up until i read this article, my understanding was that many, if not most, cases of depression were caused by low levels of the neurotransmitter serotonin. the research discussed in the article suggests that there are multiple types of serotonin receptors in the brain and that while some of them respond poorly to too little serotonin, others respond negatively to too much of it.
just further evidence that the brain is vastly complex, and for every discovery we make, there are thousands more to be understood. notice that the researchers and the journalist clearly state that the impact of serotonin is not yet understood.
is it any wonder that treatment is hard to get right?