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Background: Episodic memory decline characterizes "normal" aging but is also a core symptom of Alzheimer's disease. Therefore, considerable efforts have been undertaken to study this memory domain and its neural substrates. Recent studies have mainly focused on encoding‐ and retrieval‐ related processes. However, some findings suggest that episodic memory deficits are at least in part due to impaired consolidation processes. Methods: We investigated age effects on consolidation‐related functional network changes and their vulnerability to cognitive interference, using fMRI data of 13 young (20–30 years) and 16 senior (49–75 years) participants. FMRI scanning was performed prior to and during a spatial memory paradigm, consisting of encoding, consolidation, and retrieval phases. To ensure that the observed connectivity changes were due to consolidation processes, the consolidation phase was manipulated over two sessions: (1) no manipulation and (2) repeated stimulus‐presentation with interfering spatial context information. Results: We compared the fractional amplitude of low‐frequency fluctuations (fALFF) to analyze spontaneous brain activity changes from pre‐ to post‐encoding rest. In the control condition, fALFF decreased within left supramarginal gyrus (SMG), right middle temporal gyrus (MTL), and left precuneus (Pc), whereas, fALFF increased within parts of the occipital and inferior temporal cortex. To evaluate the integration in large‐scale brain networks, connectivity analyses between the fALFF‐derived seeds and network ROIs were performed. We observed significant coupling between consolidation‐related brain regions and large‐scale brain networks during consolidation, with connectivity between the SMG and large parts of the memory network modulated by aging. There was also a disruptive effect of interference on connectivity between the Pc and parts of the salience network. Of particular importance for successful consolidation, however, is the connectivity between parts of the occipital lobe, the inferior and middle temporal gyrus. Connectivity within this network, which corresponds to the ventral visual stream, may predict subsequent memory performance. The predictive value appears to be higher in young than in seniors. Conclusion: Our results support the assumption that age‐related memory decline is at least partly caused by impaired consolidation processes. We showed that consolidation requires a complex interplay between large‐scale brain networks, which is partially disrupted by aging and thus becomes insufficient. [ABSTRACT FROM AUTHOR]

Background: In the last years, several voxel‐wise data‐driven metrics gained attention to study resting‐state connectivity in healthy aging and various pathological states. More recently, a new measure assessing the interaction between the commonly used metrics has been proposed and made widely available via the DPABI toolbox: the so‐called concordance index (CI). This index reflects the coupling of different metrics. The value of this new measure in Alzheimer's disease (AD) research is yet unclear. Method: Healthy young controls (YC, n=26), healthy senior controls (SC, n=29), and patients diagnosed with AD (n=35) underwent 3T resting‐state fMRI. First, the fractional amplitude of low frequency fluctuations (fALFF), regional homogeneity (ReHo), and degree centrality (DC) were calculated. Next, the CI among these measures was determined for each time window and each brain voxel across time by using Kendall's W. Differences in the CI between groups were examined on a whole brain, voxel‐wise, and network‐level using masks of seven of the most prominent intrinsic brain networks, with age, sex, head motion and gray matter volume as covariates. Result: The whole‐brain CI was significantly lower in AD patients as compared to YC and SC, which is in line with results from analyzing the single metrics. Reductions of the CI in AD was consistently observed in all networks investigated except for the limbic network. In SC compared to YC, no network‐level CI differences were detectable. On the voxel level, AD patients compared to SC showed lower CI in the right middle temporal gyrus, and SC compared to YC revealed lower CI in the left middle frontal gyrus. Analyzing the single metrics for their own, we observed a lower fALFF in the right angular gyrus in AD compared to SC, but no differences were detected for ReHo and DC. Conclusion: The newly proposed CI based on resting‐state connectivity may serve as a more sensitive imaging marker in AD than single metrics. The data suggest that this index distinguishes well between neurodegeneration and healthy aging. [ABSTRACT FROM AUTHOR]

Background: To date, it remains unclear how the hallmark pathological changes of Alzheimer's disease (AD), amyloid plaques, and neurofibrillary tangles, affect neuronal activity and, consequently, cognition. In cognitively normal aging, it appears that tau accumulation may drive hippocampal hyperactivity, however, studies investigating this association in AD are sparse. Method: Patients with mild cognitive impairment (MCI) or mild dementia due to AD (n = 15) underwent positron emission tomography with the tracer [18F]‐AV‐1451, which binds to tau accumulation, and performed a visual item memory task during functional magnetic resonance imaging. Result: Entorhinal tau accumulation was highly correlated with memory‐related hippocampal activation. Greater tau accumulation and hippocampal activation were negatively correlated with memory performance. Neural activation in other task‐related structures was not correlated with local or global tau accumulation. Conclusion: Similar to observations in cognitively healthy aging, entorhinal tau accumulation is closely associated with hippocampal hyperactivity and impaired memory performance in MCI and mild dementia. Interestingly, this association is specific for medial temporal lobe structures. [ABSTRACT FROM AUTHOR]