In this project we intend to develop non-invasive methods to quantitively assess cerebral metabolism during functional activitation. The hypothesis of this project is that brain functional activation alters cerebral glutamate turnover. The basis for this assumption is that the measurement of glutamate turnover reflects the rate of the tricarboxylic acid (TCA) cycle and thus the cerebral metabolic rate of oxygen (CMRO2). Essential to ther performance of these studies will be experimental control and measurement of serum glucose, and insulin concentrations using the techniques employed for glucose clamps.