Quantitative imaging of neuroreceptors in the living human brain

Positron emission tomography (PET) makes it possible for the first time to examine in living humans the chemistry of the brain, which relates the structures of the brain to the functions of the mind. PET scans make it possible to assess the state of neurotransmitter receptors, such as the dopamine, serotonin, muscarinic cholinergic, opiate, and benzodiazepine receptors, in different regions in normal persons and patients with neuropsychiatric diseases. One of the most striking findings to date is that dopamine receptors fall significantly between the ages of 19 and 73 years, to a greater degree in men than in women. The effects of neurotropic drugs, such as haloperidol and methadone, can be assessed in an individual patient, providing for the first time an objective indicator of the specific desired effects of such drugs in the treatment of nervous or mental disease. Studies of patients with diseases such as Parkinson's disease, Huntington's disease, Alzheimer's disease, bipolar disease, and schizophrenia are in progress. At present, the patients are being examined as part of research protocols, but it is likely that clinical trials will not be far off.