on the relative severity of different types of symptoms, and an ongoing debate concerns how best to account for the imperfect correspondence between the clinical diagnostic entity and the underlying neurobiology (Hyman, 2007). An additional complication arises when considering the stage of the disorder. Results from several longitudinal studies have indicated that decreases in gray matter volume become more pronounced over the course of the disorder. It is not known to what extent the progressive gray matter loss is a fundamental aspect of the disease process, is due to treatment with antipsychotic medications, or occurs as a response to the stress and potential environmental hardships associated with having a chronic severe psychiatric illness. A notable finding has been that individuals who develop schizophrenia during childhood appear to have a much more rapid and severe loss of cortical gray matter than those with the more typical onset in early adulthood, raising the additional question of how disease-related factors interact with normal brain developmental processes (Thompson, Vidal, et al., 2001).
