Abnormal Functional Connectivity of Thalamic Subdivisions in Alzheimer’s Disease: A Functional Magnetic Resonance Imaging Study
Yue WuXingqi WuLiying GaoYibing YanZhi GengShanshan ZhouWanqiu ZhuYanghua TianYongqiang YuLing WeiKai Wang
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Cognitive deficit
To review the role of the precuneus in major depression We will review the literature involving the precuneus in the pathophysiology of depression. We will also report a recent study of our group using structural MRI and VBM analyses to assess the role of precuneus in Autobiographical Memory (AM). Visual perspective during AM retrieval was assessed in two independent datasets of 45 and 20 healthy young adults with two different AM retrieval tasks. Precuneus, a medial part of the parietal cortex, is a central component of the default mode network. Results from our VBM study show that the precuneus volume in healthy subjects is correlated with the ability to retrieve autobiographical memories with a first-person perspective. Consistent with its role in integration of self-relevant mental simulations with past experiences and visuo-spatial processes during AM retrieval, the precuneus may subserve emotion regulation processes in healthy subjects and depressed patients. The precuneus and the default mode network show abnormal connectivity in depressed patients that may indicate abnormal self-processing in depression. Abnormal activity and connectivity of the precuneus within the default mode network is associated with impairment in self-processing in depression and may be related to the tendency of depressed patients to retrieve AM using third-person perspective. Further studies are needed to evaluate if impaired function or structure of the precuneus may predict the clinical response to antidepressant treatment.
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Abstract Activation of parietal cortex structures like the precuneus is commonly observed during explicit memory retrieval, but the role of parietal cortices in encoding has only recently been appreciated and is still poorly understood. Considering the importance of the precuneus in human visual attention and imagery, we aimed to assess a potential role for the precuneus in the encoding of visuospatial representations into long‐term memory. We therefore investigated the acquisition of constant versus repeatedly shuffled configurations of icons on background images over five subsequent days in 32 young, healthy volunteers. Functional magnetic resonance imaging was conducted on Days 1, 2, and 5, and persistent memory traces were assessed by a delayed memory test after another 5 days. Constant compared to shuffled configurations were associated with significant improvement of position recognition from Day 1 to 5 and better delayed memory performance. Bilateral dorsal precuneus activations separated constant from shuffled configurations from Day 2 onward, and coactivation of the precuneus and hippocampus dissociated recognized and forgotten configurations, irrespective of condition. Furthermore, learning of constant configurations elicited increased functional coupling of the precuneus with dorsal and ventral visual stream structures. Our results identify the precuneus as a key brain structure in the acquisition of detailed visuospatial information by orchestrating a parieto–occipito–temporal network.
Superior parietal lobule
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Cognitive impairment is common after head injury, even when the injury has been minor and does not require inpatient assessment or management. The intellectual deficit is maximal in the first week after injury and tends to resolve spontaneously within three or four weeks. It may, however, still be present six months or longer after the injury. Neuropsychologic testing is required to detect subtle cognitive deficits that may nevertheless have far-reaching effects. Cognitive impairment after head injury has specific implications for family physicians, team physicians, educators and athletic coaches.
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Posterior cingulate
Cingulate cortex
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The precuneus/posterior cingulate (PCC) is a hub region of the default-mode network (DMN) and a prominent target of amyloid-beta (Aß) deposition in MCI and AD causing subsequent disruptions of DMN functional connectivity (FC). In subjective cognitive decline (SCD), amyloid load effects on posterior DMN FC are less well known. We aimed to compare precuneus FC in SCD with and without amyloid deposition and to disentangle the contributions of regional & global Aß load. We included age and sex-matched 24 SCDAß+ and 22 SCDAß- individuals from the DELCODE-PET sub-cohort (Tab. 1), based on qualitative ratings of [18F]florbetaben (Neuraceq™) PET scans by two experienced readers. Global and regional amyloid burden was quantified by standard uptake value ratios (SUVR) using cerebellar cortex as reference region. Resting-state fMRI data were acquired at 3T, and preprocessed and analyzed with DPARSFA. Seed-based FC maps were generated between the time series of a bilateral precuneus seed region and each voxel of the whole brain, respectively. Voxelwise FC group differences in two-sample t-tests were considered significant at p < 0.005 voxel-level and p < 0.05 FWE cluster-level. For clusters showing significant group differences, follow-up analyses explored correlations between their mean FC values and (i) regional PCC amyloid load and (ii) global amyloid load. Precuneus FC was significantly increased with occipital and lingual/cerebellar regions, and significantly decreased with left superior/middle frontal and left inferior parietal / angular regions in SCDAß+ as compared to SCDAß (Tab.2, Fig.1). In the SCDAß+ group only, precuneus-occipital mean FC showed a significant positive correlation with PCC amyloid load (r=0.42, p=0.04) (Fig.2).
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Amyloid (mycology)
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Interactions between the thalamus and the cortex play an important role in consciousness. The thalamus as a homogenous structure is less strongly connected with the default mode network (DMN) in patients with disorders of consciousness (DOC), but the roles of specific thalamic nuclei are not clear. The purpose of this study was to investigate the functional connectivity between individual thalamic nuclei and the DMN in DOC patients.Nine DOC patients and nine age-matched healthy controls were scanned with functional magnetic resonance imaging (fMRI) at resting state. Data-driven independent component analysis and hypothesis-driven region of interest-based correlation analysis were performed.In comparison with healthy controls, DOC patients had significantly decreased functional connectivity between the mediodorsal thalamus and brain areas within the DMN, including the medial prefrontal cortex and posterior cingulate cortex/precuneus. Patients and controls did not show significant differences in functional connectivity in other thalamic nuclei.Our results suggest that functional connections between the mediodorsal thalamus and the DMN may play important roles in the pathogenesis of DOC.
Persistent vegetative state
Consciousness Disorders
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Homo sapiens
Human Connectome Project
Human brain
Brain morphometry
Animal ecology
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Posterior cingulate
Inferior parietal lobule
Superior parietal lobule
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Functional MRI studies involving the precuneus, a region in the posterior of the brain, reveal what may be a new way to distinguish patients with mild cognitive impairment (MCI) from those with Alzheimer’s disease.
Posterior cingulate
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Cognitive deficit
Motor impairment
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