Editors' Choice

Science  20 Oct 2017:
Vol. 358, Issue 6361, pp. 317
  1. Cognitive Science

    A hammer is a hammer is a hammer

    1. Gilbert Chin

    Children begin to understand the difference between institutional objects (such as money) and standard artifacts (such as hammers) at a young age.

    PHOTO: ISTOCK.COM/DANCHOOALEX

    Hammers are designed to strike other objects, such as a nail or a rivet. A hammer's use is independent of cultural norms or social agreements, in contrast to money, whose value and function as a medium of exchange very much relies on a common understanding, which can change when the consensus changes. Noyes et al. show that young children begin to grasp the difference between what the authors refer to as institutional (socially dependent) objects and standard artifacts, such as hammers and chairs, between the ages of 4 and 9 years.

    Cognition 10.1016/j.cognition.2017.09.008 (2017).

  2. Epilepsy

    Small groups influence large networks

    1. Peter Stern

    How small groups of neurons can interact with large networks in the brain is a crucial question in epilepsy research. Eissa et al. analyzed multielectrode array recordings from epileptic patients and found that during seizures, local action-potential activity organized into tiny wave fronts that correlated with network activity on scales that were orders of magnitude larger. These correlations did not exist between seizures or in neuronal activity outside the wave front. Computational modeling revealed an antagonistic role for feedforward inhibition. At the local level, inhibition failed, which permitted the wave front to propagate. In contrast, at a much larger scale, feedforward inhibition created the conditions for the seizure to cease after the wave front had vanished.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1702490114 (2017).

  3. Cell Biology

    PolyQ caught in the act?

    1. Stella M. Hurtley

    Huntington's disease is a neurodegenerative disorder caused by the expanded polyglutamine (polyQ) repeat of mutant huntingtin (mHtt). PolyQ expansions result in protein aggregation into large neuronal inclusion bodies (IBs). These IBs are often regarded as protective deposits of toxic soluble species. Bäuerlein et al. used cryo-electron tomography to analyze the structure of mHtt IBs in mammalian cells and neurons under close-to-native conditions and at molecular resolution. The mHtt IBs consisted of radially arranged fibrils that closely interacted with cellular endomembranes, particularly the endoplasmic reticulum (ER). The interaction appeared to alter ER function and membrane dynamics at the IB periphery. Thus, rather than being inert deposits, mHtt IBs may mediate aspects of polyQ pathology.

    Cell 171, 179 (2017).

  4. Marine Geology

    Sorting out submarine canyons

    1. Brent Grocholski

    Monterey Canyon, CA. Bedrock type and sediment flux are the most important factors explaining the location of submarine canyons.

    CREDIT: GOOGLE; (DATA) CSUMB SFML, CA OPC, MBARI, LDEO-COLUMBIA, NSF, NOAA, SIO, NOAA, U.S. NAVY, NGA, GEBCO

    Submarine canyons, often found directly off the coastline, are common but understudied features of Earth. Despite their prevalence, what determines their location and morphology remains a mystery. Smith et al. used a massive data set from the entire western coast of the United States to determine what variables best correlated with underwater canyon formation. They found that the distribution of rock type and sediment flux were the most important factors for explaining the location of submarine canyons.

    Geophys. Res. Lett. 10.1002/2017GL075139 (2017).

  5. Nonlinear Systems

    Causal interactions in dynamical systems

    1. Peter Stern

    Classically, causality requires that state A has independent information that influences state B. If this happens only in one direction, A is said to causally act on B. In nonlinear dynamical systems, however, interactions are mutual. Their parts cannot be separated in this simple way. A definition of causal efficacy that generalizes the classical unidirectional (“acyclic”) notion of causality to the nonseparable bidirectional (“cyclic”) case is missing. Harnack et al. propose a mathematically transparent definition of effective causal influences in cyclic dynamical systems. This relies on reconstructions of the system's overall state from measurements. Reconstructions are obtained in parallel from observations at different system components. Although generally the respective reconstructions are topologically equivalent, the mapping among the reconstructions exhibits distortions that reflect effective causal influences.

    Phys. Rev. Lett. 119, 098301 (2017).

  6. Immunology

    Notch signaling schools thymic DCs

    1. Seth Thomas Scanlon

    Conventional and plasmacytoid dendritic cells in the thymus are important for the establishment of central tolerance. They induce autoreactive T cell death and generate regulatory T cells. Although these cells are believed to have an extrathymic origin, Martín-Gayo et al. uncovered evidence that human early thymic progenitors (ETPs) are another source. From postnatal thymocytes, ETPs differentiate into CD123+ common dendritic cell progenitors that can reconstitute dendritic cells in immunodeficient murine thymi. JAG1-mediated Notch signaling in medullary niches is critical for this process. The idea is that thymic progenitors, which escape strong Notch signaling via ligands such as DLL1 and DLL4 and then encounter JAG1, become myeloid-primed by up-regulating GATA2 and turning off GATA3.

    J. Exp. Med. 10.1084/jem.20161564 (2017).

  7. Political Science

    The internet and political polarization

    1. Barbara R. Jasny

    Many commentators have discussed the increase in political polarization in the United States and have blamed it on the internet and social media. Boxell et al. used data from the American National Election Studies and the Pew Research Center to look at demographic changes in polarization between 1996 and 2016. Unsurprisingly, younger people adopted the internet and social media much faster than the elderly. However, by several measures, those older than 65 increased more in polarization between 1996 and 2016 than those aged 18 to 39. Thus, for reasons still not fully understood, the people who tend to use internet and social media the least have undergone the highest increase in polarization.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1706588114 (2017).