Age Differences in the Frontal Lateralization of Verbal and Spatial Working Memory Revealed by PET

TLDR

Age‑related decline in working memory is well documented, yet the neural basis of these changes remains largely unknown, with prior studies in younger adults showing lateralized verbal and spatial working memory organization. The study investigates whether bilateral activation in older adults reflects compensatory recruitment and other mechanisms underlying age differences in frontal lateralization of verbal and spatial working memory. PET was employed to examine 3‑second verbal and spatial short‑term storage in older and younger adults, using volume‑of‑interest analyses that compared activation in each hemisphere. Older adults displayed global anterior bilateral activation for both memory types, while younger adults showed left‑lateralized verbal and right‑lateralized spatial activation, and within frontal subregions older adults had bilateral rehearsal‑related activity and paradoxical dorsolateral prefrontal laterality.

Abstract

Age-related decline in working memory figures prominently in theories of cognitive aging. However, the effects of aging on the neural substrate of working memory are largely unknown. Positron emission tomography (PET) was used to investigate verbal and spatial short-term storage (3 sec) in older and younger adults. Previous investigations with younger subjects performing these same tasks have revealed asymmetries in the lateral organization of verbal and spatial working memory. Using volume of interest (VOI) analyses that specifically compared activation at sites identified with working memory to their homologous twin in the opposite hemisphere, we show pronounced age differences in this organization, particularly in the frontal lobes: In younger adults, activation is predominantly left lateralized for verbal working memory, and right lateralized for spatial working memory, whereas older adults show a global pattern of anterior bilateral activation for both types of memory. Analyses of frontal subregions indicate that several underlying patterns contribute to global bilaterality in older adults: most notably, bilateral activation in areas associated with rehearsal, and paradoxical laterality in dorsolateral prefrontal sites (DLPFC; greater left activation for spatial and greater right activation for verbal). We consider several mechanisms that could account for these age differences including the possibility that bilateral activation reflects recruitment to compensate for neural decline.