Schizophrenia

Schizophrenia is a disorder whose symptoms fall into three groups. Here, positive does not mean good. Positive symptoms are experiences that appear, such as hallucinations, which are perceptions of something that isn't there, and delusions, which are firm beliefs that don't match reality. Negative symptoms are things that decrease, such as motivation and expressiveness. The third group is cognitive impairments, such as those affecting memory, executive function, which is the ability to organize and plan, and the speed at which the mind processes information.

What happens inside? This is where dopamine comes in, a chemical messenger that neurons use to communicate and that travels along different pathways in the brain. Picture a house with a speaker in every room. In one pathway, the mesolimbic pathway, there is thought to be excess dopamine activity, like a speaker playing too loud, and this is thought to contribute to positive symptoms. In another, the mesocortical pathway, dopamine levels may be low, like a speaker turned almost all the way down, and that may underlie the negative and cognitive symptoms.

The case is not closed. Schizophrenia arises from complex interactions between genetic and environmental risk factors, and no current model can explain all the changes that have been observed.