Hearing it again and again: on-line subcortical plasticity in humans

Background

Human brainstem activity is sensitive to local sound statistics, as reflected in an enhanced response in repetitive compared to pseudo-random stimulus conditions [1]. Here we probed the short-term time course of this enhancement using a paradigm that assessed how the local sound statistics (i.e., repetition within a five-note melody) interact with more global statistics (i.e., repetition of the melody).

Methodology/Principal Findings

To test the hypothesis that subcortical repetition enhancement builds over time, we recorded auditory brainstem responses in young adults to a five-note melody containing a repeated note, and monitored how the response changed over the course of 1.5 hrs. By comparing response amplitudes over time, we found a robust time-dependent enhancement to the locally repeating note that was superimposed on a weaker enhancement of the globally repeating pattern.

Conclusions/Significance

We provide the first demonstration of on-line subcortical plasticity in humans. This complements previous findings that experience-dependent subcortical plasticity can occur on a number of time scales, including life-long experiences with music and language, and short-term auditory training. Our results suggest that the incoming stimulus stream is constantly being monitored, even when the stimulus is physically invariant and attention is directed elsewhere, to augment the neural response to the most statistically salient features of the ongoing stimulus stream. These real-time transformations, which may subserve humans'' strong disposition for grouping auditory objects, likely reflect a mix of local processes and corticofugal modulation arising from statistical regularities and the influences of expectation. Our results contribute to our understanding of the biological basis of statistical learning and initiate a new investigational approach relating to the time-course of subcortical plasticity. Although the reported time-dependent enhancements are believed to reflect universal neurophysiological processes, future experiments utilizing a larger array of stimuli are needed to establish the generalizability of our findings.     

Once again on the components of pairwise beta diversity

Presence–absence based beta diversity defined for pairs of sites may be partitioned into components following two different ways of thinking. Within the framework of Baselga (abbreviated hereafter as BAS), nestedness is crucial and dissimilarity is partitioned into replacement (turnover) and nestedness-resultant fractions. The method proposed by Podani and Schmera (POD), however, places emphasis on the mathematical additivity of components and divides dissimilarity into replacement and richness difference components. A recent comparison by Baselga and Leprieur (2015), on the example of the Jaccard family of indices, emphasizes the independence of replacement component from absolute richness difference and concludes that the replacement function of the BAS framework is the only true measure of species replacement. As a response to this study, we show here that 1) the sacrifice one must make for independence is that the components themselves are scaled differently and are not always comparable ecologically, 2) absolute (raw) replacement and richness difference are not independent, so that independence from the latter cannot be a fundamental criterion that a replacement measure should satisfy, 3) relativization applied in the POD framework is ecologically interpretable, leading to a meaningful conceptualization of species replacement, 4) the BAS and POD methods are linked through a generalized replacement function, 5) both the BAS and POD approaches may produce high correlations with environmental variables, whereas 6) the POD approach offers in many respects more illuminating demonstrations of the underlying changes of pattern than the graphs of Baselga and Leprieur for both artificial and actual fish distribution data.     

Oh no, Notch again!

The Notch receptor signaling pathway is important for morphogenesis and development of many organs and tissues in most if not all multicellular species. The classical view holds that Notch signaling keeps cells in an undifferentiated state. Recently, however, this notion has been challenged in the nervous system by two sets of observations: Notch plays an active role in the differentiation of glial cells,(1-4) and Notch influences the length and organisation of neuronal processes.(5-7) In this review, we analyse these recent data and discuss how Notch signaling may be able to perform such quite different tasks during nervous system development. BioEssays 23:3-7, 2001.     

Gaia again

The ideas of the Gaia hypothesis from the 1960s are today largely included in global ecology and Earth system sciences. The interdependence between biosphere, oceans, atmosphere and geosphere is well-established by data from global monitoring. Nevertheless the theory underlying the holistic view of the homeostatic Earth has remained obscure. Here the foundations of Gaia theory are examined from the recent formulation of the 2nd law of thermodynamics as an equation of motion. According to the principle of increasing entropy, all natural processes, inanimate just as animate, consume free energy, the thermodynamic driving force. All species, abiotic just as biotic are viewed as mechanisms of energy transduction for the global system to evolve toward a stationary state in its surroundings. The maximum entropy state displays homeostasis by being stable against internal fluctuations. When surrounding conditions change or when new mechanisms emerge, the global system readjusts its flows of energy to level newly appeared gradients. Thus, the propositions of Gaia theory and holistic understanding of the global system are recognized as consequences of thermodynamic imperatives.     

Diego and friends play again

The formation of properly differentiated organs often requires the planar coordination of cell polarization within the tissues. Such planar cell polarization (PCP) events are best studied in Drosophila, where many of the key players, known as PCP genes, have already been identified. Genetic analysis of the PCP genes suggests that the establishment of polarity consists of three major steps. The first step involves the generation of a global polarity cue; this in turn promotes the second step, the redistribution of the core PCP proteins, leading to the formation of asymmetrically localized signaling centers. During the third step, these complexes control tissue-specific cellular responses through the activation of cell type specific effector genes. Here we discuss some of the most recent advances that have provided valuable new insight into each of the three major steps of planar cell polarization.     

Stem cells make leukemia grow again

Leukemic stem cells were hypothesized to play a critical role in acute myeloid leukemia relapse, but data to support this were lacking. In a recent study elegantly combining sequencing with functional xenograft assays, Shlush et al ( 2017 ) identified two distinct origins of leukemic relapse. They provided direct experimental evidence linking relapse to cancer stem cell clones already present before therapeutic intervention.     

Cutaneous cancer stem cells: beta-catenin strikes again

Cancer stem cells (CSCs) are a subpopulation of tumor cells that retain properties of tissue-specific stem cells, including the ability to self-renew. In a recent article in Nature, Malanchi et al. (2008) identified a population of CD34(+) cells in epidermal tumors that require beta-catenin signaling to maintain a CSC phenotype.     

Out of Amazonia again and again: episodic crossing of the Andes promotes diversification in a lowland forest flycatcher

Most Neotropical lowland forest taxa occur exclusively on one side of the Andes despite the availability of appropriate habitat on both sides. Almost all molecular phylogenies and phylogenetic analyses of species assemblages (i.e. area cladograms) have supported the hypothesis that Andean uplift during the Late Pliocene created a vicariant barrier affecting lowland lineages in the region. However, a few widespread plant and animal species occurring in lowland forests on both sides of the Andes challenge the generality of this hypothesis. To understand the role of the Andes in the history of such organisms, we reconstructed the phylogeographic history of a widespread Neotropical flycatcher (Mionectes oleagineus) in the context of the other four species in the genus. A molecular phylogeny based on nuclear and mitochondrial sequences unambiguously showed an early basal split between montane and lowland Mionectes. The phylogeographic reconstruction of lowland taxa revealed a complex history, with multiple cases in which geographically proximate populations do not represent sister lineages. Specifically, three populations of M. oleagineus west of the Andes do not comprise a monophyletic clade; instead, each represents an independent lineage with origins east of the Andes. Divergence time estimates suggest that at least two cross-Andean dispersal events post-date Andean uplift.     

Rethinking heredity, again

The refutation of 'soft' inheritance and establishment of Mendelian genetics as the exclusive model of heredity is widely portrayed as an iconic success story of scientific progress. Yet, we are witnessing a re-emergence of debate on the role of soft inheritance in heredity and evolution. I argue that this reversal reflects not only the weight of new evidence but also an important conceptual change. I show that the concept of soft inheritance rejected by 20th-century genetics differs fundamentally from the current concept of 'nongenetic inheritance'. Moreover, whereas it has long been assumed that heredity is mediated by a single, universal mechanism, a pluralistic model of heredity is now emerging, based on a recognition of multiple, parallel mechanisms of inheritance.     

ER strikes again: Proteostasis Dysfunction In ALS

The precise contribution of endoplasmic reticulum (ER) chaperone protein disulfide isomerase (PDI) variants in human amyotrophic lateral sclerosis (ALS) patients to the pathogenesis of ALS remained unclear. In the present study, Woehlbier et al ( 2016 ) demonstrated that these PDI variants are capable of altering motor neuron morphology, impairing the expression of synaptic proteins, and compromising neuromuscular junction (NMJ) integrity.     

Calcium signalling: IP3 rises again...and again

Recent results indicate that 'regulators of G-protein signalling' may contribute to the generation of receptor-specific patterns of cytosolic Ca2+ oscillations by associating with specific receptors, accelerating G-protein inactivation and responding to changes in cytosolic Ca2+.     

DUSPs strike again

Comment on: Kozarova A, et al. Cell Cycle 2011; 10:1669-78.     

Understanding circadian rhythmicity in Neurospora crassa: from behavior to genes and back again

Circadian clocks have been described in organisms ranging in complexity from unicells to mammals, in which they function to control daily rhythms in cellular activities and behavior. The significance of a detailed understanding of the clock can be appreciated by its ubiquity and its established involvement in human physiology, including endocrine function, sleep/wake cycles, psychiatric illness, and drug tolerances and effectiveness. Because the clock in all organisms is assembled within the cell and clock mechanisms are evolutionarily conserved, simple eukaryotes provide appropriate experimental systems for dissecting the clock. Significant progress has been made in deciphering the circadian system in Neurospora crassa using both genetic and molecular approaches, and Neurospora has contributed greatly to our understanding of (1) the feedback cycle that comprises a circadian oscillator, (2) the mechanisms by which the clock is kept in synchrony with the environment, and (3) the genes that reside in rhythmic output pathways. Importantly, the lessons learned in Neurospora are relevant to our understanding of clocks in higher eukaryotes.     

From stem cell to progenitor and back again

Under normal homeostatic conditions, tissue stem cells undergo long-term self renewal and produce progeny that differentiate into several different cell types. But what happens if the stem cells are lost? In a recent issue of Developmental Cell, Nakagawa et al. (2007) propose that the progeny of stem cells, called transit-amplifying progenitor cells, are able to replace lost stem cells.     

Putting cells together again.

Computational biologists are trying to combine the pieces of knowledge about the cell to develop a bigger picture. Such a 'virtual cell' is proving useful for the simulation of cellular processes, reports Michael Gross.     

Replication licensing: oops! ... I did it again

All eukaryotes use multiple controls to restrict DNA replication to once per cell cycle. Nevertheless, inactivation of a single gene, cul-4, causes massive re-replication in Caenorhabditis elegans. A novel study explains this dramatic phenotype by demonstrating that the CUL-4 E3 ligase simultaneously controls two critical licensing factors: CDT-1 and CDC-6.     

Synaptic vesicles caught kissing again

In this issue of Neuron, Harata et al. use a novel quenching technique to provide compelling evidence that kiss-and-run is the dominant mode of vesicle fusion at hippocampal synapses and that the prevalence of kiss-and-run can be modulated by stimulus frequency. The increased incidence of kiss-and-run at lower frequencies may ensure that vesicles are available for use during periods of high demand.