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- Johansson, Jarkko, et al.
(författare)
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Longitudinal evidence that reduced hemispheric encoding/retrieval asymmetry predicts episodic-memory impairment in aging
- 2020
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Ingår i: Neuropsychologia. - : Elsevier BV. - 0028-3932 .- 1873-3514. ; 137
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Tidskriftsartikel (refereegranskat)abstract
- The HERA (Hemispheric Encoding/Retrieval Asymmetry) model captures hemispheric lateralization of prefrontal cortex (PFC) brain activity during memory encoding and retrieval. Reduced HERA has been observed in cross-sectional aging studies, but there is no longitudinal evidence, to our knowledge, on age-related changes in HERA and whether maintained or reduced HERA relates to well-preserved memory functioning. In the present study we set out to explore HERA in a longitudinal neuroimaging sample from the Betula study [3 Waves over 10 years; Wave-1: n = 363, W2: n = 227, W3: n = 101]. We used fMRI data from a face-name paired-associates task to derive a HERA index. In support of the HERA model, the mean HERA index was positive across the three imaging waves. The longitudinal age-HERA relationship was highly significant (p < 10(-11)), with a HERA decline occurring after age 60. The age-related HERA decline was associated with episodic memory decline (p < 0.05). Taken together, the findings provide large-scale support for the HERA model, and suggest that reduced HERA in the PFC reflects pathological memory aging possibly related to impaired ability to bias mnemonic processing according to the appropriate encoding or retrieval state.
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| 2. |
- Nyberg, Lars, 1966-, et al.
(författare)
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Frontal Contribution to Hippocampal Hyperactivity During Memory Encoding in Aging
- 2019
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Ingår i: Frontiers in Molecular Neuroscience. - : Frontiers Media S.A.. - 1662-5099. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Hippocampal hypo- as well as hyper-activation have been reported during memory encoding in older individuals. Prefrontal cortex (PFC) provides top-down state signals to the hippocampus that bias its computation during memory encoding and retrieval, and disturbed top-down signals could contribute to hippocampal hyper-activation. Here, we used >500 cross-sectional and longitudinal observations from a face-name encoding-retrieval fMRI task to examine hippocampal hypo-and hyper-activation in aging. Age-related anterior hippocampal hypo-activation was observed during memory encoding. Next, older individuals who longitudinally dropped-out were compared with those who remained in the study. Older dropouts had lower memory performance and higher dementia risk, and hyper-activated right anterior and posterior hippocampus during memory encoding. During encoding, the dropouts also activated right prefrontal regions that instead were active during retrieval in younger and older remainers. Moreover, the dropouts showed altered frontal-hippocampal functional connectivity, notably elevated right PFC to anterior hippocampus (aHC) connectivity during encoding. In the context of a general pattern of age-related anterior hippocampal hypo-activation during encoding, these findings support a top-down contribution to paradoxically high anterior hippocampal activity in older dropouts who were at elevated risk of pathology.
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| 3. |
- Gorbach, Tetiana, 1991-, et al.
(författare)
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A Hierarchical Bayesian Mixture Model Approach for Analysis of Resting-State Functional Brain Connectivity : An Alternative to Thresholding
- 2020
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Ingår i: Brain Connectivity. - : Mary Ann Liebert. - 2158-0014 .- 2158-0022. ; 10:5, s. 202-211
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Tidskriftsartikel (refereegranskat)abstract
- This article proposes a Bayesian hierarchical mixture model to analyze functional brain connectivity where mixture components represent "positively connected" and "non-connected" brain regions. Such an approach provides a data-informed separation of reliable and spurious connections in contrast to arbitrary thresholding of a connectivity matrix. The hierarchical structure of the model allows simultaneous inferences for the entire population as well as for each individual subject. A new connectivity measure, the posterior probability of a given pair of brain regions of a specific subject to be connected given the observed correlation of regions' activity, can be computed from the model fit. The posterior probability reflects the connectivity of a pair of regions relative to the overall connectivity pattern of an individual, which is overlooked in traditional correlation analyses. This article demonstrates that using the posterior probability might diminish the effect of spurious connections on inferences, which is present when a correlation is used as a connectivity measure. In addition, simulation analyses reveal that the sparsification of the connectivity matrix using the posterior probabilities might outperform the absolute thresholding based on correlations. Therefore, we suggest that posterior probability might be a beneficial measure of connectivity compared with the correlation. The applicability of the introduced method is exemplified by a study of functional resting-state brain connectivity in older adults.
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| 6. |
- Salami, Alireza, et al.
(författare)
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Association of APOE ɛ4 and Plasma p-tau181 with Preclinical Alzheimer’s Disease and Longitudinal Change in Hippocampus Function
- 2022
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Ingår i: Journal of Alzheimer's Disease. - : IOS Press. - 1387-2877 .- 1875-8908. ; 85:3, s. 1309-1320
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Apolipoprotein E (APOE) ɛ4 allele has been linked to increased tau phosphorylation and tangle formation. APOE ɛ4 carriers with elevated tau might be at the higher risk for Alzheimer’s disease (AD) progression. Previous studies showed that tau pathology begins early in areas of the medial temporal lobe. Similarly, APOE ɛ4 carriers showed altered hippocampal functional integrity. However, it remains unknown whether the influence of elevated tau accumulation on hippocampal functional changes would be more pronounced for APOE ɛ4 carriers.Objective: We related ɛ4 carriage to levels of plasma phosphorylated tau (p-tau181) up to 15 years prior to AD onset. Furthermore, elevated p-tau181 was explored in relation to longitudinal changes in hippocampal function and connectivity.Methods: Plasma p-tau181 was analyzed in 142 clinically defined AD cases and 126 matched controls. The longitudinal analysis involved 87 non-demented individuals (from population-based study) with two waves of plasma samples and three waves of functional magnetic resonance imaging during rest and memory encoding.Results: Increased p-tau181 was observed for both ɛ4 carriers and non-carriers close to AD onset, but exclusively for ɛ4 carriers in the early preclinical groups (7- and 13-years pre-AD). In ɛ4 carriers, longitudinal p-tau181 increase was paralleled by elevated local hippocampal connectivity at rest and subsequent reduction of hippocampus encoding-related activity.Conclusion: Our findings support an association of APOE ɛ4 and p-tau181 with preclinical AD and hippocampus functioning.
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