Life-Span Development

Most developmental research describes what is normal, not what is possible. Referring to Table 1, another main theme in life-span developmental theory is associated with plasticity, reserve capacity, and resiliency. Plasticity refers to the potential for intra-individual change. Intra-individual plasticity is evident when there is variability in levels of performance across different kinds of tasks or when there is variability in performing the same task measured at different times or under different conditions. Even the mature adult brain retains considerable functional plasticity, and there is continued cortical reorganization based on adult experience (e.g., Greenough and Black; Ramachandran). Life-span researchers are interested in understanding developmental differences in the gap between observable behavior and actual or potential competence. The potential for optimization is present throughout the life course, although it is likely that it becomes increasingly constrained near the end of the life span. In other words, there appears to be diminished reserve capacity near the end of the life span, such that the individual is vulnerable to a variety of circumstances associated with mortality.

Individuals also exhibit varying capacities to protect themselves from impairment and insult associated with aging and disease, and to adapt effectively to the demands of stressful situations. The term reserve capacity refers to the individual's resources for responding effectively to challenging conditions. The term resiliency is similar in its meaning, and refers to a capacity for successful adaptation and recovery in response to stressful life events. Although the concept of resilience has been used mainly in reference to protective resources in children, recently some life-span researchers have argued that resilience is a useful concept for describing individual adaptation throughout the life span.

The concepts of plasticity and reserve hold promise for providing a full understanding of the relationship between aging and behavior. Analogous to cardiovascular function, or muscular efficiency, healthy older adults usually function quite effectively in everyday nonstressful conditions, but their functioning is likely to be impaired under stressful conditions. That is, age-related deficits in behavioral function are most apparent when systems that are critical to maintaining performance are challenged or stressed. The study of reserve capacity is useful for describing the effects of aging on a wide range of functions under challenged conditions. Along these lines, work by Baltes and colleagues has addressed how selected aspects of development can be enhanced or compensated for in situations or domains where there is optimal support.