Researchers take three general methodological perspectives in tackling the neuroscience of aging: the neuropsychological, the correlational, and the activation imaging approach (see Cabeza, 2004). The neuropsychological approach compares brain functioning of healthy older adults with adults displaying various pathological disorders in the brain. In this approach researchers are interested in whether patients of any age with
42 CHAPTER 2 damage in specific regions of the brain show similar cognitive deficits to those shown by healthy older adults. If this is the case, then researchers can conclude that decline in cognitive functioning as we grow older may be related to unfavorable changes in the same specific regions of the brain observed in the brain-damaged patients. This type of comparison is typically made between healthy older adults and patients showing frontal lobe damage. For example, patients with brain damage in the frontal lobe display lower levels of dopamine (an important brain transmitter substance), which results in a decrease in speed of processing (resembling what is observed in healthy older adults). Another important objective of research using this approach is to isolate the neural or brain mechanisms that are associated with both normal and pathological decline in cognitive functions. These findings stimulate theoretical development by identifying influential factors that warrant theoretical explanation as to how and why these factors may cause cognitive decline as we age.
The correlational approach attempts to link measures of cognitive performance to measures of brain structure or functioning. For example, a researcher may be interested in the correlation between cognitive behavior, such as the ability to control the contents of the conscious mind using working memory, and neural structural measures, such as the volume of the brain (Raz, 2000). This example focuses on the role of brain structure in explaining cognitive decline (see Raz, 2000). Instead of direct measures of brain structure or functioning, some researchers investigate the correlation between behavioral tests that are associated with the function of specific brain regions (e. g., frontal lobe tests). However, this latter approach is more speculative in that there can be much uncertainty as to whether the tests accurately reflect anatomical and functional authenticity of the specific brain region under investigation.
Finally, the activation imaging approach attempts to directly link functional brain activity with cognitive behavioral data. This approach allows the in vivo investigation of changes in brain