Catálogo de publicaciones - revistas

<jats:title>Wiring the Retina</jats:title> <jats:p> Starburst amacrine cells in the retina detect motion by responding to light going on or off. <jats:bold> L. O. Sun <jats:italic>et al.</jats:italic> </jats:bold> ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.1241974">10.1126/science.1241974</jats:related-article> ) analyzed how the cellular circuits develop in the mouse retina to form the basis of motion detection. Expression patterns of semaphorin 6A and its receptor plexin A2 defined the shape and reactivity of the starburst amacrine cells. Semaphorin 6A expression was restricted to particular cells, generating two classes of starburst amacrine cells with distinct morphologies and opposing functions. </jats:p>

<jats:p>Small-world networks provide an appealing description of cortical architecture owing to their capacity for integration and segregation combined with an economy of connectivity. Previous reports of low-density interareal graphs and apparent small-world properties are challenged by data that reveal high-density cortical graphs in which economy of connections is achieved by weight heterogeneity and distance-weight correlations. These properties define a model that predicts many binary and weighted features of the cortical network including a core-periphery, a typical feature of self-organizing information processing systems. Feedback and feedforward pathways between areas exhibit a dual counterstream organization, and their integration into local circuits constrains cortical computation. Here, we propose a bow-tie representation of interareal architecture derived from the hierarchical laminar weights of pathways between the high-efficiency dense core and periphery.</jats:p>

<jats:p>How rich functionality emerges from the invariant structural architecture of the brain remains a major mystery in neuroscience. Recent applications of network theory and theoretical neuroscience to large-scale brain networks have started to dissolve this mystery. Network analyses suggest that hierarchical modular brain networks are particularly suited to facilitate local (segregated) neuronal operations and the global integration of segregated functions. Although functional networks are constrained by structural connections, context-sensitive integration during cognition tasks necessarily entails a divergence between structural and functional networks. This degenerate (many-to-one) function-structure mapping is crucial for understanding the nature of brain networks. The emergence of dynamic functional networks from static structural connections calls for a formal (computational) approach to neuronal information processing that may resolve this dialectic between structure and function.</jats:p>

<jats:title>Dinner Time!</jats:title> <jats:p> Biological clocks allow organisms to anticipate cycles of feeding, activity, and rest so that metabolic enzymes in mitochondria are ready when needed. <jats:bold> Peek <jats:italic>et al.</jats:italic> </jats:bold> ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.1243417">10.1126/science.1243417</jats:related-article> , published online 19 September; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6158" page="570" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1246658"> <jats:bold>Rey and Reddy</jats:bold> </jats:related-article> ) describe a mechanism by which the biochemical elements of the circadian clock are linked to such control of mitochondrial metabolism. The clock controls rhythmic transcription of the gene encoding the rate-limiting enzyme required for synthesis of nicotinamide adenine dinucleotide (NAD <jats:sup>+</jats:sup> ). The concentration of NAD <jats:sup>+</jats:sup> in mitochondria determines the activity of the deacetylase SIRT3, which then controls acetylation and activity of key metabolic enzymes. NAD+ also influences clock function, and thus appears to be a versatile point at which regulation of oxidative metabolism is coordinated with the daily cycles of energy consumption. </jats:p>