What does this tell us about the possible causes of the negative symptoms of schizophrenia?

Schizophrenia Symptoms Schizophrenia presents with both positive symptoms, which are behaviors more pronounced than in non-schizophrenic individuals, and negative symptoms, which are behaviors that are less pronounced than in non-schizophrenic individuals. While the positive symptoms are reasonably well treated by current pharmaceuticals, the negative symptoms are not. What does this tell us about the possible causes of the negative symptoms of schizophrenia?