Various techniques have been developed to image human brain function in the past decade. X-ray computerized tomography and magnetic resonance imaging (MR) are used to evaluate brain structure. Recently, positron emission tomography (PET) and MR are often utilized to perform human brain mapping such as attention, cognition, language comprehension, and so on. PET also makes it possible to evaluate the states of various types of neurotransmission. These techniques cannot only be used to map 'brain neurochemistry' in normal human brains, but they will also increase our knowledge by demonstrating neurochemical abnormalities in a wide range of neurological and psychiatric disorders or those that occur during normal aging. The PET techniques are applicable to the development of new drugs in the pharmaceutical industry. Using PET techniques of imaging neurotransmission, it is feasible to measure the release of neurotransmitter after activation of the CNS by various methods (ligand activation study). We have developed the methodology of using 11C-labeled antagonists for mapping functional histamine H1-receptors in human brain directly and noninvasively by PET. The present review article provides an outline of the conceptual and methodological progress over the past several years that has made it possible to visualize neurotransmission in human brains by PET.
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