Early functional network alterations in asymptomatic elders at risk for Alzheimer's disease.

Amyloid-ß (Aß) deposition is known to starts decades before the onset of clinical symptoms of Alzheimer's disease (AD), however, the detailed pathophysiological processes underlying this preclinical period are not well understood. This study aimed to investigate functional network alterations in cognitively intact elderly individuals at risk for AD, and assessed the association between these network alterations and changes in Aß deposition, glucose metabolism, and brain structure. Forty-five cognitively normal elderly subjects, who were classified into Aß-positive (CN+) and Aß-negative (CN-) groups using 11C-Pittsburgh compound B PET, underwent resting state magnetoencephalography measurements, 18F-fluorodeoxyglucose PET (FDG-PET) and structural MRI. Results demonstrated that in the CN+ group, functional connectivity (FC) within the precuneus was significantly decreased, whereas it was significantly enhanced between the precuneus and the bilateral inferior parietal lobules in the low-frequency bands (theta and delta). These changes were suggested to be associated with local cerebral Aß deposition. Most of Aß+ individuals in this study did not show any metabolic or anatomical changes, and there were no significant correlations between FC values and FDG-PET or MRI volumetry data. These results demonstrate that functional network alterations, which occur in association with Aß deposition, are detectable using magnetoencephalography before metabolic and anatomical changes are seen.

Age-Related Changes in Attentional Control Using an N-Back Working Memory Paradigm.

BACKGROUND/STUDY CONTEXT: Older adults tend to be affected by task-irrelevant distracters. However, whether or not this aging effect is evident when task-irrelevant and relevant stimuli are presented across different sensory modalities is still a subject of debate. The purpose of the present study was to clarify age-related differences in the effects of auditory distraction on visual information processing. METHODS: Participants included 20 young individuals, 20 younger-old individuals in their 60s, and 20 older-old individuals in their 70s. Visual n-back (1-back, 2-back) working memory (WM) tasks using Japanese words were examined with and without auditory distracter conditions. Participants' performances were analyzed using a three-way analysis of variance: 3 (age group) × 2 (distraction) × 2 (working memory load). RESULTS: The effects of auditory distractions were influenced by aging and WM load. Auditory distractions disturbed WM performances preferentially in older adults. Further, participants in the older-old group were more affected by auditory distractions than those in the younger-old group, especially during the 2-back task. CONCLUSION: These results suggested that the WM performances for visual n-back tasks were largely disturbed by auditory distractions in older adults but not in young adults.