I’m sure this research has more implications than currently realized.
Serotonin is thought to mediate communications between neural cells and play an essential role in functional, and dysfunctional, cognition. For a long time, serotonin has been recognized as a major target of antidepressants (selective-serotonin-reuptake-inhibitor (SSRIs) that are used to treat various psychiatric conditions, such as depression, obsessive-compulsive-disorder and forms of anxiety. However, serotonin in humans, and other animals, is associated with a bewildering variety of aspects of cognition and decision-making, including punishment, reward and patience.
In the experiments, mice were trained to choose one of the two targets to receive water rewards. Mice continually had to learn which of the targets was more rewarding, as the reward rates changed without warning. Crucially, sometimes serotonin release in the brain was temporarily boosted in mice with genetically modified serotonin neurons by a technique called optogenetics, allowing the effects of serotonin on learning to be assessed.
Iigaya built a computational account of mice behaviour based on reinforcement learning principles, which are widely used in machine-learning and AI. Iigaya found that the learning rate, i.e. how fast the modelled mice learn, was modulated by serotonin stimulation. He compared trials with and without stimulation of serotonin neurons, and observed that the learning rate was significantly faster when stimulation was delivered, meaning that boosting serotonin sped up learning in mice.
The authors conclude: “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.”
Substantial clinical research shows that SSRI treatment is often most effective if combined with cognitive-behavioural-therapy (CBT). The goal of CBT is to change maladaptive thinking and behaviour actively, through sessions that are designed for patients to (re)learn their way to think and behave. However, scientists have had limited understanding of how and why SSRI and CBT work together for treatments. The new findings point to a possible functional link between the two, with serotonin boosting the learning inherent to CBT, providing clues as to one of the roles that this neuromodulator plays in the treatment of psychiatric disorders.