In prey species such as mice, avoidance of predators is key to survival and drives instinctual behaviors like freeze or flight 1, 2. Sensory signals guide the selection of appropriate behavior 3, and ...for aerial predators only vision provides useful information. Surprisingly, there is no evidence that vision can guide the selection of escape strategies. Fleeing behavior can be readily triggered by a rapidly looming overhead stimulus 4. Freezing behavior, however, has previously been induced by real predators or their odors 5. Here, we discover that a small moving disk, simulating the sweep of a predator cruising overhead, is sufficient to induce freezing response in mice. Looming and sweeping therefore provide visual triggers for opposing flight and freeze behaviors and provide evidence that mice innately make behavioral choices based on vision alone.
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•Rodents use vision to choose how to respond to an overhead threat•A moving disk induces freezing, while an expanding disk induces flight responses•Opposing innate behaviors can be induced by visual stimuli
De Franceschi et al. discover that the visual simulation of a predator cruising overhead induces freezing responses in mice. Visual simulation of a rapidly approaching predator instead induces flight responses. These findings provide evidence that mice innately make behavioral choices based on vision alone.
How an object is perceived depends on the temporal context in which it is encountered. Sensory signals in the brain also depend on temporal context, a phenomenon often referred to as adaptation. ...Traditional descriptions of adaptation effects emphasize various forms of response fatigue in single neurons, which grow in strength with exposure to a stimulus. Recent work on vision, and other sensory modalities, has shown that this description has substantial shortcomings. Here we review our emerging understanding of how adaptation alters the balance between excitatory and suppressive signals, how effects depend on adaptation duration, and how adaptation influences representations that are distributed within and across multiple brain structures. This work points to a sophisticated set of mechanisms for adjusting to recent sensory experience, and suggests new avenues for understanding their function.
Solomon and Kohn review our emerging understanding of how adaptation alters the balance between excitatory and suppressive sensory signals, how effects depend on adaptation duration, and how adaptation influences representations distributed within and across multiple brain structures.
The focus of the present work is to perform parametric studies on the performance of a packed bed storage unit filled with phase change material (PCM) encapsulated spherical containers, suitable for ...low temperature solar air heating applications. A parametric analysis was carried out using the validated enthalpy based numerical model that considers the thermal gradient inside the PCM container. The results of simulation analysis showed that the size of the PCM ball, fluid inlet temperature and the mass flow rate of the heat transfer fluid (HTF) influenced respectively the heat transfer area in the packed bed, temperature difference between the HTF and PCM and the surface convective heat transfer coefficient between the HTF and PCM balls. The poor thermal conductivity of the PCM has only negligible effect on heat transfer due to high surface convective resistance provided by the air. The influence of various parameters for the selected range of values were analyzed using the charging time, instantaneous heat stored and cumulative heat stored during the charging process.
Near-infrared spectroscopy (NIRS) is a noninvasive neuroimaging tool for studying evoked hemodynamic changes within the brain. By this technique, changes in the optical absorption of light are ...recorded over time and are used to estimate the functionally evoked changes in cerebral oxyhemoglobin and deoxyhemoglobin concentrations that result from local cerebral vascular and oxygen metabolic effects during brain activity. Over the past three decades this technology has continued to grow, and today NIRS studies have found many niche applications in the fields of psychology, physiology, and cerebral pathology. The growing popularity of this technique is in part associated with a lower cost and increased portability of NIRS equipment when compared with other imaging modalities, such as functional magnetic resonance imaging and positron emission tomography. With this increasing number of applications, new techniques for the processing, analysis, and interpretation of NIRS data are continually being developed. We review some of the time-series and functional analysis techniques that are currently used in NIRS studies, we describe the practical implementation of various signal processing techniques for removing physiological, instrumental, and motion-artifact noise from optical data, and we discuss the unique aspects of NIRS analysis in comparison with other brain imaging modalities. These methods are described within the context of the MATLAB-based graphical user interface program, HomER, which we have developed and distributed to facilitate the processing of optical functional brain data.
Atmospheric nitrogen dioxide (NO.sub.2) pollution is a major health and social challenge in South African induced mainly by fossil fuel combustions for power generation, transportation and domestic ...biomass burning for indoor activities. The pollution level is moderated by various environmental and social factors, yet previous studies made use of limited factors or focussed on only industrialised regions ignoring the contributions in large parts of the country. There is a need to assess how socio-environmenral factors, which inherently exhibit variations across space, influence the pollution levels in South Africa. This study therefore aimed to predict annual tropospheric NO.sub.2 column density using socio-environmental variables that are widely proven in the literature as sources and sinks of pollution. The environmental variables used to predict NO.sub.2 included remotely sensed Enhanced Vegetation Index (EVI), Land Surface Temperature and Aerosol Optical Depth (AOD) while the social data, which were obtained from national household surveys, included energy sources data, settlement patterns, gender and age statistics aggregated at municipality scale. The prediction was accomplished by applying the Multiscale Geographically Weighted Regression that fine-tunes the spatial scale of each variable when building geographically localised relationships. The model returned an overall R.sup.2 of 0.92, indicating good predicting performance and the significance of the socio-environmental variables in estimating NO.sub.2 in South Africa. From the environmental variables, AOD had the most influence in increasing NO.sub.2 pollution while vegetation represented by EVI had the opposite effect of reducing the pollution level. Among the social variables, household electricity and wood usage had the most significant contributions to pollution. Communal residential arrangements significantly reduced NO.sub.2, while informal settlements showed the opposite effect. The female proportion was the most important demographic variable in reducing NO.sub.2 . Age groups had mixed effects on NO.sub.2 pollution, with the mid-age group (20-29) being the most important contributor to NO.sub.2 emission. The findings of the current study provide evidence that NO.sub.2 pollution is explained by socio-economic variables that vary widely across space. This can be achieved reliably using the MGWR approach that produces strong models suited to each locality.
Despite savannas being known for their relatively sparse vegetation coverage compared to other vegetation ecosystems, they harbour functionally diverse vegetation forms. Savannas are affected by ...climate variability and anthropogenic factors, resulting in changes in woody plant species compositions. Monitoring woody plant species diversity is therefore important to inform sustainable biodiversity management. Remote sensing techniques are used as an alternative approach to labour-intensive field-based inventories, to assess savanna biodiversity. The aim of this paper is to review studies that applied remote sensing to assess woody plant species diversity in savanna environments. The paper first provides a brief account of the spatial distribution of savanna environments around the globe. Thereafter, it briefly defines categorical classification and continuous-scale species diversity assessment approaches for savanna woody plant estimation. The core review section divides previous remote sensing studies into categorical classification and continuous-scale assessment approaches. Within each division, optical, Radio Detection And Ranging (RADAR) and Light Detection and Ranging (LiDAR) remote sensing as applied to savanna woody species diversity is reviewed. This is followed by a discussion on multi-sensor applications to estimate woody plant species diversity in savanna. We recommend that future research efforts should focus strongly on routine application of optical, RADAR and LiDAR remote sensing of physiologically similar woody plant species in savannas, as well as on extending these methodological approaches to other vegetation environments.
Key points
In rodents, including mice, the superior colliculus is the major target of the retina, but its visual response is not well characterized.
In the present study, extracellular recordings ...from single nerve cells in the superficial layers of the superior colliculus were made in awake, head‐restrained mice, and their responses to visual stimuli were measured.
It was found that these neurons show brisk, highly sensitive and short latency visual responses, a preference for black over white stimuli, and diverse responses to moving patterns.
At least five broad classes can be defined by variation in functional properties among units.
The results of the present study demonstrate that eye movements have a measurable impact on visual responses in awake animals and show how they may be mitigated in analyses.
The mouse is an increasingly important animal model of visual function in health and disease. In mice, most retinal signals are routed through the superficial layers of the midbrain superior colliculus, and it is well established that much of the visual behaviour of mice relies on activity in the superior colliculus. The functional organization of visual signals in the mouse superior colliculus is, however, not well established in awake animals. We therefore made extracellular recordings from the superficial layers of the superior colliculus in awake mice, while the animals were viewing visual stimuli including flashed spots and drifting gratings. We find that neurons in the superficial layers of the superior colliculus of awake mouse generally show short latency, brisk responses. Receptive fields are usually ‘ON–OFF’ with a preference for black stimuli, and are weakly non‐linear in response to gratings and other forms of luminance modulation. Population responses to drifting gratings are highly contrast sensitive, with a robust response to spatial frequencies above 0.3 cycles degree−1 and temporal frequencies above 15 Hz. The receptive fields are also often speed‐tuned or direction‐selective. Analysis of the response across multiple stimulus dimensions reveals at least five functionally distinct groups of units. We also find that eye movements affect measurements of receptive field properties in awake animals, and show how these may be mitigated in analyses. Qualitatively similar responses were obtained in urethane‐anaesthetized animals, although receptive fields in awake animals had higher contrast sensitivity, shorter visual latency and a stronger response to high temporal frequencies.
Key points
In rodents, including mice, the superior colliculus is the major target of the retina, but its visual response is not well characterized.
In the present study, extracellular recordings from single nerve cells in the superficial layers of the superior colliculus were made in awake, head‐restrained mice, and their responses to visual stimuli were measured.
It was found that these neurons show brisk, highly sensitive and short latency visual responses, a preference for black over white stimuli, and diverse responses to moving patterns.
At least five broad classes can be defined by variation in functional properties among units.
The results of the present study demonstrate that eye movements have a measurable impact on visual responses in awake animals and show how they may be mitigated in analyses.
ATP-dependent chromatin remodellers modulate nucleosome dynamics by mobilizing or disassembling nucleosomes, as well as altering nucleosome composition. These chromatin remodellers generally function ...by translocating along nucleosomal DNA at the H3-H4 interface of nucleosomes. Here we show that, unlike other remodellers, INO80 translocates along DNA at the H2A-H2B interface of nucleosomes and persistently displaces DNA from the surface of H2A-H2B. DNA translocation and DNA torsional strain created near the entry site of nucleosomes by INO80 promotes both the mobilization of nucleosomes and the selective exchange of H2A.Z-H2B dimers out of nucleosomes and replacement by H2A-H2B dimers without any additional histone chaperones. We find that INO80 translocates and mobilizes H2A.Z-containing nucleosomes more efficiently than those containing H2A, partially accounting for the preference of INO80 to replace H2A.Z with H2A. Our data suggest that INO80 has a mechanism for dimer exchange that is distinct from other chromatin remodellers including its paralogue SWR1.
Clinical manifestations of cystic fibrosis (CF) result from an increase in the viscosity of the mucus secreted by epithelial cells that line the airways. Particle-tracking microrheology (PTM) is a ...widely accepted means of determining the viscoelastic properties of CF mucus, providing an improved understanding of this disease as well as an avenue to assess the efficacies of pharmacologic therapies aimed at decreasing mucus viscosity. Among its advantages, PTM allows the measurement of small volumes, which was recently utilized for an in situ study of CF mucus formed by airway cell cultures. Typically, particle tracks are obtained from fluorescence microscopy video images, although this limits one’s ability to distinguish particles by depth in a heterogeneous environment. Here, by performing PTM with high-resolution micro-optical coherence tomography (μOCT), we were able to characterize the viscoelastic properties of mucus, which enables simultaneous measurement of rheology with mucociliary transport parameters that we previously determined using μOCT. We obtained an accurate characterization of dextran solutions and observed a statistically significant difference in the viscosities of mucus secreted by normal and CF human airway cell cultures. We further characterized the effects of noise and imaging parameters on the sensitivity of μOCT-PTM by performing theoretical and numerical analyses, which show that our system can accurately quantify viscosities over the range that is characteristic of CF mucus. As a sensitive rheometry technique that requires very small fluid quantities, μOCT-PTM could also be generally applied to interrogate the viscosity of biological media such as blood or the vitreous humor of the eye in situ.
The use of remote sensing for monitoring chlorophyll-a (chla) and modelling eutrophication has advanced over the last decades. Although the application of the technology has proven successful in ...ocean ecosystems, there is a need to monitor chla concentrations in large, nutrient-poor inland water bodies. The main objective of this study was to explore the utility of publicly available remotely sensed Sentinel-2 (S2) imagery to quantify chla concentrations in the nutrient-deficient Lake Malawi/Niassa/Nyasa (LMNN). A secondary objective was to compare the S2 derived chla with the Global Change Observation Mission–Climate (GCOM-C) chla product that provides uninterrupted data throughout the year. In situ chla data (n = 76) from upper, middle and lower sections of LMNN served as a reference to produce remote sensing-based quantification. The line-height approach method built on color index, was applied for chla concentrations below 0.25 mg/m3. Moderate Resolution Imaging Spectroradiometer 3-band Ocean Color (MODIS-OC3) – was adopted when chla concentration exceeded 0.35 mg/m3. The MODIS-OC3 algorithm had generic model coefficients that were calibrated for each in situ sample by using GCOM-C Level 3 chla product. A weighted sum of the two algorithms was applied for chla concentrations that fell between 0.25 and 0.35 mg/m3. The above methods were then applied to the S2 data to estimate chla at each pixel. S2 showed a promising accuracy in distinguishing chla levels (MSE = 0.18) although the chla range in the lake was relatively narrow, particularly using the locally calibrated coefficients of the OC3 algorithm. Chla distribution maps produced from the S2 data revealed limited spatial variation across the LMNN with higher concentrations identified in the coastal areas. S2-derived chla and GCOM-C chla comparison showed fairly good similarity between the two datasets (MSE = 0.205). Accepting this similarity, monthly chla dynamics of the lake was profiled using the temporally reliable GCOM-C data that showed oligotrophic conditions (1.7 mg/m3 to 3.2 mg/m3) in most parts of the lake throughout the year. The study's findings advance the potential for both remote sensing approaches to provide vital information at the required spatial and temporal resolution for evidence-based policymaking and proactive environmental management in an otherwise very data deficient region.
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•Chlorophyll-a (chla) of oligotrophic LMNN was assessed using remote sensing.•High-resolution Sentinel-2 (S2) data estimated chla at promising accuracy levels.•Coarse-resolution GCOM-C chla product compared well with S2-derived chla.•Temporally-reliable GCOM-C chla product was used to profile monthly chla.•S2 and GCOM-C can be used to monitor chla in nutrient-deficient inland waters.
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