• 2D semiconductor nonlinear plasmonic modulators

      Klein, Matthew; Badada, Bekele H; Binder, Rolf; Alfrey, Adam; McKie, Max; Koehler, Michael R; Mandrus, David G; Taniguchi, Takashi; Watanabe, Kenji; LeRoy, Brian J; et al. (NATURE PUBLISHING GROUP, 2019-07-22)
      A plasmonic modulator is a device that controls the amplitude or phase of propagating plasmons. In a pure plasmonic modulator, the presence or absence of a plasmonic pump wave controls the amplitude of a plasmonic probe wave through a channel. This control has to be mediated by an interaction between disparate plasmonic waves, typically requiring the integration of a nonlinear material. In this work, we demonstrate a 2D semiconductor nonlinear plasmonic modulator based on a WSe2 monolayer integrated on top of a lithographically defined metallic waveguide. We utilize the strong interaction between the surface plasmon polaritons (SPPs) and excitons in the WSe2 to give a 73 % change in transmission through the device. We demonstrate control of the propagating SPPs using both optical and SPP pumps, realizing a 2D semiconductor nonlinear plasmonic modulator, with an ultrafast response time of 290 fs.
    • A wind-albedo-wind feedback driven by landscape evolution

      Abell, Jordan T.; Pullen, Alex; Lebo, Zachary J.; Kapp, Paul; Gloege, Lucas; Metcalf, Andrew R.; Nie, Junsheng; Winckler, Gisela; Univ Arizona, Dept Geosci (NATURE PUBLISHING GROUP, 2020-01)
      The accurate characterization of near-surface winds is critical to our understanding of past and modern climate. Dust lofted by these winds has the potential to modify surface and atmospheric conditions as well as ocean biogeochemistry. Stony deserts, low dust emitting regions today, represent expansive areas where variations in surficial geology through time may drastically impact near-surface conditions. Here we use the Weather Research and Forecasting (WRF) model over the western Gobi Desert to demonstrate a previously undocumented process between wind-driven landscape evolution and boundary layer conditions. Our results show that altered surficial thermal properties through winnowing of fine-grained sediments and formation of low-albedo gravel-mantled surfaces leads to an increase in near-surface winds by up to 25%; paradoxically, wind erosion results in faster winds regionally. This wind-albedo-wind feedback also leads to an increase in the frequency of hours spent at higher wind speeds, which has implications for dust emission potential.
    • Accelerated nonlinear interactions in graded-index multimode fibers

      Eftekhar, M A; Sanjabi-Eznaveh, Z; Lopez-Aviles, H E; Benis, S; Antonio-Lopez, J E; Kolesik, M; Wise, F; Amezcua-Correa, R; Christodoulides, D N; Univ Arizona, Coll Opt Sci (NATURE PUBLISHING GROUP, 2019-04-09)
      Multimode optical fibers have recently reemerged as a viable platform for addressing a number of long-standing issues associated with information bandwidth requirements and power-handling capabilities. As shown in recent studies, the complex nature of such heavily multimoded systems can be effectively exploited to observe altogether novel physical effects arising from spatiotemporal and intermodal linear and nonlinear processes. Here, we study for the first time, accelerated nonlinear intermodal interactions in core-diameter decreasing multimode fibers. We demonstrate that in the anomalous dispersion region, this spatiotemporal acceleration can lead to relatively blue-shifted multimode solitons and blue-drifting dispersive wave combs, while in the normal domain, to a notably flat and uniform supercontinuum, extending over 2.5 octaves. Our results pave the way towards a deeper understanding of the physics and complexity of nonlinear, heavily multimoded optical systems, and could lead to highly tunable optical sources with very high spectral densities.
    • The actin cytoskeletal architecture of estrogen receptor positive breast cancer cells suppresses invasion

      Padilla-Rodriguez, Marco; Parker, Sara S.; Adams, Deanna G.; Westerling, Thomas; Puleo, Julieann I.; Watson, Adam W.; Hill, Samantha M.; Noon, Muhammad; Gaudin, Raphael; Aaron, Jesse; et al. (NATURE PUBLISHING GROUP, 2018-07-30)
      Estrogen promotes growth of estrogen receptor-positive (ER+) breast tumors. However, epidemiological studies examining the prognostic characteristics of breast cancer in postmenopausal women receiving hormone replacement therapy reveal a significant decrease in tumor dissemination, suggesting that estrogen has potential protective effects against cancer cell invasion. Here, we show that estrogen suppresses invasion of ER+ breast cancer cells by increasing transcription of the Ena/VASP protein, EVL, which promotes the generation of suppressive cortical actin bundles that inhibit motility dynamics, and is crucial for the ERmediated suppression of invasion in vitro and in vivo. Interestingly, despite its benefits in suppressing tumor growth, anti-estrogenic endocrine therapy decreases EVL expression and increases local invasion in patients. Our results highlight the dichotomous effects of estrogen on tumor progression and suggest that, in contrast to its established role in promoting growth of ER+ tumors, estrogen has a significant role in suppressing invasion through actin cytoskeletal remodeling.
    • Anomalous Hall magnetoresistance in a ferromagnet

      Yang, Yumeng; Luo, Ziyan; Wu, Haijun; Xu, Yanjun; Li, Run-Wei; Pennycook, Stephen J.; Zhang, Shufeng; Wu, Yihong; Univ Arizona, Dept Phys (NATURE PUBLISHING GROUP, 2018-06-08)
      The anomalous Hall effect, observed in conducting ferromagnets with broken time-reversal symmetry, offers the possibility to couple spin and orbital degrees of freedom of electrons in ferromagnets. In addition to charge, the anomalous Hall effect also leads to spin accumulation at the surfaces perpendicular to both the current and magnetization direction. Here, we experimentally demonstrate that the spin accumulation, subsequent spin backflow, and spin-charge conversion can give rise to a different type of spin current-related spin current related magnetoresistance, dubbed here as the anomalous Hall magnetoresistance, which has the same angular dependence as the recently discovered spin Hall magnetoresistance. The anomalous Hall magnetoresistance is observed in four types of samples: co-sputtered (Fe1-xMnx)(0.6)Pt-0.4, Fe1-xMnx/Pt multilayer, Fe1-xMnx with x = 0.17-0.65 and Fe, and analyzed using the drift-diffusion model. Our results provide an alternative route to study charge-spin conversion in ferromagnets and to exploit it for potential spintronic applications.
    • ASPP proteins discriminate between PP1 catalytic subunits through their SH3 domain and the PP1 C-tail

      Bertran, M Teresa; Mouilleron, Stéphane; Zhou, Yanxiang; Bajaj, Rakhi; Uliana, Federico; Kumar, Ganesan Senthil; van Drogen, Audrey; Lee, Rebecca; Banerjee, Jennifer J; Hauri, Simon; et al. (NATURE PUBLISHING GROUP, 2019-02-15)
      Serine/threonine phosphatases such as PP1 lack substrate specificity and associate with a large array of targeting subunits to achieve the requisite selectivity. The tumour suppressor ASPP (apoptosis-stimulating protein of p53) proteins associate with PP1 catalytic subunits and are implicated in multiple functions from transcriptional regulation to cell junction remodelling. Here we show that Drosophila ASPP is part of a multiprotein PP1 complex and that PP1 association is necessary for several in vivo functions of Drosophila ASPP. We solve the crystal structure of the human ASPP2/PP1 complex and show that ASPP2 recruits PP1 using both its canonical RVxF motif, which binds the PP1 catalytic domain, and its SH3 domain, which engages the PP1 C-terminal tail. The ASPP2 SH3 domain can discriminate between PP1 isoforms using an acidic specificity pocket in the n-Src domain, providing an exquisite mechanism where multiple motifs are used combinatorially to tune binding affinity to PP1.
    • Association study in African-admixed populations across the Americas recapitulates asthma risk loci in non-African populations

      Daya, Michelle; Rafaels, Nicholas; Brunetti, Tonya M; Chavan, Sameer; Levin, Albert M; Shetty, Aniket; Gignoux, Christopher R; Boorgula, Meher Preethi; Wojcik, Genevieve; Campbell, Monica; et al. (NATURE PUBLISHING GROUP, 2019-02-20)
      Asthma is a complex disease with striking disparities across racial and ethnic groups. Despite its relatively high burden, representation of individuals of African ancestry in asthma genome-wide association studies (GWAS) has been inadequate, and true associations in these underrepresented minority groups have been inconclusive. We report the results of a genome-wide meta-analysis from the Consortium on Asthma among African Ancestry Populations (CAAPA; 7009 asthma cases, 7645 controls). We find strong evidence for association at four previously reported asthma loci whose discovery was driven largely by non-African populations, including the chromosome 17q12-q21 locus and the chr12q13 region, a novel (and not previously replicated) asthma locus recently identified by the Trans-National Asthma Genetic Consortium (TAGC). An additional seven loci reported by TAGC show marginal evidence for association in CAAPA. We also identify two novel loci (8p23 and 8q24) that may be specific to asthma risk in African ancestry populations.
    • A bed nucleus of stria terminalis microcircuit regulating inflammation-associated modulation of feeding

      Wang, Yong; Kim, JungMin; Schmit, Matthew B; Cho, Tiffany S; Fang, Caohui; Cai, Haijiang; Univ Arizona, Dept Neurosci; Univ Arizona, Grad Interdisciplinary Program Neurosci; Univ Arizona, Bio5 Inst; Univ Arizona, Dept Neurol (NATURE PUBLISHING GROUP, 2019-06-24)
      Loss of appetite or anorexia associated with inflammation impairs quality of life and increases morbidity in many diseases. However, the exact neural mechanism that mediates inflammation-associated anorexia is still poorly understood. Here we identified a population of neurons, marked by the expression of protein kinase C-delta, in the oval region of the bed nucleus of the stria terminalis (BNST), which are activated by various inflammatory signals. Silencing of these neurons attenuates the anorexia caused by these inflammatory signals. Our results demonstrate that these neurons mediate bidirectional control of general feeding behaviors. These neurons inhibit the lateral hypothalamus-projecting neurons in the ventrolateral part of BNST to regulate feeding, receive inputs from the canonical feeding regions of arcuate nucleus and parabrachial nucleus. Our data therefore define a BNST microcircuit that might coordinate canonical feeding centers to regulate food intake, which could offer therapeutic targets for feeding-related diseases such as anorexia and obesity.
    • Bi-allelic variants in RNF170 are associated with hereditary spastic paraplegia

      Wagner, Matias; Osborn, Daniel P S; Gehweiler, Ina; Nagel, Maike; Ulmer, Ulrike; Bakhtiari, Somayeh; Amouri, Rim; Boostani, Reza; Hentati, Faycal; Hockley, Maryam M; et al. (NATURE PUBLISHING GROUP, 2019-10-21)
      Alterations of Ca2+ homeostasis have been implicated in a wide range of neurodegenerative diseases. Ca2+ efflux from the endoplasmic reticulum into the cytoplasm is controlled by binding of inositol 1,4,5-trisphosphate to its receptor. Activated inositol 1,4,5-trisphosphate receptors are then rapidly degraded by the endoplasmic reticulum-associated degradation pathway. Mutations in genes encoding the neuronal isoform of the inositol 1,4,5-trisphosphate receptor (ITPR1) and genes involved in inositol 1,4,5-trisphosphate receptor degradation (ERLIN1, ERLIN2) are known to cause hereditary spastic paraplegia (HSP) and cerebellar ataxia. We provide evidence that mutations in the ubiquitin E3 ligase gene RNF170, which targets inositol 1,4,5-trisphosphate receptors for degradation, are the likely cause of autosomal recessive HSP in four unrelated families and functionally evaluate the consequences of mutations in patient fibroblasts, mutant SH-SY5Y cells and by gene knockdown in zebrafish. Our findings highlight inositol 1,4,5-trisphosphate signaling as a candidate key pathway for hereditary spastic paraplegias and cerebellar ataxias and thus prioritize this pathway for therapeutic interventions.
    • Clade diversification dynamics and the biotic and abiotic controls of speciation and extinction rates

      Aguilée, Robin; Gascuel, Fanny; Lambert, Amaury; Ferriere, Regis; Univ Arizona, Dept Ecol & Evolutionary Biol (NATURE PUBLISHING GROUP, 2018-08-01)
      How ecological interactions, genetic processes, and environmental variability jointly shape the evolution of species diversity remains a challenging problem in biology. We developed an individual-based model of clade diversification to predict macroevolutionary dynamics when resource competition, genetic differentiation, and landscape fluctuations interact. Diversification begins with a phase of geographic adaptive radiation. Extinction rates rise sharply at the onset of the next phase. In this phase of niche self-structuring, speciation and extinction processes, albeit driven by biotic mechanisms (competition and hybridization), have essentially constant rates, determined primarily by the abiotic pace of landscape dynamics. The final phase of diversification begins when intense competition prevents dispersing individuals from establishing new populations. Species' ranges shrink, causing negative diversity-dependence of speciation rates. These results show how ecological and microevolutionary processes shape macroevolutionary dynamics and rates; they caution against the notion of ecological limits to diversity, and suggest new directions for the phylogenetic analysis of diversification.
    • Co-evolution of primitive methane-cycling ecosystems and early Earth's atmosphere and climate

      Sauterey, Boris; Charnay, Benjamin; Affholder, Antonin; Mazevet, Stéphane; Ferrière, Régis; Univ Arizona, ENS PSL Univ, Int Ctr Interdisciplinary Global Environm Studies, CNRS; Univ Arizona, Dept Ecol & Evolutionary Biol (NATURE PUBLISHING GROUP, 2020-06-01)
      The history of the Earth has been marked by major ecological transitions, driven by metabolic innovation, that radically reshaped the composition of the oceans and atmosphere. The nature and magnitude of the earliest transitions, hundreds of million years before photosynthesis evolved, remain poorly understood. Using a novel ecosystem-planetary model, we find that pre-photosynthetic methane-cycling microbial ecosystems are much less productive than previously thought. In spite of their low productivity, the evolution of methanogenic metabolisms strongly modifies the atmospheric composition, leading to a warmer but less resilient climate. As the abiotic carbon cycle responds, further metabolic evolution (anaerobic methanotrophy) may feed back to the atmosphere and destabilize the climate, triggering a transient global glaciation. Although early metabolic evolution may cause strong climatic instability, a low CO:CH4 atmospheric ratio emerges as a robust signature of simple methane-cycling ecosystems on a globally reduced planet such as the late Hadean/early Archean Earth.
    • Collisional formation of top-shaped asteroids and implications for the origins of Ryugu and Bennu

      Michel, P; Ballouz, R-L; Barnouin, O S; Jutzi, M; Walsh, K J; May, B H; Manzoni, C; Richardson, D C; Schwartz, S R; Sugita, S; et al. (NATURE PUBLISHING GROUP, 2020-05-27)
      Asteroid shapes and hydration levels can serve as tracers of their history and origin. For instance, the asteroids (162173) Ryugu and (101955) Bennu have an oblate spheroidal shape with a pronounced equator, but contain different surface hydration levels. Here we show, through numerical simulations of large asteroid disruptions, that oblate spheroids, some of which have a pronounced equator defining a spinning top shape, can form directly through gravitational reaccumulation. We further show that rubble piles formed in a single disruption can have similar porosities but variable degrees of hydration. The direct formation of top shapes from single disruption alone can explain the relatively old crater-retention ages of the equatorial features of Ryugu and Bennu. Two separate parent-body disruptions are not necessarily required to explain their different hydration levels. Asteroid shapes and hydration levels can serve as tracers of their history and origin. Here, the authors show top shape asteroids can form directly through gravitational reaccumulation and rubble piles formed in a single disruption can have similar porosities but variable degrees of hydration.
    • Cryo-EM structure of arabinosyltransferase EmbB from Mycobacterium smegmatis

      Tan, Yong Zi; Rodrigues, José; Keener, James E; Zheng, Ruixiang Blake; Brunton, Richard; Kloss, Brian; Giacometti, Sabrina I; Rosário, Ana L; zhang, Lei; Niederweis, Michael; et al. (NATURE PUBLISHING GROUP, 2020-07-07)
      Arabinosyltransferase B (EmbB) belongs to a family of membrane-bound glycosyl-transferases that build the lipidated polysaccharides of the mycobacterial cell envelope, and are targets of anti-tuberculosis drug ethambutol. We present the 3.3 angstrom resolution single-particle cryo-electron microscopy structure of Mycobacterium smegmatis EmbB, providing insights on substrate binding and reaction mechanism. Mutations that confer ethambutol resistance map mostly around the putative active site, suggesting this to be the location of drug binding.
    • Cycles of external dependency drive evolution of avian carotenoid networks

      Badyaev, Alexander V; Posner, Alexander B; Morrison, Erin S; Higginson, Dawn M; Univ Arizona, Dept Ecol & Evolutionary Biol (NATURE PUBLISHING GROUP, 2019-04-08)
      All organisms depend on input of exogenous compounds that cannot be internally produced. Gain and loss of such dependencies structure ecological communities and drive species' evolution, yet the evolution of mechanisms that accommodate these variable dependencies remain elusive. Here, we show that historical cycles of gains and losses of external dependencies in avian carotenoid-producing networks are linked to their evolutionary diversification. This occurs because internalization of metabolic controls-produced when gains in redundancy of dietary inputs coincide with increased branching of their derived products-enables rapid and sustainable exploration of an existing network by shielding it from environmental fluctuations in inputs. Correspondingly, loss of internal controls constrains evolution to the rate of the gains and losses of dietary precursors. Because internalization of a network's controls necessarily bridges diet-specific enzymatic modules within a network, it structurally links local adaptation and continuous evolution even for traits fully dependent on contingent external inputs.
    • Deep phenotyping of 34,128 adult patients hospitalised with COVID-19 in an international network study

      Burn, Edward; You, Seng Chan; Sena, Anthony G; Kostka, Kristin; Abedtash, Hamed; Abrahão, Maria Tereza F; Alberga, Amanda; Alghoul, Heba; Alser, Osaid; Alshammari, Thamir M; et al. (NATURE RESEARCH, 2020-10-06)
      Comorbid conditions appear to be common among individuals hospitalised with coronavirus disease 2019 (COVID-19) but estimates of prevalence vary and little is known about the prior medication use of patients. Here, we describe the characteristics of adults hospitalised with COVID-19 and compare them with influenza patients. We include 34,128 (US: 8362, South Korea: 7341, Spain: 18,425) COVID-19 patients, summarising between 4811 and 11,643 unique aggregate characteristics. COVID-19 patients have been majority male in the US and Spain, but predominantly female in South Korea. Age profiles vary across data sources. Compared to 84,585 individuals hospitalised with influenza in 2014-19, COVID-19 patients have more typically been male, younger, and with fewer comorbidities and lower medication use. While protecting groups vulnerable to influenza is likely a useful starting point in the response to COVID-19, strategies will likely need to be broadened to reflect the particular characteristics of individuals being hospitalised with COVID-19. Detailed knowledge of the characteristics of COVID-19 patients helps with public health planning. Here, the authors use routinely-collected data from seven databases in three countries to describe the characteristics of >30,000 patients admitted with COVID-19 and compare them with those admitted for influenza in previous years.
    • Delocalization of exciton and electron wavefunction in non-fullerene acceptor molecules enables efficient organic solar cells

      Zhang, Guichuan; Chen, Xian-Kai; Xiao, Jingyang; Chow, Philip C. Y.; Ren, Minrun; Kupgan, Grit; Jiao, Xuechen; Chan, Christopher C. S.; Du, Xiaoyan; Xia, Ruoxi; et al. (NATURE PUBLISHING GROUP, 2020-08)
      A major challenge for organic solar cell (OSC) research is how to minimize the tradeoff between voltage loss and charge generation. In early 2019, we reported a non-fullerene acceptor (named Y6) that can simultaneously achieve high external quantum efficiency and low voltage loss for OSC. Here, we use a combination of experimental and theoretical modeling to reveal the structure-property-performance relationships of this state-of-the-art OSC system. We find that the distinctive -pi molecular packing of Y6 not only exists in molecular single crystals but also in thin films. Importantly, such molecular packing leads to (i) the formation of delocalized and emissive excitons that enable small non-radiative voltage loss, and (ii) delocalization of electron wavefunctions at donor/acceptor interfaces that significantly reduces the Coulomb attraction between interfacial electron-hole pairs. These properties are critical in enabling highly efficient charge generation in OSC systems with negligible donor-acceptor energy offset. p id=Par Y6, as a non-fullerene acceptor for organic solar cells, has attracted intensive attention because of the low voltage loss and high charge generation efficiency. Here, Zhang et al. find that the delocalization of exciton and electron wavefunction due to strong pi-pi packing of Y6 is the key for the high performance.
    • Detection of anti-correlation of hot and cold baryons in galaxy clusters

      Farahi, Arya; Mulroy, Sarah L; Evrard, August E; Smith, Graham P; Finoguenov, Alexis; Bourdin, Hervé; Carlstrom, John E; Haines, Chris P; Marrone, Daniel P; Martino, Rossella; et al. (NATURE PUBLISHING GROUP, 2019-07-02)
      The largest clusters of galaxies in the Universe contain vast amounts of dark matter, plus baryonic matter in two principal phases, a majority hot gas component and a minority cold stellar phase comprising stars, compact objects, and low-temperature gas. Hydrodynamic simulations indicate that the highest-mass systems retain the cosmic fraction of baryons, a natural consequence of which is anti-correlation between the masses of hot gas and stars within dark matter halos of fixed total mass. We report observational detection of this anti-correlation based on 4 elements of a 9 x 9-element covariance matrix for nine cluster properties, measured from multi-wavelength observations of 41 clusters from the Local Cluster Substructure Survey. These clusters were selected using explicit and quantitative selection rules that were then encoded in our hierarchical Bayesian model. Our detection of anti-correlation is consistent with predictions from contemporary hydrodynamic cosmological simulations that were not tuned to reproduce this signal.
    • A divisive model of evidence accumulation explains uneven weighting of evidence over time

      Keung, Waitsang; Hagen, Todd A; Wilson, Robert C; Univ Arizona, Cognit Sci Program (NATURE PUBLISHING GROUP, 2020-05-01)
      Divisive normalization has long been used to account for computations in various neural processes and behaviours. The model proposes that inputs into a neural system are divisively normalized by the system's total activity. More recently, dynamical versions of divisive normalization have been shown to account for how neural activity evolves over time in value-based decision making. Despite its ubiquity, divisive normalization has not been studied in decisions that require evidence to be integrated over time. Such decisions are important when the information is not all available at once. A key feature of such decisions is how evidence is weighted over time, known as the integration kernel. Here, we provide a formal expression for the integration kernel in divisive normalization, and show that divisive normalization quantitatively accounts for 133 human participants' perceptual decision making behaviour, performing as well as the state-of-the-art Drift Diffusion Model, the predominant model for perceptual evidence accumulation. Divisive normalization is thought to be a ubiquitous computation in the brain, but has not been studied in decisions that require integrating evidence over time. Here, the authors show in humans that dynamic divisive normalization accounts for the uneven weighting of perceptual evidence over time.
    • Dual-comb spectroscopy of laser-induced plasmas

      Bergevin, Jenna; Wu, Tsung-Han; Yeak, Jeremy; Brumfield, Brian E.; Harilal, Sivanandan S.; Phillips, Mark C.; Jones, R. Jason; Univ Arizona, Coll Opt Sci (NATURE PUBLISHING GROUP, 2018-03-28)
      Dual-comb spectroscopy has become a powerful spectroscopic technique in applications that rely on its broad spectral coverage combined with high frequency resolution capabilities. Experiments to date have primarily focused on detection and analysis of multiple gas species under semi-static conditions, with applications ranging from environmental monitoring of greenhouse gases to high-resolution molecular spectroscopy. Here, we utilize dual-comb spectroscopy to demonstrate broadband, high-resolution, and time-resolved measurements in a laser-induced plasma. As a demonstration, we simultaneously detect trace amounts of Rb and K in solid samples with a single laser ablation shot, with transitions separated by over 6 THz (13 nm) and spectral resolution sufficient to resolve isotopic and ground state hyperfine splittings of the Rb D-2 line. This new spectroscopic approach offers the broad spectral coverage found in the powerful techniques of laser-induced breakdown spectroscopy (LIBS) while providing the high-resolution and accuracy of cw laser-based spectroscopies.
    • The Eighty Five Percent Rule for optimal learning

      Wilson, Robert C; Shenhav, Amitai; Straccia, Mark; Cohen, Jonathan D; Univ Arizona, Dept Psychol; Univ Arizona, Cognit Sci Program (NATURE PUBLISHING GROUP, 2019-11-05)
      Researchers and educators have long wrestled with the question of how best to teach their clients be they humans, non-human animals or machines. Here, we examine the role of a single variable, the difficulty of training, on the rate of learning. In many situations we find that there is a sweet spot in which training is neither too easy nor too hard, and where learning progresses most quickly. We derive conditions for this sweet spot for a broad class of learning algorithms in the context of binary classification tasks. For all of these stochastic gradient-descent based learning algorithms, we find that the optimal error rate for training is around 15.87% or, conversely, that the optimal training accuracy is about 85%. We demonstrate the efficacy of this ‘Eighty Five Percent Rule’ for artificial neural networks used in AI and biologically plausible neural networks thought to describe animal learning.