Does iq reduce with age

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The Impact of Aging on IQ: A Comprehensive Analysis

Decline in Cognitive Abilities with Age

Performance IQ vs. Verbal IQ

Research indicates that IQ generally declines with age, but the rate and onset of decline differ between performance IQ and verbal IQ. Performance IQ tends to decline earlier and more rapidly, while verbal IQ declines later and more slowly. This pattern is observed in the general population, suggesting that different cognitive abilities are affected by aging at different rates.

Influence of Physical Health

The decline in fluid intelligence, which involves the capacity to solve novel problems, is fully mediated by physical health. Diseases of the circulatory and nervous systems are significant mediators of this decline. In contrast, crystallized intelligence, which involves the use of knowledge and experience, is not mediated by physical health. This implies that maintaining good physical health can mitigate some of the cognitive declines associated with aging.

IQ and Cognitive Reserve

Cognitive Reserve Hypothesis

The cognitive reserve hypothesis suggests that individuals with higher IQs can better tolerate age-related brain pathologies. These individuals exhibit a later onset of terminal decline (TD) in cognitive abilities, although their rate of decline is steeper once it begins. Higher IQ is associated with a delay in the onset of TD by approximately 1.87 years for perceptual and motor speed and 1.96 years for verbal ability. This indicates that a higher IQ can act as a buffer against cognitive decline in old age.

Heritability of IQ

The heritability of IQ increases with age, reaching an asymptote at about 0.80 by the age of 18-20 and continuing at that level into adulthood. Shared environmental influences decrease across age, stabilizing at about 0.10 by adulthood. This suggests that genetic factors play a more significant role in IQ as individuals age, while environmental factors become less influential.

Age-Related Performance in Cognitive Tasks

Two-Choice Tasks and Memory

Studies examining the effects of aging and IQ on performance in two-choice tasks (e.g., numerosity discrimination, recognition memory, and lexical decision) show that declines in performance with age are not significantly different between low and high IQ subjects. However, IQ has a substantial impact on the quality of evidence obtained from stimuli or memory, affecting decision-making processes. Similarly, in memory tasks, IQ significantly influences performance, with higher IQ correlating with better accuracy and faster response times.

Timing Tasks

In timing tasks, increasing age and decreasing IQ are associated with greater variability in judgments of duration. However, older participants can still time events accurately on average, indicating that while precision may decline, the ability to perform the task remains intact.

Longitudinal Studies and Mortality

Premorbid IQ and Mortality

Longitudinal studies have found that higher IQ in early life is associated with lower mortality rates in middle to late adulthood. This relationship is not explained by reverse causality or selection bias, and adult socioeconomic position only partially mediates this association. This suggests that higher IQ may contribute to better health outcomes and longevity.

Conclusion

In summary, IQ does decline with age, but the extent and nature of this decline vary across different cognitive abilities. Performance IQ declines earlier and more rapidly than verbal IQ. Physical health plays a crucial role in mediating the decline in fluid intelligence, while crystallized intelligence remains relatively unaffected by health. Higher IQ provides a cognitive reserve that delays the onset of terminal decline, although the rate of decline is steeper once it begins. Genetic factors become more influential in determining IQ as individuals age, while environmental factors diminish in importance. Maintaining good physical health and leveraging cognitive reserve can help mitigate some of the adverse effects of aging on IQ.