Aging, intelligence, and anatomical segregation in the frontal lobes

In this paper we propose a specific neuroanatomical theory of cognitive aging. We review evidence supporting the growing consensus that normal adult age changes reflect differential deterioration of the frontal lobes of the brain. Important differences in the pattern of spared and impaired abilities classically linked to aging or frontal lesions are highlighted. Capitalizing on neuropsychological and neuroimaging findings, the notion of functional and anatomical segregation within the frontal lobes is introduced, suggesting that the frontal cortex is not equipotential. In particular, the dorsolateral and orbitoventral prefrontal regions are called upon by distinct cognitive and behavioral functions. A detailed analysis of the literature suggests that only functions associated with dorsolateral regions are impaired with age, while orbitoventral functions are spared. The hypothesis is advanced that cognitive aging could be better interpreted in terms of changes in dorsolateral prefrontal cortex rather than an all-encompassing "frontal" deterioration. Finally, the role of modularity in cognitive aging and frontal lobe function is discussed.