Dr. Weinberger stated that substantial evidence indicates that biological risk for schizophrenia appears early in life, long before onset of clinical symptoms. Consistently, obstetric complications have been reported to correlate with abnormal neuro-imaging findings in adulthood, and large, population-based epidemiologic studies have reported abnormalities in motor, cognitive and social development as early as the first year of life.

Although researchers have described subtle neuro-cellular pathology in brains of schizophrenic patients, that pathology has not been associated with neuronal degeneration, which must exist, according to Dr. Weinberger, to corroborate the neurodegenerative hypothesis.

Some researchers have inferred that neurodegeneration occurs in schizophrenia based on observations that some patients show worsening symptoms and increasingly poor response to anti-psychotic medication over time. According to Dr. Weinberger, those observations may reflect factors other than neurodegeneration, such as cumulative effects of disability and its psychosocial consequences.

Other evidence cited in support of neurodegeneration derives from longitudinal assessment of schizophrenic patients with magnetic resonance imaging scans. Yet, those findings have been inconsistent, with some studies reporting left hemispheric abnormalities and others abnormalities of the right hemisphere or frontal lobe. Although most studies have reported reduced hippocampal volume, one study reported the opposite. Of those reporting reduction of hippocampal volume, the degree of reduction conflicts with that observed in post-mortem observations.

Dr. Weinberger does not believe that abnormalities observed during longitudinal MRI monitoring represent neurodegeneration.