The adaptive brain: aging and neurocognitive scaffolding

Abstract

There are declines with age in speed of processing, working memory, inhibitory function, and long-term memory, as well as decreases in brain structure size and white matter integrity. In the face of these decreases, functional imaging studies have demonstrated, somewhat surprisingly, reliable increases in prefrontal activation. To account for these joint phenomena, we propose the scaffolding theory of aging and cognition (STAC). STAC provides an integrative view of the aging mind, suggesting that pervasive increased frontal activation with age is a marker of an adaptive brain that engages in compensatory scaffolding in response to the challenges posed by declining neural structures and function. Scaffolding is a normal process present across the lifespan that involves use and development of complementary, alternative neural circuits to achieve a particular cognitive goal. Scaffolding is protective of cognitive function in the aging brain, and available evidence suggests that the ability to use this mechanism is strengthened by cognitive engagement, exercise, and low levels of default network engagement.

Figure 1

Cross-sectional aging data adapted from Park et al. (2002) showing behavioral performance on measures of speed of processing, working memory, long-term memory, and world knowledge. Almost all measures of cognitive function show decline with age, except world knowledge, which may even show some improvement.

Figure 2

Cross-sectional and longitudinal aging brain volumes across various brain regions (adapted from Raz et al. 2005). Each pair of line-connected dots represents an individual subject’s first and second measurement. The caudate, hippocampal, cerebellar, and frontal regions all show both cross-sectional and longitudinal reduction in volume with age. The entorhinal, parietal, temporal, and occipital regions are relatively preserved with age.

Figure 3

Frontal bilaterality is increased with age. (Left side) Left lateralized frontal engagement in young adults during a verbal working memory task; in older adults, an additional right frontal engagement is observed (adapted from Reuter-Lorenz et al. 2000). (Right side) Right lateralized engagement in young adults and low-performing older adults during a long-term memory task, and bilateral frontal engagement in high-performing older adults (adapted from Cabeza et al. 2002).

Figure 4

A conceptual model of the scaffolding theory of aging and cognition (STAC).