Decoupling of structural and functional brain connectivity in older adults with white matter hyperintensities.

Age-related impairments in the default network (DN) have been related to disruptions in connecting white matter tracts. We hypothesized that the local correlation between DN structural and functional connectivity is negatively affected in the presence of global white matter injury. In 125 clinically normal older adults, we tested whether the relationship between structural connectivity (via diffusion imaging tractography) and functional connectivity (via resting-state functional MRI) of the posterior cingulate cortex (PCC) and medial prefrontal frontal cortex (MPFC) of the DN was altered in the presence of white matter hyperintensities (WMH). A significant correlation was observed between microstructural properties of the cingulum bundle and MPFC-PCC functional connectivity in individuals with low WMH load, but not with high WMH load. No correlation was observed between PCC-MPFC functional connectivity and microstructure of the inferior longitudinal fasciculus, a tract not passing through the PCC or MPFC. Decoupling of connectivity, measured as the absolute difference between structural and functional connectivity, in the high WMH group was related to poorer executive functioning and memory performance. These results suggest that such decoupling may reflect reorganization of functional networks in response to global white matter pathology and may provide an early marker of clinically relevant network alterations.

Aging and interference in verbal working memory.

According to inhibitory views of working memory, old adults should have particular problems deleting irrelevant information from working memory, leading to greater interference effects compared with young adults. The authors investigated this hypothesis by using variations of an A-B, C-D retroactive interference paradigm in working memory with young and old adults. They used a recognition measure of memory, assessing both accuracy and reaction time. The primary finding was that senior adults consistently exhibited proportionally greater retroactive interference effects compared with young adults when interfering word pairs that had been read aloud had to be rejected. Patterns of recognition and reaction time data suggested that old adults' activation of target material is similar to young adults, but they experience sustained activation of irrelevant material that has entered working memory. Theoretical implications of these findings for inhibitory deficit (R. T. Zacks & L. Hasher, 1998) and source memory deficit accounts of cognitive aging are discussed.

Aging, culture, and cognition.

There is evidence that East Asians are biased to process information in a holistic, contextual fashion, whereas Western Europeans process information in an analytic, feature-based style. We argue that these cultural differences in information-processing styles are so pervasive that they affect cognitive function at the most basic levels, including the mechanics of cognition. However, as individual age, it is not always the case that culture effects on cognitive processes magnify, despite many additional years of exposure to the culture. Neurobiological decline in cognitive function that occurs with age is a cognitive universal and can limit the strategies used in late adulthood, resulting in more similarity in cognitive function in late adulthood across cultures than is observed in young adulthood. We present a theoretical framework for understanding the impact of aging on cognitive function cross-culturally. The importance of developing culture-invariant measures of processing resources is emphasized and methodological issues associated with the cross-cultural study of aging are addressed.