Abstract
Functional imaging studies consistently find that older adults recruit bilateral brain regions in cognitive tasks that are strongly lateralized in younger adults, a characterization known as the Hemispheric Asymmetry Reduction in Older Adults model. While functional imaging displays what brain areas are active during tasks, it cannot demonstrate what brain regions are necessary for task performance. We used behavioral data from acute stroke patients to test the hypothesis that older adults need both hemispheres for a verbal working memory task that is predominantly left-lateralized in younger adults. Right-handed younger (age ≥ 50,n= 7) and older adults (age > 50,n= 21) with acute unilateral stroke, as well as younger (n= 6) and older (n= 13) transient ischemic attack (TIA) patients, performed a self-paced verbal item-recognition task. Older patients with stroke to either hemisphere had a higher frequency of deficits in the verbal working memory task compared to older TIA patients. Additionally, the deficits in older stroke patients were mainly in retrieval time while the deficits in younger stroke patients were mainly in accuracy. These data suggest that bihemispheric activity is necessary for older adults to successfully perform a verbal working memory task.
Highlights
Functional imaging is a valuable tool in measuring brain activity during cognitive processes in humans
Age ranged from 38–79 years (57.17 ± 2.1; mean and SEM) for stroke patients and 21–84 years (56.89 ± 3.5) for transient ischemic attack (TIA) patients
A two-sample t-test comparing education levels between groups revealed that older stroke patients had a trend of having more years of education compared to older TIA patients (t(13) = 2.0, p = 0.066)
Summary
Functional imaging is a valuable tool in measuring brain activity during cognitive processes in humans. It is important to validate results obtained from functional imaging studies, and one way to do so in humans is with lesion studies [31,41]. Lesion effects can be studied in stroke patients. Chronic stroke patients have been studied extensively to test the necessity of the affected area for many cognitive tasks, including working memory [for review, see [31]]. While studies of chronic stroke patients can provide valuable information, one drawback is that considerable reorganization is known to occur over time [38,53]. The use of acute stroke patients provides the unique opportunity to test the effect of the lesion on performance before substantial reorganization can occur. Diffusion-weighted imaging (DWI) and perfusion weighted imaging (PWI) can be used to
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