The main goal of the proposed research is to use functional magnetic resonance imaging (fMRI) to elucidate the effects of aging on the neural correlates of cognition. In particular, we will investigate the generalizability and functional significance of the finding that brain activity during cognitive performance tends to be less lateralized between the left and right hemispheres in old adults than in young adults. To investigate the generalizability of age-related asymmetry reductions across cognitive tasks, we will compare the effects of aging on brain activity during episodic memory encoding, episodic memory retrieval, semantic memory retrieval, and working memory. To investigate the generalizability of age-related asymmetry reductions across the adult population, we will investigate individual differences in cognitive performance, education, and frontal-lobe function, and will examine a large group of subjects evenly distributed from young to old age. To investigate the generalizability of age-related asymmetry reductions across the brain, we will analyze brain activity data using a regions-of-interest (ROIs) approach, and will calculate a lateralization index for each ROI. ROI analyses will be complemented with voxel-wise analyses. Finally, to investigate the functional significance of age-related asymmetry reductions, we will test compensation and dedifferentiation hypotheses by correlating brain activity with cognitive performance and by using event-related fMRI analyses. According to the compensation hypothesis, age-related asymmetry reductions reflect an age-related reorganization of brain functions that is beneficial for cognitive performance. According to the dedifferentiation hypothesis, it reflects an age-related difficulty in engaging specialized neural mechanisms. Deciding between these hypotheses has important practical implications. For example, if age-related asymmetry reductions reflect a compensatory mechanism, bihemispheric involvement could be targeted as a goal of cognitive rehabilitation programs. The proposed research program has direct implications for the promotion of health. Understanding the neural basis of cognitive functions in the normal brain is a precondition for any rational attempt to cure or rehabilitate cognitive deficits due to brain dysfunction, Moreover, understanding the neural basis of age-related cognitive deficits will eventually allow the development of drugs and rehabilitation methods to ameliorate these deficits.