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.