Glycogen phosphorylase a (GPa) is correlated with metabolic activation, suggesting its potential use as a marker for neuronal activity. In dentate gyrus, GPa patches are induced by glutamate infusion. Hippocampal electroencephalogram (EEG) and neuronal firing rates are modulated by behavioral state, and cell discharge is suppressed by restraint. In rats, under conditions of free exploration, passive movement under loose or secure restraint, quiet wakefulness, and anesthesia, GPa activity and 6-10-Hz theta power were inversely related: The more active the animal, the stronger the theta rhythm and the lower the GPa activity. Thus, GPa was least under conditions in which the hippocampus processes external information, and at intermediate levels during restraint, when neuronal firing is lowest. This dissociation raises doubts about the use of metabolic activity as an indicator of changes in neuronal activity or of information processing per se.