tion that needs to be answered in order to establish the relationships among cognition, culture, and social engagement in later life.

What types of stimulation alone, or in combination, are effective? Another important question concerns the interrelationship among different types of stimulation—intellectual, social, and physical. There is increasing evidence that physical exercise may improve cognitive function (Colcombe and Kramer, 2003), and it is possible that physical and intellectual stimulation interact with social engagement, conferring maximal neurocognitive protection. Alternatively, perhaps it is the quantity rather than the type of stimulation that makes the difference. This is an entirely unexplored question that is worthy of systematic evaluation.

The relationship between social engagement and cognitive health deserves serious research attention because of its potential implications for successful aging in America. There is a broad array of techniques for measuring the interactions between social engagement and cognitive health. Specifically, from the neuroimaging literature there is increasing evidence that older adults may use different neural routes to perform a cognitive task than young adults do (Cabeza, 2002; Park et al., 2001; Reuter-Lorenz, 2002) and that there is more plasticity in neural pathways than was previously understood. The use of neuroimaging tools to understand the effect of engagement manipulations on cognition is important and may reveal other effects as well. Research in both the social and the cognitive psychology of aging has provided rich theoretical models that can be extended to understand the role of social engagement in productive aging. Even more broadly, a full complement of sociological, behavioral, physiological, and neurobiological measures are available to measure both neural and behavioral outcomes of associations between social engagement and cognitive function. Furthermore, the outcome of research on motivation and behavior change and on socioemotional influences on decision making will directly affect the design of any interventions needed to increase social engagement.

Understanding the mechanisms underlying the causes and effects of social engagement, and discovering the types of activities that might maintain and even improve cognitive function is a major issue for public health policy and for the lives of the older population. Identifying culturally appropriate programmatic interventions that would make a contribution to delaying the onset of dementia would have major effects on the number of cases and on the demands on the health care system and on families.