Brain Energetics and Neuronal Activity: Applications to fMRI and MedicineUpplaga 1

Recent in vivo NMR studies of the brain have identified important metabolites and have measured their flows in animals and humans. 13C labeled molecules have been particularly important for these studies because the low 13C natural abundance allows labeled metabolites to stand out in NMR spectra. Flows of labeled glucose into the glutamate, glutamine and GABA cerebral pools, measured by 13C NMR, establish the rate of glucose oxidation. In the same experiment, the rates of glutamate and GABA neurotransmitter release and recycling can be measured. Methods for performing these experiments and for interpreting the signals are described in this book, which provides the first integrated account of this rapidly growing field of functional, cerebral metabolism. The thermodynamic relations between energy and work show that the brain efficiently uses its energy to support a high baseline level of neuronal activity in the absence of stimulation. These results lead to a proposed reformulation of fMRI experiments which have traditionally discarded the high baseline activity. States of mind particularly, as they bear upon mental illness, have been correlated with in vivo concentrations of GABA, while the energy/neuronal firing results in epileptic patients have opened the energetic basis of this disease to study and understanding. The quantitative, coherent picture emerging from these experiments solidifies our understanding of brain function and offers definite, novel insights into the processes of mental disorders.