Functional Correlates Of Verbal Working Memory In Healthy Aging And Early Alzheimer\u27s Disease

Deficits in the working memory system are common in patients diagnosed with Alzheimer\u27s disease (AD). However, little is known regarding the neurobiological basis of this impairment. The current study examined the neurobiological functional correlates of the working memory system in early AD patients and cognitively intact control participants using a word list repetition task performed during positron emission tomography (PET). Compared to a reading control task, both the AD and control groups utilized a network of parietal, frontal, and cerebellar regions while completing the word rehearsal task. However, control participants displayed greater activation in all regions, especially in the parietal lobes. In the frontal lobes, AD patients displayed right-lateralized recruitment compared to bilateral frontal recruitment in the control group. Comparison of 10-word list rehearsal to 5-word indicated a shift from parietal activity to more prominent frontal and cerebellar activity in the control group with increased load demands. This type of shift in activity was not observed in the patient group. Additionally, parietal activity was inversely correlated with working memory performance in the control group only. Left cerebellar activity was correlated with behavioral performance in both groups. Overall, it appears that the working memory deficits observed in AD patients may be related to dysfunction in parietal contributions to the working memory network, and compensatory activity may occur in the frontal lobes