response to serotonin as well as to the amount. The change in sensitivity
takes several weeks.
THE HIPPOCAMPUS NEUROGENESIS THEORY. Another theory has to
do with the manufacture of new cells in the hippocampus, which as you’ll
remember is the little seahorse in the brain that seems to be involved in
modulating many emotional processes. Based on the research of Selye and
others, we know that stress creates chemicals called glucocorticoidsthat kill
nerve cells in the hippocampus and elsewhere. A few studies have found
that the depressed have smaller hippocampi than other people. Normally,
the hippocampus grows its own new cells. But according to the theory,
neurogenesis is stopped or reversed by stress and started again by sero-
tonergics. The time lag is equal to the time it takes new cells to mature.
But intriguing as neurogenesis theory is, it’s mainly speculation based
on animal studies. Also, it requires an initial period of undefined “stress” to
explain why cells start dying in the first place, which brings everybody’s
favorite vague psychological concept into play in explaining the physiology
of depression. There’s also the question as to whether a medication that stim-
ulates the growth of new brain cells is a treatment or a form of disease.
Even more difficult to explain than the time lag from serotonin
increase to depression decrease is the fact that sometimes serotonergics
simply stop working. Medications that at one time controlled depression
quite well can cease doing so after about a year of treatment. Switching
to another, chemically similar drug can restart the antidepressant effect.
As you would imagine, there are theories to explain this phenomenon as
well, but at this point there is little research to back them up.
Though medications that increase the amount of available serotonin
and/or norepinephrine can do wonders for alleviating the symptoms of
depression, it seems that the disorder is something more complex than the
neurotransmitter deficiency you see advertised in magazines.
But What Is Depression?
To a clinician, depression consists of four related symptom complexes that
may have different neurophysiological correlates. Really, there isn’t much
of a dividing line between the complexes. One grades seamlessly into the
154 ❧Explosions into Sadness