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Background: Many methods were developed to assess the functional intervoxel connectivity to better understand the brain function in individuals. In this study, k‐core percolation method was assessed to reveal the dynamic hierarchical structure on resting‐state fMRI (rsfMRI) on voxel‐level and the feasibility of the method was evaluated by applying it in the aging process. Method: Total 150 individuals were included in this study; 38 young healthy individuals from Seoul National University (SNU), and 32 aged healthy, 22 mild cognitive impairment‐converter (MCI‐C), 26 mild cognitive impairment non‐converter (MCI‐NC), and 32 Alzheimer's disease (AD) subjects from Alzheimer's Disease Neuroimaging Initiative (ADNI) database. K‐core percolation method, a voxel‐based approach was applied to reveal the hierarchical structure of voxels in the brain. kmax‐core and coreness k values derived from k‐core percolation characterizing the time‐varying core voxels were visualized on various plots to display the dynamic hierarchical structure more intuitively. Analysis was done in both static, dynamic studies, and in positive, negative correlations. Coreness k value map on brain T1 MRI was generated for further evaluation of the distribution of coreness k values. Result: Dynamic hierarchical structure of voxels on various plots revealed time‐varying change of kmax‐core voxels and coreness k values, reflecting the dynamic change of brain function in an individual, which was not fully reflected on static study. Dynamic flow pattern was different in positive and negative correlations, portraying the dynamic brain function in different neuronal networks. Asymmetric, unsynchronized distribution was deteriorated in the aging process on corneas k map and the asymmetry indexes of coreness k values revealed distinctive difference between young and aged healthy groups. The difference was more evident on dynamic study than static study. Also, as the age increased, coreness k values decreased, representing decreased connectivity in aging. However, asymmetry and decrease of coreness k values were not deteriorated by the severity of cognitive impairment. Conclusion: Investigation of dynamic functional connectivity with k‐core percolation on voxel‐level revealed time‐varying change of hierarchical structure of voxels in the aging process. With this method, characteristics of dynamic hierarchical structure of an individual can be discovered and have shown possibility of further clinical application. [ABSTRACT FROM AUTHOR]

Extracellular vesicles (EVs) are secreted nano‐sized vesicles that contain cellular proteins, lipids, and nucleic acids. Although EVs are expected to be biologically diverse, current analyses cannot adequately characterize this diversity because most are ensemble methods that inevitably average out information from diverse EVs. Here we describe a single vesicle analysis, which directly visualizes marker expressions of individual EVs using a total internal‐reflection microscopy and analyzes their co‐localization to investigate EV subpopulations. The single‐vesicle imaging and co‐localization analysis successfully illustrated the diversity of EVs and revealed distinct patterns of tetraspanin expressions. Application of the analysis demonstrated similarities and dissimilarities between the EV fractions that had been acquired from different conventional EV isolation methods. The analysis method developed in this study will provide a new and reliable tool for investigating characteristics of single EVs, and the findings of the analysis might increase understanding of the characteristics of EVs. [ABSTRACT FROM AUTHOR]

Finding underlying relationships among multiple imaging modalities in a coherent fashion is one of the challenging problems in multimodal analysis. In this study, we propose a novel approach based on multidimensional persistence. In the extension of the previous threshold-free method of persistent homology, we visualize and discriminate the topological change of integrated brain networks by varying not only threshold but also mixing ratio between two different imaging modalities. The multidimensional persistence is implemented by a new bimodal integration method called 1D projection. When the mixing ratio is predefined, it constructs an integrated edge weight matrix by projecting two different connectivity information onto the one dimensional shared space. We applied the proposed methods to PET and MRI data from 23 attention deficit hyperactivity disorder (ADHD) children, 21 autism spectrum disorder (ASD), and 10 pediatric control subjects. From the results, we found that the brain networks of ASD, ADHD children and controls differ, with ASD and ADHD showing asymmetrical changes of connected structures between metabolic and morphological connectivities. The difference of connected structure between ASD and the controls was mainly observed in the metabolic connectivity. However, ADHD showed the maximum difference when two connectivity information were integrated with the ratio 0.6. These results provide a multidimensional homological understanding of disease-related PET and MRI networks that disclose the network association with ASD and ADHD. Hum Brain Mapp 38:1387-1402, 2017. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In our daily lives, we are confronted with a large amount of information. Because only a small fraction can be encoded in long-term memory, the brain must rely on powerful mechanisms to filter out irrelevant information. To understand the neuronal mechanisms underlying the gating of information into long-term memory, we employed a paradigm where the encoding was directed by a 'Remember' or a 'No-Remember' cue. We found that posterior alpha activity increased prior to the 'No-Remember' stimuli, whereas it decreased prior to the 'Remember' stimuli. The sources were localized in the parietal cortex included in the dorsal attention network. Subjects with a larger cue-modulation of the alpha activity had better memory for the to-be-remembered items. Interestingly, alpha activity reflecting successful inhibition following the 'No-Remember' cue was observed in the frontal midline structures suggesting preparatory inhibition was mediated by anterior parts of the dorsal attention network. During the presentation of the memory items, there was more gamma activity for the 'Remember' compared to the 'No-Remember' items in the same regions. Importantly, the anticipatory alpha power during cue predicted the gamma power during item. Our findings suggest that top-down controlled alpha activity reflects attentional inhibition of sensory processing in the dorsal attention network, which then finally gates information to long-term memory. This gating is achieved by inhibiting the processing of visual information reflected by neuronal synchronization in the gamma band. In conclusion, the functional architecture revealed by region-specific changes in the alpha activity reflects attentional modulation which has consequences for long-term memory encoding. Hum Brain Mapp 35:3972-3987, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Three diketopiperazines (Ia), (Ib), and (Ic) are isolated from two strains of marine-derived bacteria. [ABSTRACT FROM AUTHOR]