Neuropharmacological intervention with monoaminergic drugs in healthy subjects can either augment, have no effect, or hamper brain function. We hypothesize that these population differences might be related to differences (high vs. low) in monoaminergic synaptic function which may be due to specific allelic variations in monoamine system genes (e.g., various synaptic proteins, synthetic enzymes, etc.). We wish to examine the effect of dextroamphetamine, a non-specific monoaminergic drug, on cognitive efficiency while subjects perform a variety of tasks including memory challenges with increasing cognitive load and varying rewards, selective attention and emotional processing. Further, in collaboration with other NIMH neuroimaging protocols, we wish to examine the neurophysiological correlates of these effects. We believe this protocol will provide a matrix for many investigations to elucidate important neurophysiological mechanisms that underlie normal cognition and cognitive efficiency. It is anticipated that these studies would be of potential 'pharmacogenetic' importance with regard to individual differences in the metabolism of monoaminergic drugs in normal health, aging and in disease.