This article from the New York Times, is about a discovered process of synaptic pruning which is normal and necessary in the developing brain, but if it continues out of control in adolescence it can lead to to schizophrenia.  The pathological process may be linked to an autoimmune disorder where the glial cells of the brain are inappropriately flagged for destruction and the synaptic connections of the brain’s neurons are diminished, leading to a less dense pre-frontal cortex.