1994 Muller and Knight 2006 Paulesu et al. This view was further supported by lesion studies showing that lesions in dorsolateral prefrontal regions are associated with poor performance on executive control tasks such as working memory, selective attention, and inhibitory control ( D’Esposito et al. Therefore, studies of aging typically viewed young adults in their twenties as being at their peak of neurocognitive functioning, followed by a steady linear decline. Frequently, gray matter (GM) in prefrontal regions (dorsolateral and orbitofrontal) was shown to decline linearly after adolescence or young adulthood ( Gogtay et al. Similarly, studies using anatomical neuroimaging techniques (e.g., CT and MRI) have reported structural changes and some have correlated these changes with neuropsychological test results ( Burgmans et al. ![]() 1983 Flood and Coleman 1988 Huttenlocher 1979 Terry et al. In support of this view, postmortem studies revealed microanatomical changes associated with aging such as changes in microscopic structure, and decreases in synaptic density, neuronal density and mean neuronal size (e.g., Anderson et al. 2002 Reuter-Lorenz and Lustig 2005 Tisserand and Jolles 2003). Traditional views of aging suggest that neurocognitive decline results from an inevitable loss of tissue and functional reserves ( Bellamy 1997 Cabeza et al. Therefore, we have added a middle-age group to our studies in order to better understand normal development across the lifespan as well as effects of pathology on cognitive functioning in the aging brain. This suggests that a young age group may not be the best control group for understanding aging effects on the brain since development is ongoing within this age range. In addition, recent results show that white matter tracts within the frontal and temporal lobes, regions critical for higher cognitive functions, continue to mature well into the 4th decade of life. ![]() The health of the elderly group has not been well-documented in most previous studies and elderly participants are rarely excluded, or placed into a separate group, due to health-related problems. Individuals with a history of hypertension, for example, are likely to have multiple white matter insults which compromise cognitive functioning, independent of aging processes. From our perspective, level of cognitive functioning achieved by a group of elderly is largely determined by the health of individuals within this group. Here we review a series of our own studies which lead us to an alternative interpretation, and highlights a couple of potential confounds in the aging literature that may act to increase the variability of results within age groups and across laboratories. Many neuroimaging studies of age-related memory decline interpret resultant differences in brain activation patterns in the elderly as reflecting a type of compensatory response or regression to a simpler state of brain organization.
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