Use-it-or-lose-it:investigating the cognitive reserve hypothesis and use-dependency theory

In popular psychology the use-it-or-lose-it theory has become accepted; that is, an increase in cognitive activity, particularly in later life, can reduce cognitive decline associated with both pathological and healthy aging. In the field of cognitive neuropsychology, the use-it-or-lose-it theory can represent either the cognitive reserve hypothesis or use-dependency theory. The cognitive reserve hypothesis states that an individual must be relatively cognitively active throughout life (particularly in early life) in order to build up a cognitive reserve to counter cognitive decline in old age. The use-dependency theory asserts that a high level of cognitive activity in later life is sufficient to attenuate or even reverse the cognitive aging process.

Questionnaire studies in this thesis have indicated that different cognitive activities have a greater effect on subjective measures of cognitive functioning. Specifically, the results showed that undertaking cryptic crosswords frequently appear to have a greater impact on cognitive awareness in older adults (compared to younger adults) than other cognitive activities. Furthermore, there was evidence that attempting cryptic crosswords encouraged older adults to form a realistic understanding of their current level of cognitive functioning, which suggested that such crosswords may be used as an intervention activity to promote cognitive functioning.

This was investigated by using a within-subjects intervention to examine the effect of regularly attempting cryptic crosswords on subjective and objective measures of cognitive functioning. The within-subjects approach eliminated potential mediating factors that may have influenced the impact of cognitive activity of cognitive interventions in previous studies (e.g. Jopp & Hertzog, 2007). The results confirmed that cryptic crossword participation enhanced cognitive awareness in older adults, particularly in those who could be regarded as being at-risk of sudden cognitive decline. However, there was no evidence that the intervention activity promoted objective measures of cognitive functions, which are known to decline with age (e.g. episodic memory, metacognition).

A within-subjects design was also used to manipulate stimulus characteristics to produce analogies of the cognitive reserve hypothesis and use-dependency theory. This technique bypassed the use of self-report measures of both cognitive activity and cognitive functioning, which may be intrinsically linked (e.g. Hertzog, 2009). These studies provided a modicum of support for the cognitive reserve hypothesis but no support for the use-dependency theory.

A novel model of the cognitive reserve hypothesis and use-dependency theory is presented which implicated the metacognition system as a key component that mediates the effect of cognitive activity on cognitive functioning in later life. The overarching findings suggest that an increase in cognitive activity in later life can enhance cognitive awareness but, due to an age-related deficit in the metacognitive pathway, older adults are unable to modify their behaviour to compensate for age-related cognitive decline in memory functioning. Thus, it can be concluded that cognitive activity in later life can produce changes in subjective but not objective measures of cognitive functioning. Future research needs to use similar within-subjects techniques to develop accessible cost-effective cognitive interventions, which specifically target the metacognition system.

Even though a copious amount of research has provided support for both theories, the link between cognitive activity and cognitive decline remains tenuous with no clear causal relationship (e.g. Salthouse, 2006). This thesis has taken in consideration whether the use of a between-subjects design, the measures of cognitive activity and the assessment of cognitive functioning used in previous research may have produced a disproportionate postulation of the effect that cognitive activity can have on cognitive functioning and decline in healthy adults.