Age-Related Changes in Neurochemical Properties
Advances have also been made in techniques measuring neurochemical changes in the aging brain, particularly in studies examining the role of brain dopamine (DA), a neurotransmitter substance that sends messages throughout the brain, in performance on various cognitive tasks (Backman, Nybert, Lindenberger, Li, & Farde, 2006). First, it is important to note that the dopaminergic system is associated with higher-level cognitive functioning like inhibiting thoughts, attention, and planning (Park & Reuter-Lorenz, 2008). In other words, high dopamine levels are linked to cognitive processing that is effortful and deliberate, but not to the processes that are more automatic and less effortful. To investigate dopamine, the majority of studies have used postmortem analyses, neuropsychological patient studies, and simulated modeling and the imaging of dopamine activity. Backman et al. (2006) have drawn several conclusions regarding this research. For example, there is increasingly clear evidence that effective functioning of the dopaminergic system declines in normal aging.
Researchers have found that declines in the dopaminergic system are related to declines in episodic memory and speed tasks (Backman, Ginovart, Dixon, Robins, Wahlin, Wahlin, Halldin, & Farde,
2000) , age-related deficits in working memory (Erixon-Linddroth, Farde, Robins, Wahlin, Sovago, Halldin, & Backman, 2005), as well as declines in memory (Yang, Chiu, Chen, Chen, Yeh, & Lee,
2003) . As we shall see in Chapter 6, these are cognitive tasks that are effortful and not automatic. Less age differences are observed in more automatic tasks like familiarity of information. Overall, the brief review of studies using molecular methods to examine dopamine changes with increasing age suggest that dopaminergic receptors play a role in cognitive aging. These studies expand our understanding of the neurochemical processes affected by increasing age that influence structural and cognitive changes.