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191 Publications

Showing 81-90 of 191 results
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    07/01/19 | Effective dimensionality reduction for visualizing neural dynamics by laplacian eigenmaps.
    Sun G, Zhang S, Zhang Y, Xu K, Zhang Q, Zhao T, Zheng X
    Neural Computation. 2019 Jul;31(7):1356-1379. doi: 10.1162/neco_a_01203

    With the development of neural recording technology, it has become possible to collect activities from hundreds or even thousands of neurons simultaneously. Visualization of neural population dynamics can help neuroscientists analyze large-scale neural activities efficiently. In this letter, Laplacian eigenmaps is applied to this task for the first time, and the experimental results show that the proposed method significantly outperforms the commonly used methods. This finding was confirmed by the systematic evaluation using nonhuman primate data, which contained the complex dynamics well suited for testing. According to our results, Laplacian eigenmaps is better than the other methods in various ways and can clearly visualize interesting biological phenomena related to neural dynamics.

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    07/01/19 | Large scale image segmentation with structured loss based deep learning for connectome reconstruction.
    Funke J, Tschopp FD, Grisaitis W, Sheridan A, Singh C, Saalfeld S, Turaga SC
    IEEE Transactions on Pattern Analysis and Machine Intelligence. 2019 Jul 1;41(7):1669-80. doi: 10.1109/TPAMI.2018.2835450

    We present a method combining affinity prediction with region agglomeration, which improves significantly upon the state of the art of neuron segmentation from electron microscopy (EM) in accuracy and scalability. Our method consists of a 3D U-net, trained to predict affinities between voxels, followed by iterative region agglomeration. We train using a structured loss based on MALIS, encouraging topologically correct segmentations obtained from affinity thresholding. Our extension consists of two parts: First, we present a quasi-linear method to compute the loss gradient, improving over the original quadratic algorithm. Second, we compute the gradient in two separate passes to avoid spurious gradient contributions in early training stages. Our predictions are accurate enough that simple learning-free percentile-based agglomeration outperforms more involved methods used earlier on inferior predictions. We present results on three diverse EM datasets, achieving relative improvements over previous results of 27%, 15%, and 250%. Our findings suggest that a single method can be applied to both nearly isotropic block-face EM data and anisotropic serial sectioned EM data. The runtime of our method scales linearly with the size of the volume and achieves a throughput of ~2.6 seconds per megavoxel, qualifying our method for the processing of very large datasets.

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    07/01/19 | State-dependent decoupling of sensory and motor circuits underlies behavioral flexibility in Drosophila.
    Ache JM, Namiki S, Lee A, Branson K, Card GM
    Nature Neuroscience. 2019 Jul 01;22(7):1132-1139. doi: 10.1038/s41593-019-0413-4

    An approaching predator and self-motion toward an object can generate similar looming patterns on the retina, but these situations demand different rapid responses. How central circuits flexibly process visual cues to activate appropriate, fast motor pathways remains unclear. Here we identify two descending neuron (DN) types that control landing and contribute to visuomotor flexibility in Drosophila. For each, silencing impairs visually evoked landing, activation drives landing, and spike rate determines leg extension amplitude. Critically, visual responses of both DNs are severely attenuated during non-flight periods, effectively decoupling visual stimuli from the landing motor pathway when landing is inappropriate. The flight-dependence mechanism differs between DN types. Octopamine exposure mimics flight effects in one, whereas the other probably receives neuronal feedback from flight motor circuits. Thus, this sensorimotor flexibility arises from distinct mechanisms for gating action-specific descending pathways, such that sensory and motor networks are coupled or decoupled according to the behavioral state.

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    06/27/19 | A split fluorescent reporter with rapid and reversible complementation.
    Tebo AG, Gautier A
    Nature communications. 06/2019;10:2822. doi: 10.1038/s41467-019-10855-0

    Interactions between proteins play an essential role in metabolic and signaling pathways, cellular processes and organismal systems. We report the development of splitFAST, a fluorescence complementation system for the visualization of transient protein-protein interactions in living cells. Engineered from the fluorogenic reporter FAST (Fluorescence-Activating and absorption-Shifting Tag), which specifically and reversibly binds fluorogenic hydroxybenzylidene rhodanine (HBR) analogs, splitFAST displays rapid and reversible complementation, allowing the real-time visualization of both the formation and the dissociation of a protein assembly.

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    Looger LabAhrens Lab
    06/27/19 | Glia accumulate evidence that actions are futile and suppress unsuccessful behavior.
    Mu Y, Bennett DV, Rubinov M, Narayan S, Yang C, Tanimoto M, Mensh BD, Looger LL, Ahrens MB
    Cell. 2019 Jun 27;178(1):27-43. doi: 10.1016/j.cell.2019.05.050

    When a behavior repeatedly fails to achieve its goal, animals often give up and become passive, which can be strategic for preserving energy or regrouping between attempts. It is unknown how the brain identifies behavioral failures and mediates this behavioral-state switch. In larval zebrafish swimming in virtual reality, visual feedback can be withheld so that swim attempts fail to trigger expected visual flow. After tens of seconds of such motor futility, animals became passive for similar durations. Whole-brain calcium imaging revealed noradrenergic neurons that responded specifically to failed swim attempts and radial astrocytes whose calcium levels accumulated with increasing numbers of failed attempts. Using cell ablation and optogenetic or chemogenetic activation, we found that noradrenergic neurons progressively activated brainstem radial astrocytes, which then suppressed swimming. Thus, radial astrocytes perform a computation critical for behavior: they accumulate evidence that current actions are ineffective and consequently drive changes in behavioral states.

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    06/26/19 | High-dimensional geometry of population responses in visual cortex.
    Stringer C, Pachitariu M, Steinmetz NA, Carandini M, Harris KD
    Nature. 2019 Jun 26;571(7765):361-65. doi: 10.1038/s41586-019-1346-5

    A neuronal population encodes information most efficiently when its activity is uncorrelated and high-dimensional, and most robustly when its activity is correlated and lower-dimensional. Here, we analyzed the correlation structure of natural image coding, in large visual cortical populations recorded from awake mice. Evoked population activity was high dimensional, with correlations obeying an unexpected power-law: the n-th principal component variance scaled as 1/n. This was not inherited from the 1/f spectrum of natural images, because it persisted after stimulus whitening. We proved mathematically that the variance spectrum must decay at least this fast if a population code is smooth, i.e. if small changes in input cannot dominate population activity. The theory also predicts larger power-law exponents for lower-dimensional stimulus ensembles, which we validated experimentally. These results suggest that coding smoothness represents a fundamental constraint governing correlations in neural population codes.

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    06/27/19 | High-resolution imaging reveals how the spindle midzone impacts chromosome movement.
    Pamula MC, Carlini L, Forth S, Verma P, Suresh S, Legant WR, Khodjakov A, Betzig E, Kapoor TM
    The Journal of Cell Biology. 27 Jun 2019;218(8):2529-44. doi: 10.1083/jcb.201904169

    In the spindle midzone, microtubules from opposite half-spindles form bundles between segregating chromosomes. Microtubule bundles can either push or restrict chromosome movement during anaphase in different cellular contexts, but how these activities are achieved remains poorly understood. Here, we use high-resolution live-cell imaging to analyze individual microtubule bundles, growing filaments, and chromosome movement in dividing human cells. Within bundles, filament overlap length marked by the cross-linking protein PRC1 decreases during anaphase as chromosome segregation slows. Filament ends within microtubule bundles appear capped despite dynamic PRC1 turnover and submicrometer proximity to growing microtubules. Chromosome segregation distance and rate are increased in two human cell lines when microtubule bundle assembly is prevented via PRC1 knockdown. Upon expressing a mutant PRC1 with reduced microtubule affinity, bundles assemble but chromosome hypersegregation is still observed. We propose that microtubule overlap length reduction, typically linked to pushing forces generated within filament bundles, is needed to properly restrict spindle elongation and position chromosomes within daughter cells.

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    06/01/17 | Ensemble cryo-EM elucidates the mechanism of translation fidelity.
    Loveland AB, Demo G, Grigorieff N, Korostelev AA
    Nature. 2017 Jun 01;546(7656):113-117. doi: 10.1038/nature22397

    Gene translation depends on accurate decoding of mRNA, the structural mechanism of which remains poorly understood. Ribosomes decode mRNA codons by selecting cognate aminoacyl-tRNAs delivered by elongation factor Tu (EF-Tu). Here we present high-resolution structural ensembles of ribosomes with cognate or near-cognate aminoacyl-tRNAs delivered by EF-Tu. Both cognate and near-cognate tRNA anticodons explore the aminoacyl-tRNA-binding site (A site) of an open 30S subunit, while inactive EF-Tu is separated from the 50S subunit. A transient conformation of decoding-centre nucleotide G530 stabilizes the cognate codon-anticodon helix, initiating step-wise 'latching' of the decoding centre. The resulting closure of the 30S subunit docks EF-Tu at the sarcin-ricin loop of the 50S subunit, activating EF-Tu for GTP hydrolysis and enabling accommodation of the aminoacyl-tRNA. By contrast, near-cognate complexes fail to induce the G530 latch, thus favouring open 30S pre-accommodation intermediates with inactive EF-Tu. This work reveals long-sought structural differences between the pre-accommodation of cognate and near-cognate tRNAs that elucidate the mechanism of accurate decoding.

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    Svoboda Lab
    06/26/19 | Ephus: multipurpose data acquisition software for neuroscience experiments.
    Suter BA, O'Connor T, Iyer V, Petreanu LT, Hooks BM, Kiritani T, Svoboda K, Shepherd GM
    Front Neural Circuits. 2010;4:100. doi: 10.3389/fncir.2010.00100

    Physiological measurements in neuroscience experiments often involve complex stimulus paradigms and multiple data channels. Ephus (http://www.ephus.org) is an open-source software package designed for general-purpose data acquisition and instrument control. Ephus operates as a collection of modular programs, including an ephys program for standard whole-cell recording with single or multiple electrodes in typical electrophysiological experiments, and a mapper program for synaptic circuit mapping experiments involving laser scanning photostimulation based on glutamate uncaging or channelrhodopsin-2 excitation. Custom user functions allow user-extensibility at multiple levels, including on-line analysis and closed-loop experiments, where experimental parameters can be changed based on recently acquired data, such as during in vivo behavioral experiments. Ephus is compatible with a variety of data acquisition and imaging hardware. This paper describes the main features and modules of Ephus and their use in representative experimental applications.

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    01/04/18 | Genetics of intellectual disability in consanguineous families.
    Hu H, Kahrizi K, Musante L, Fattahi Z, Herwig R, Hosseini M, Oppitz C, Abedini SS, Suckow V, Larti F, Beheshtian M, Lipkowitz B, Akhtarkhavari T, Mehvari S, Otto S, Mohseni M, Arzhangi S, Jamali P, Mojahedi F, Taghdiri M, Papari E, Soltani Banavandi MJ, Akbari S, Tonekaboni SH, Dehghani H, Ebrahimpour MR, Bader I, Davarnia B, Cohen M, Khodaei H, Albrecht B, Azimi S, Zirn B, Bastami M, Wieczorek D, Bahrami G, Keleman K, Vahid LN, Tzschach A, Gärtner J, Gillessen-Kaesbach G, Varaghchi JR, Timmermann B, Pourfatemi F, Jankhah A, Chen W, Nikuei P, Kalscheuer VM, Oladnabi M, Wienker TF, Ropers H, Najmabadi H
    Mol Psychiatry. 2018 Jan 04;24(7):1027-1039. doi: 10.1038/s41380-017-0012-2

    Autosomal recessive (AR) gene defects are the leading genetic cause of intellectual disability (ID) in countries with frequent parental consanguinity, which account for about 1/7th of the world population. Yet, compared to autosomal dominant de novo mutations, which are the predominant cause of ID in Western countries, the identification of AR-ID genes has lagged behind. Here, we report on whole exome and whole genome sequencing in 404 consanguineous predominantly Iranian families with two or more affected offspring. In 219 of these, we found likely causative variants, involving 77 known and 77 novel AR-ID (candidate) genes, 21 X-linked genes, as well as 9 genes previously implicated in diseases other than ID. This study, the largest of its kind published to date, illustrates that high-throughput DNA sequencing in consanguineous families is a superior strategy for elucidating the thousands of hitherto unknown gene defects underlying AR-ID, and it sheds light on their prevalence.

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