For many years, dopamine has been the neurotransmitter that researchers have focused on to explain schizophrenia. In what way has our understanding changed in recent years with regard to the dopamine hypothesis?

a) The focus on dopamine was a false lead based on research that was not replicated.
b) Although dopamine is a key neurotransmitter, its effects are complex, with levels that are elevated in some brain areas and decreased elsewhere.
c) Dopamine seems to play a key role in the development of schizophrenia only in cases in which serotonin levels are simultaneously at low levels.
d) The dopamine hypothesis has proven to be an accurate explanation for only certain types of schizophrenia, especially the more severe forms of the disease.

B