Serotonin is a neurotransmitter associated with a number of cognitive disorders, namely depression, bipolar disorder and schizophrenia. Professor Trevor Robbins explains how the serotoninergic system works.

The serotonergic system is one of the oldest of the amine systems in the brain. It is also one of the most mysterious. It is very hard to say in a few words what the serotonergic system does. It originates in two midbrain areas called the dorsal raphe and the median raphe. They both innervate forebrain and midbrain structures in kind of complementary ways that are a bit complicated to go into. The serotonin system seems to be very much involved in inhibition. It opposes, in function, most of the other amine systems and it’s inhibitory both in terms of sensory input and in behavioral output. So, let me try and illustrate that - LSD is a drug which works via serotonin receptors in the brain and of course it produces amazing visual hallucinations by working with serotonin receptors and presumably, disinhibiting those neurons. On the output side, we know that serotonin is very much involved in impulsivity, that is to say, behavior occurring without foresight. We know in our own research with rats that if rats have low serotonin, they simply can’t restrain themselves from responding when they shouldn’t. So, this is a very intriguing function in terms of psychopathology. And in indeed in human terms, serotonin functions have also been linked to aggression, for example. So, low serotonin produces behavioral disinhibition leading to aggression.

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