Functional imaging studies: Linking mind and basic neuroscience

objective: The imaging of brain activity with positron emission tomography (PET) and functional magnetic resonance imaging has assumed a central posit ion in psychiatry. Functional imaging signals arise from changes in the neu rophysiological parameters of glucose and oxygen consumption mediated by bl ood flow. Method: Recent in vivo C-13 nuclear magnetic resonance (NMR) neurochemical studies have established a quantitative coupling between the rates of gluco se oxidation and glutamate neurotransmitter flux in rats and humans, thereb y linking measured neurophysiological parameters to brain function. Results: These results show that in the awake, resting, and unstimulated sl ates, 70%-80% of brain energy consumption is devoted to the same glutamate/ glutamine neurotransmitter signaling as are the small percentages stimulate d by tasks. Furthermore, in anesthetized animals, in which unstimulated act ivity is reduced, the total signal rather than a particular increment is re quired for a response. Conclusions: On this basis, the total signal, as well as the difference in the signal, measures cortical neurotransmitter flux. The total signal in a region therefore contains valuable information about required brain activit y Although signal change is often more easily measured, certain PET and C-1 3 NMR methods can quantify total regional signal activity and thereby provi de another measure of neurotransmitter activity.