Neural codes formed by small and temporally precise populations in auditory cortex

The encoding of sensory information by populations of cortical neurons forms the basis for perception but remains poorly understood. To understand the constraints of cortical population coding we analyzed neural responses to natural sounds recorded in auditory cortex of primates (Macaca mulatta). We estimated stimulus information while varying the composition and size of the considered population. Consistent with previous reports we found that when choosing subpopulations randomly from the recorded ensemble, the average population information increases steadily with population size. This scaling was explained by a model assuming that each neuron carried equal amounts of information, and that any overlap between the information carried by each neuron arises purely from random sampling within the stimulus space. However, when studying subpopulations selected to optimize information for each given population size, the scaling of information was strikingly different: a small fraction of temporally precise cells carried the vast majority of information. This scaling could be explained by an extended model, assuming that the amount of information carried by individual neurons was highly nonuniform, with few neurons carrying large amounts of information. Importantly, these optimal populations can be determined by a single biophysical marker—the neuron's encoding time scale—allowing their detection and readout within biologically realistic circuits. These results show that extrapolations of population information based on random ensembles may overestimate the population size required for stimulus encoding, and that sensory cortical circuits may process information using small but highly informative ensembles

Population-based neuropathological studies of dementia: design, methods and areas of investigation – a systematic review

Background Prospective population-based neuropathological studies have a special place in dementia research which is under emphasised. Methods A systematic review of the methods of population-based neuropathological studies of dementia was carried out. These studies were assessed in relation to their representativeness of underlying populations and the clinical, neuropsychological and neuropathological approaches adopted. Results Six studies were found to be true population-based neuropathological studies of dementia in the older people: the Hisayama study (Japan); Vantaa 85+ study (Finland); CC75C study (Cambridge, UK); CFAS (multicentre, UK); Cache County study (Utah, USA); HAAS (Hawaï, USA). These differ in the core characteristics of their populations. The studies used standardised neuropathological methods which facilitate analyses on: clinicopathological associations and confirmation of diagnosis, assessing the validity of hierarchical models of neuropathological lesion burden; investigating the associations between neuropathological burden and risk factors including genetic factors. Examples of findings are given although there is too little overlap in the areas investigated amongst these studies to form the basis of a systematic review of the results. Conclusion Clinicopathological studies based on true population samples can provide unique insights in dementia. Individually they are limited in power and scope; together they represent a powerful source to translate findings from laboratory to populations

To beta block or not to beta block; that is the question

The fast-acting β-1 blocker esmolol has been the center of attention since the landmark article by Morrelli and colleagues suggesting that, in patients with sepsis, reducing heart rate by administering esmolol can result in a survival benefit. However, the use of esmolol for the treatment of sepsis and the underlying mechanism responsible for this benefit remain controversial. This commentary discusses the study by Jacquet-Lagrèze and colleagues, who in a pig model of sepsis tested the hypothesis that administration of esmolol to reduce heart rate may correct sepsis-induced sublingual and gut microcirculatory alterations which are known to be associated with adverse outcome

Investigating the governing factors influencing the pozzolanic activity through a database approach for the development of sustainable cementitious materials

Pozzolans, known to possess high pozzolanic activity, enhances the long-term engineering properties of concrete due to the consumption of calcium hydroxide and the consequent formation of the calcium-silicate-hydrate gels within the cementitious matrix. Although the key factors that affect the pozzolanic activity such as the chemical composition, amorphousness, and fineness are commonly addressed in literature, there is a growing need to further gain an insight into the factors that govern this activity in a more comprehensive approach. The aim of this empirical study is to develop concrete models comprising optimal replacement of pozzolans based on the governing factors affecting the activity through the database approach. The database, consisting of 631 number of data points harvested from the literature, is established to determine the optimum replacement levels of the designated pozzolans in concrete. The governing factors therefore played a key role in establishing the boundary conditions that enabled the potential concrete models to be generated particularly for the sustainability assessment of concrete incorporating pozzolans. The study shows that the optimum replacement levels in con- crete mixtures are 15–50% for GGBS, 10–35% for fly ash, and 5–15% for silica fume. The study furthermore demonstrated that the utilisation of these substitutions leaded a considerable reduction in carbon emissions that ranged from 13% to 43% for GGBS, 9–31% for fly ash, and 4–13% for silica fume. The study significantly contributes to the generation of greener construction materials, and offers a cleaner disposal route for the pozzolans principally compared to the traditional waste management alternatives

Monitoring coherence between the macro and microcirculation in septic shock

Purpose of review Currently, the treatment of patients with shock is focused on the clinical symptoms of shock. In the early phase, this is usually limited to heart rate, blood pressure, lactate levels and urine output. However, as the ultimate goal of resuscitation is the improvement in microcirculatory perfusion the question is whether these currently used signs of shock and the improvement in these signs actually correspond to the changes in the microcirculation. Recent findings Recent studies have shown that during the development of shock the deterioration in the macrocirculatory parameters are followed by the deterioration of microcirculatory perfusion. However, in many cases the restoration of adequate macrocirculatory parameters is frequently not associated with improvement in microcirculatory perfusion. This relates not only to the cause of shock, where there are some differences between different forms of shock, but also to the type of treatment. Summary The improvement in macrohemodynamics during the resuscitation is not consistently followed by subsequent changes in the microcirculation. This may result in both over-resuscitation and under-resuscitation le

A wave driver theory for vortical waves propagating across junctions with application to those between rigid and compliant walls

A theory is described for propagation of vortical waves across alternate rigid and compliant panels. The structure in the fluid side at the junction of panels is a highly vortical narrow viscous structure which is idealized as a wave driver. The wave driver is modelled as a ‘half source cum half sink’. The incoming wave terminates into this structure and the outgoing wave emanates from it. The model is described by half Fourier–Laplace transforms respectively for the upstream and downstream sides of the junction. The cases below cutoff and above cutoff frequencies are studied. The theory completely reproduces the direct numerical simulation results of Davies & Carpenter (J. Fluid Mech., vol. 335, 1997, p. 361). Particularly, the jumps across the junction in the kinetic energy integral, the vorticity integral and other related quantities as obtained in the work of Davies & Carpenter are completely reproduced. Also, some important new concepts emerge, notable amongst which is the concept of the pseudo group velocity

Concept for a resource-efficient process chain for hybrid bulk components with optimized energy utilization

A significant percentage of energy in hot forming is used to heat the components. Especially in manufacturing hybrid components, workpieces are heated in the preceding hot-joining process in addition to the heating cycles. Nevertheless, previous processing steps require longer times than the following hot forming processes leading to long downtimes. With the pre-production of workpieces, the machine's capacity is fully utilized but prevents the reuse of the residual heat. Consequently, an immense amount of energy is wasted due to additionally required heating cycles. Our approach is to develop a flexible and resource-efficient process chain. We combine two hot forming processes with different cycle times in a single process chain. Therefore, we consider the process of a hybrid bevel gear with heat and time-consuming preparation and a hybrid shaft with moderate preparation effort. To compensate for the bevel gear's high cycle times, the shaft is hot-formed during the downtimes. In order to reuse the residual heat of the bevel gear, their hot-forming process run is prioritized: Whenever the bevel gear's workpiece is manufactured, it will be hot-formed immediately. Combining these process chains allows the forming machine's capacity to be fully utilized and energy utilization optimized

Mean-field analysis of the majority-vote model broken-ergodicity steady state

We study analytically a variant of the one-dimensional majority-vote model in which the individual retains its opinion in case there is a tie among the neighbors' opinions. The individuals are fixed in the sites of a ring of size $L$ and can interact with their nearest neighbors only. The interesting feature of this model is that it exhibits an infinity of spatially heterogeneous absorbing configurations for $L \to \infty$ whose statistical properties we probe analytically using a mean-field framework based on the decomposition of the $L$-site joint probability distribution into the $n$-contiguous-site joint distributions, the so-called $n$-site approximation. To describe the broken-ergodicity steady state of the model we solve analytically the mean-field dynamic equations for arbitrary time $t$ in the cases n=3 and 4. The asymptotic limit $t \to \infty$ reveals the mapping between the statistical properties of the random initial configurations and those of the final absorbing configurations. For the pair approximation ($n=2$) we derive that mapping using a trick that avoids solving the full dynamics. Most remarkably, we find that the predictions of the 4-site approximation reduce to those of the 3-site in the case of expectations involving three contiguous sites. In addition, those expectations fit the Monte Carlo data perfectly and so we conjecture that they are in fact the exact expectations for the one-dimensional majority-vote model

Regional ischemia in hypertrophic Langendorff-perfused rat hearts

Myocardial hypertrophy decreases the muscle mass-to-vascularization ratio, thereby changing myocardial perfusion. The effect of these changes on myocardial oxygenation in hypertrophic Langendorff-perfused rat hearts was measured using epimyocardial NADH videofluorimetry, whereby ischemic myocardium displays a high fluorescence intensity. Hypertrophic hearts, in contrast to control hearts, developed ischemic areas during oxygen-saturated Langendorff perfusion. Reoxygenation of control hearts after a hypoxic episode resulted in a swift decrease of fluorescence in a heterogeneous pattern of small, evenly dispersed, highly fluorescent patches. Identical patterns could be evoked by occluding capillaries with microspheres 5.9 micrometer in diameter. Ten seconds after reoxygenation there were no more dysoxic areas, whereas reoxygenation in hypertrophic hearts showed larger ischemic areas that took significantly longer to return to normoxic fluorescence intensities. Hypothesizing that the larger areas originate at a vascular level proximal to the capillary network, we induced hypoxic patterns by embolizing control hearts with microspheres 9.8 and 15 micrometer in diameter. The frequency distribution histograms of these dysoxic surface areas matched those of hypertrophic hearts and differed significantly from those of hearts embolized with 5.9-micrometer microspheres. These results suggest the existence of areas in hypertrophic Langendorff-perfused hearts with suboptimal vascularization originating at the arteriolar and/or arterial level