Cerebral blood flow activation and functional lesions in schizophrenia

This article reviews functional neuroimaging studies which measure task-specific changes in neuronal activity in schizophrenia, usually indexed by cerebral blood flow. Twenty-four published reports employing an activation strategy to study schizophrenia are reviewed. Eleven of these studies examined prefrontal function in schizophrenia, mostly with the Wisconsin Card Sort, and almost all have found some failure of the patients to demonstrate task-related increases in prefrontal blood flow. However, activation studies using simple sensory and motor tasks have also demonstrated abnormal activation, both as excessive and as deficient neuronal responses. A picture of a generally poor ability to organize brain activity emerges in schizophrenia. Dysfunction in a specific region, such as the prefrontal cortex, may indicate a primary functional lesion of the illness, or a salient feature of more widespread dysfunction of distributed and interactive brain networks. Progress in understanding will depend upon better knowledge of the functional neuroanatomy of the brain and the employment of neurobehavioral probes which can reliably assess a spectrum of brain networks which produce simple as well as complex function.