Sampriti Roy, University of Calcutta
Serotonin is one of the most famous neuromodulators of behaviour. It helps regulate mood, is required for motor skills and cognitive functioning and is significant in maintaining overall health. However another important trait which serotonin is responsible for has been found out by a study conducted by the Neural Computation Unit at the Okinawa Institute of Science and Technology Graduate University (OIST). With Dr. Katsuhiko Miyazaki and Dr. Kayoko Miyazaki as authors, the research shows that release of serotonin plays a crucial role in promoting patience.
The study draws heavily on prior research, where a powerful technique called optogenetics — using light to stimulate specific neurons in the brain — was used by the Neural Computation Unit to establish a causal link between patience and serotonin. Genetically engineered mice bred by the scientists had serotonin-releasing neurons that expressed a light-sensitive protein. This meant that the researchers could stimulate these neurons to release serotonin at precise times by shining light, using an optical fiber implanted in the brain. It was found that stimulating these serotonin-releasing neurons while the mice were waiting for food increased their patience, with the maximum effect seen when the likelihood of receiving a reward was high but the timing of the reward was uncertain.
The previous study on this topic focused on the mice brain showed that serotonin-releasing neurons from the part called dorsal raphe nucleus (DRN) breach many other areas of the fore-brain. In the recent study, the scientists explored specifically which of the brain areas contributed to regulating patience. Three areas that were shown to increase impulsive behaviors when they were damaged, including the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), and orbitofrontal cortex (OFC), we’re focused on by the team.
It was observed that serotonin stimulation in the orbitofrontal cortex (OFC) is nearly as effective as that in the dorsal raphe nucleus (DRN) for promoting waiting, while in the nucleus accumbens (NAc), it does not promote waiting. By varying the times when the mice would be rewarded with food, the researchers found that serotonin stimulation in the medial prefrontal cortex (mPFC) promotes patience only when the timing of future rewards is not fixed.
The study presently in the discussion is a step towards gaining further understanding of the action of serotonin on different areas of the brain, which could have significant implications. The study presents a scope of being useful in therapy, future development of drugs such as SSRIs (selective serotonin reuptake inhibitors) used to treat depression and potentially, saving human lives.
Also read: Differential gene expression regulation suggesting brain evolution
Source: https://advances.sciencemag.org/content/6/48/eabc7246.full
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