1987 Scandinavian researchers perform an experiment to measure serotonin levels in the brains of patients. They find higher levels in depressed patients which contradicts the suggestive findings of a prior study done ten years earlier which "suggested" that depressed patients typically have lower levels in the brain compared with the controls of that experiment.
1994 In a study done at McGill University in Montreal, male subjects were given a chemical mixture concocted to lower serotonin levels in their brains. Even though their serotonin levels were extremely decreased, the subjects showed no significant changes in their mood.
2011 The New Neuron TheoryIn the late 1980s a neuroscientist named Fred Gage and his collaborators began studying the hippocampus, the part of the brain that deals with emotion. The idea that adult humans did not produce new neurons was fairly accepted but in initial tests on mice Gage found new evidence to the contrary. After applying external environmental stressors on mice, effectively "stressing them out", he found a low level of neuron production in their brains. Conversely, mice that were less exposed to stress that remained physically active in an enriched environment were found to have more neurons being produced. In 2011, working from these studies, Rene Hen, a neuroscience at Columbia University began testing antidepressants on depressed monkeys. He found that the drugs only worked when new nerve cells were able to grow and new neurons could be produced. The drugs were ineffective when neuron production was blocked.