What purpose does it serve to the brain.
I have already googled,it waffled and never got to the point.
What affect has Serotonin on the brain.
It's a "neurotransmitter" ... helps brain communicate with itself.
Serotonin normal = brain transmitting signals frok one cell to another OK
Serotonin too low = depression (exact cause not determined)
Serotonin too high = serotonin poisoning http://en.wikipedia.org/wiki/Serotonin_syndrome
The honest answer is that besides being a neurotransmitter, we really don't know all its effects. It probably works in conjunction with other neurotransmitters and most likely isn't the only thing responsible for what we feel. Nobody really knows if low serotonin causes depression or if depression causes low serotonin. Lots of antidepressives raise serotonin in one way or another (SSRIs= serotonin selective re-uptake inhibitor) and it seems to help some people. Serotonin has effects on appetite, nausea, sexual behaviors, aggression, and fear too. There's a lot about the brain that we just haven't figured out yet and it's all probably more complex than what we think. There isn't a simple explanation...
Generally serotonin is a "feel good" "calming" hormone.