without serotonin stimulation. The results showed that the learning rate in mice was higher when serotonin was induced. The results were published in the journal Nature Communications on June 26, 2018.

The researchers also noticed that the mice applied the ‘win-stay lose-switch’ strategy during the experiments. The mice repeated a choice that previously rewarded and switched to other choice if it did not reward. This behavior depicted that the mice made quick decisions. The serotonin stimulation did not affect these quick decisions. However, when the mice were slow in making decisions after repeated trials, they did not follow the win-stay lose-switch strategy. The animals choose to decide on the basis of longer history of rewards, which is a clear effect of reinforcement learning principle. This slow learning process was evident even when the mice made fast decisions with the win-stay lose-switch system. It proves that serotonin stimulation only boosted occasionally when the animals took more time to make decisions.

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