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Peter Lichtenberg


The vascular depression theory suggests that cerebrovascular risk factors (CVRFs) are related to depressive symptoms. The activity limitation theory of depression suggests that relationships between medical burden and depression are due to limitations in activities. Past research has also found that depression and cognition are linked, with a possible strong link between depression and executive functioning. This study investigated how well baseline cerebrovascular burden and depression predicted verbal fluency three and six months later. This study also investigated if activity limitations increased the ability to predict long-term verbal fluency. Method. The sample included 139 medical rehabilitation patients, all at least 60 years of age. The Geriatric Depression Scale and Co-Morbidity Index (a measure of medical burden) were administered while patients were hospitalized. Participants were telephoned three and six months after discharge and were administered measures of verbal fluency (Controlled Oral Word Association [F and L] and Animal Naming) and a measure of activity limitations (the Instrumental Activities of Daily Living Scale). Structural equation modeling with maximum likelihood estimation was used to assess the ability of CVRFs, depression, and activity limitations to predict long-term verbal fluency, above and beyond demographic variables and medical burden. Results. Depression significantly predicted verbal fluency at both time points. CVRFs did not predict verbal fluency at any time point. Activity limitations were found to partially mediate the relationship between depression and verbal fluency at three months, and to completely mediate this relationship at six months. The structural equation models accounted for 43% of the variance in three-month verbal fluency and 60% of the variance in six-month verbal fluency. The structural equation models fit the data well, according to various fit indexes. Discussion. Findings suggest that etiological routes that lead to depression in older adults may also be related to long-term impairment in processing speed and other areas of cognition. Results also suggest a long-term process whereby depression may limit one's activities, which is related to poorer cognitive functioning. Lastly, results suggest that theories testing relationships between brain-based biological variables and cognition should include measurement of current functioning as well.

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