Culture, education and of other forms of acquired capacities act on individual differences in skill to shape how individuals perform cognitive tasks such as attentional and executive control. Of interest, the use of more than one language (bilingualism) also appears to be a factor that shapes individual performance on tests of cognitive functioning. Indeed, researchers have shown that a bilingual can have better attention and executive control capacities than monolingual speakers and this is argued to be due the ability to inhibit one language while using another. Beyond behavioral differences, bilingualism seems to affect brain structure as well. Recent evidence also shows bilinguals develop more gray matter in crucial brain areas responsible for executive control, hence, providing a neurological basis for why bilinguals outperform monolinguals on many attentional control tasks. It has been postulated that this cognitive advantage offers protection to bilinguals against cognitive decline in aging. Bilingualism affords a cognitive reserve in the form of a set of skills that allows some people to cope with cognitive decline such as mild cognitive decline or Alzheimer's disease better than others. The primary aim of the studies here performed was to investigate if and how the bilingual brain becomes more resistant to cognitive decline. Three combined comparative behavioral and structural neuroimaging studies were carried out in bilingual and monolingual seniors. The overall results show a rather interesting pattern of findings that may be summarized as follows: if well matched for demographic and behavioral variables such as age, socio-economic status, education, and global cognitive functioning, bilinguals have generally increased gray matter densities as compared to monolinguals in those brain areas that are known to be more affected by physiological aging such as the orbitofrontal cortex, the temporal poles and parietal lobules, and in areas involved in cognitive control such as the prefrontal cortex and the anterior cingulate cortex. Increased gray matter in these latter areas also correlates with the superior performance of bilinguals on executive control tasks. Interestingly, in order to keep such a neural benefit (i.e. increased gray matter density) the degree of proficiency of the second language has to be relatively high and bilinguals have to be constantly exposed to their second language. Finally, specifically for the aging population, age of second language acquisition has no major role in determining putative neural differences. Any putative neural differences between bilingual speakers are determined by factors such as the degree of proficiency and exposure to a second language. In conclusion, as thoroughly investigated here, bilingualism represents a neural reserve for healthy aging. However, the benefits are most prominent when second language proficiency and exposure are kept high. / published_or_final_version / Education / Doctoral / Doctor of Philosophy

The group of people aged 85 years and older is the fastest growing chronological population on the United States (Neal et al., 1993), and while a considerable amount of research has focused on the language of the elderly (those over 65 years), relatively little study has focused specifically on those aged 85 and older. This study is valuable in that it includes a large sample of optimally healthy people aged 85 and older. This sample of the optimally-healthy oldest-old will help define what changes, if any, are a function of age alone and what changes are clinical (associated with some disease, neurologic complication, or psychological impairment). The purpose of this study was to compare two groups of elderly people's use of cohesion during an expository discourse task. This study also sought to answer the following question: If no health problems exist, does age alone affect the cohesion in the expository discourse of the elderly? To effect this comparison, a comparison of cohesive use in a group of 12 people between the ages of 65 and 75 years (the young-old) was contrasted with cohesion used by a group of 27 people aged 85 years and older (the oldest-old). The subjects were gathered as part of the Oregon Brain Aging Study under the direction of doctors Diane Howieson and Jeffrey Kaye of the Portland VA Medical Center. The subjects had to meet strict inclusion and exclusion criteria. As part of the evaluations for the Oregon Brain Aging Study, each subject was audiotaped while describing the fishing picture from the Neurobehavioral Cognitive Inventory (Kiernan et al., 1987). Each sample was then transcribed, divided into T-Units, and analyzed according to the cohesive analysis designed by Liles (1985) and Liles et al. (1989). Group comparisons for each aspect of cohesion (frequency, style, and adequacy) was completed using a 1- test. No significant differences at the .05 level were found on any of the measures.