" In the 1960s, depression was thought to be a matter of having too little of the neurotransmitter norepinephrine. Then, a few years later, the theory changed to a deficiency of serotonin. We now know it’s much more complicated. Sure serotonin and norepinephrine are involved, but so are dopamine and numerous other neurochemicals. "

― Alex Korb , The Upward Spiral: Using Neuroscience to Reverse the Course of Depression, One Small Change at a Time