Hypofrontality in schizophrenia: influence of normalization methods

A systematic review and meta-analysis of the effects of antipsychotic medications on regional cerebral blood flow (rCBF) in schizophrenia: association with response to treatment

Evaluating the short- and long-term effects of antipsychotics on brain physiology is a key factor in advancing our understanding of neurophysiological changes in psychosis and improving prediction of treatment response. Understanding the nature of such changes is crucial to the interpretation of neuroimaging findings in patients with schizophrenia and psychoses in general. This review has systematically appraised existing evidence on resting cerebral blood flow (rCBF) in schizophrenia, before and after antipsychotic treatment, relating the findings to symptom severity. The review shows that antipsychotics exert regional effects on rCBF, particularly in frontal and basal ganglia regions, and that different antipsychotic generations have differential effects on rCBF. These findings are supported by an exploratory meta-analysis of a subset of studies. The review also highlights the relative lack of studies that use a priori definitions of treatment response, which is an important step in identifying testable hypotheses and ensuring clinical relevance of remission criteria. Finally, the review highlights important considerations for future psychopharmacological studies investigating the potential for rCBF to predict symptomatic improvement, which could inform the management of treatment in schizophrenia.

Hypofrontality in schizophrenia: a meta-analysis of functional imaging studies

OBJECTIVE

Hypofrontality is not a well-replicated finding in schizophrenia either at rest or under conditions of task activation.

METHOD

Studies comparing whole brain and frontal blood flow/metabolism in schizophrenic patients and normal controls were pooled. Voxel-based studies were also combined to examine the pattern of prefrontal activation in schizophrenia.

RESULTS

Whole brain flow/metabolism was reduced in schizophrenia to only a small extent. Resting and activation frontal flow/metabolism were both reduced with a medium effect size. Duration of illness significantly moderated resting hypofrontality, but the moderating effects of neuroleptic treatment were consistent with an influence on global flow/metabolism only. Pooling of voxel-based studies did not suggest an abnormal pattern of activation in schizophrenia.

CONCLUSION

Meta-analysis supports resting hypofrontality in schizophrenia. Task-activated hypofrontality is also supported, but there is little from voxel-based studies to suggest that this is associated with an altered pattern of regional functional architecture.

REGISTRATION AND NORMALIZATION TECHNIQUES FOR ASSESSING BRAIN FUNCTIONAL IMAGES

Tc-99m HMPAO is a typical tracer used in the analysis of cerebral blood flow. Single photon emission computed tomography (SPECT) brain imaging utilizing Tc-99m HMPAO is thus a popular method to assess brain function. In this paper, we present an image analysis system for SPECT images that performs a series of image processing procedures including 3D image registration, gray-level normalization, and brain extraction, which map all the 3D brain data to the same space for further analysis. Afterward, the aligned images undertake a standard statistical analysis, the paired t test, to detect the areas that have significant deviations between the two images. The statistical t map is then represented with a color plot for each brain slice to indicate the activation foci. The resulting maps are found very helpful to doctors for the lesion evaluation and localization in the clinical diagnosis of schizophrenic patients.

Chemical and physiologic brain imaging in schizophrenia

Technologic advances in functional brain imaging have provided exciting and informative insights into the functional neuroanatomy and neurochemistry of schizophrenia. Using MR spectroscopy, it has been possible to examine in vivo brain metabolism and to relate observed changes to physiological processes occurring at a cellular level. Positron emission tomography and single photon emission computed tomography have revealed disturbances of cerebral blood flow and glucose metabolism in patients with schizophrenia. More recently, these tools have also proved most useful in studying the relative receptor occupancy of typical and atypical antipsychotic medications.