The role of the external ear in vertical sound localization in the free flying bat, Eptesicus fuscus

Impact of chitosan extracted from shrimp shells on the shrinkage and mechanical properties of cement-based composites using dendritic fibrous nanosilica

Dendritic fibrous nanosilica (DFNS) was functionalized using microcrystalline chitosan, derived from shrimp exoskeletons, to act as a robust anchor, resulting in DFNS@Chitosan. In order to prevent the restacking of chitosan sheets, the supramolecular polymerized chitosan not only served as a spacer but was also incorporated into cement-based composites. The physical-chemical characteristics of DFNS@Chitosan were assessed through various analytical techniques such as TEM, SEM, TGA, FTIR, AFM, XPS, and EDX. The potency and auto-induced contraction of Cement-based composite materials fortified with DFNS@Chitosan were probed. The incorporation of DFNS@Chitosan resulted in an increase in both compressive and interfacial stretching potency of the cement-based composites. Furthermore, the presence of DFNS@Chitosan effectively inhibited the occurrence of auto-induced contraction in the cement-based paste. This research endeavor is anticipated to promote an alternative utilization of DFNS and shrimp waste shells in the development of sustainable building materials.

Magnitude, Associated Risk Factors, and Trend Comparisons of Urinary Tract Infection among Pregnant Women and Diabetic Patients: A Systematic Review and Meta-Analysis

Urinary tract infection (UTI) remains the most common bacterial infection that affects millions of people around the world, especially pregnant women (PW) and people with diabetes mellitus (DM). This systematic review and meta-analysis was aimed at finding the pooled prevalence of UTI and its associated risk factors among PW and DM patients. Scientific articles written in English were recovered from PubMed, ScienceDirect, Web of Science, Google Scholar, Cochrane Library, Google Engine, and University Library Databases. "Prevalence," "urinary tract infection," "associated factors," "pregnant women," "diabetic patients," and "Ethiopia" were search terms used for this study. For critical appraisal, PRISMA-2009 was applied. Heterogeneity and publication bias were evaluated using Cochran's Q, inverse variance (I2), and funnel plot asymmetry tests. A random effect model was used to calculate the pooled prevalence of UTI and its associated factors among both patients, along with the parallel odds ratio (OR) and 95% confidence interval (CI). For this meta-analysis, a total of 7271 participants were included in the 25 eligible studies. The pooled prevalence of UTI in Ethiopia among both patients was 14.50% (95% CI: 13.02, 15.97), of which 14.21% (95% CI: 12.18, 16.25) and 14.75% (95% CI: 12.58, 16.92) were cases of DM and PW, respectively. According to the subgroup analysis, the highest prevalence was observed in the Oromia region (19.84%) and in studies conducted from 2018 to 2022 (14.68%). Being female (AOR: 0.88, and 95% CI: 0.11, 1.65, P = 0.01) and having an income level ≤ 500ETB (AOR: 4.46, and 95% CI: -1.19, 10.12, P = 0.03) were risk factors significantly associated with UTI among patients with DM and PW, respectively. Furthermore, a history of catheterization (AOR = 5.58 and 95% CI: 1.35, 9.81, P < 0.01), urinary tract infection (AOR: 3.52, and 95% CI: 1.96, 5.08, P < 0.01), and symptomatic patients (AOR: 2.32, and 95% CI: 0.57, 4.06, P < 0.01) were significantly associated with UTI in both patients. Early diagnosis and appropriate medication are necessary for the treatment of UTI in patients with DM and PW.

The continued importance of comparative auditory research to modern scientific discovery

A rich history of comparative research in the auditory field has afforded a synthetic view of sound information processing by ears and brains. Some organisms have proven to be powerful models for human hearing due to fundamental similarities (e.g., well-matched hearing ranges), while others feature intriguing differences (e.g., atympanic ears) that invite further study. Work across diverse "non-traditional" organisms, from small mammals to avians to amphibians and beyond, continues to propel auditory science forward, netting a variety of biomedical and technological advances along the way. In this brief review, limited primarily to tetrapod vertebrates, we discuss the continued importance of comparative studies in hearing research from the periphery to central nervous system with a focus on outstanding questions such as mechanisms for sound capture, peripheral and central processing of directional/spatial information, and non-canonical auditory processing, including efferent and hormonal effects.

Insights into organoid-based modeling of COVID-19 pathology

Since December 2019, various types of strategies have been applied due to the emergent need to investigate the biology and pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to discover a functional treatment. Different disease modeling systems, such as mini-organ technology, have been used to improve our understanding of SARS-CoV-2 physiology and pathology. During the past 2 years, regenerative medicine research has shown the supportive role of organoid modeling in controlling coronavirus disease 2019 (COVID-19) through optimal drug and therapeutic approach improvement. Here, we overview some efforts that have been made to study SARS-CoV-2 by mimicking COVID-19 using stem cells. In addition, we summarize a perspective of drug development in COVID-19 treatment via organoid-based studies.

New reports of morphological anomalies in leaf-nosed bats (Chiroptera: Phyllostomidae) from Colombia

Morphological anomalies in bats are rarely reported. We present new reports of three types of morphological anomalies (chromatic, wing, and ear) from specimens in a biological collection and from individuals captured during field sampling. We recorded piebaldism on seven individuals from six species: Carollia perspicillata, Glossophaga commissarisi, Hsunycteris thomasi, Phyllostomus elongatus, and Trachops cirrhosus from Guaviare collected in 2022, and Tonatia saurophila from Casanare collected in 2020. These represent three new reports for the continent (P. elongatus, G. commissarisi, and H. thomasi). We also recorded the broken digits anomaly on two individuals from two species: Platyrrhinus sp. and Sturnira sp. from Chocó collected in 2019. In addition, we found one case of the absence of pinnae and tragus in C. perspicillata from Santander collected in 2018; an absence not previously reported in bats. We encourage researchers to report their observations of bats with morphological anomalies, as this information could be useful in estimating occurrence rates and addressing questions about its effects on populations.

Neural Processing of Naturalistic Echolocation Signals in Bats

Echolocation behavior, a navigation strategy based on acoustic signals, allows scientists to explore neural processing of behaviorally relevant stimuli. For the purpose of orientation, bats broadcast echolocation calls and extract spatial information from the echoes. Because bats control call emission and thus the availability of spatial information, the behavioral relevance of these signals is undiscussable. While most neurophysiological studies, conducted in the past, used synthesized acoustic stimuli that mimic portions of the echolocation signals, recent progress has been made to understand how naturalistic echolocation signals are encoded in the bat brain. Here, we review how does stimulus history affect neural processing, how spatial information from multiple objects and how echolocation signals embedded in a naturalistic, noisy environment are processed in the bat brain. We end our review by discussing the huge potential that state-of-the-art recording techniques provide to gain a more complete picture on the neuroethology of echolocation behavior.

Quantifying intracellular trafficking of silica-coated magnetic nanoparticles in live single cells by site-specific direct stochastic optical reconstruction microscopy

Background

Nanoparticles have been used for biomedical applications, including drug delivery, diagnosis, and imaging based on their unique properties derived from small size and large surface-to-volume ratio. However, concerns regarding unexpected toxicity due to the localization of nanoparticles in the cells are growing. Herein, we quantified the number of cell-internalized nanoparticles and monitored their cellular localization, which are critical factors for biomedical applications of nanoparticles.

Methods

This study investigates the intracellular trafficking of silica-coated magnetic nanoparticles containing rhodamine B isothiocyanate dye [MNPs@SiO₂(RITC)] in various live single cells, such as HEK293, NIH3T3, and RAW 264.7 cells, using site-specific direct stochastic optical reconstruction microscopy (dSTORM). The time-dependent subdiffraction-limit spatial resolution of the dSTORM method allowed intracellular site-specific quantification and tracking of MNPs@SiO₂(RITC).

Results

The MNPs@SiO₂(RITC) were observed to be highly internalized in RAW 264.7 cells, compared to the HEK293 and NIH3T3 cells undergoing single-particle analysis. In addition, MNPs@SiO₂(RITC) were internalized within the nuclei of RAW 264.7 and HEK293 cells but were not detected in the nuclei of NIH3T3 cells. Moreover, because of the treatment of the MNPs@SiO₂(RITC), more micronuclei were detected in RAW 264.7 cells than in other cells.

Conclusion

The sensitive and quantitative evaluations of MNPs@SiO₂(RITC) at specific sites in three different cells using a combination of dSTORM, transcriptomics, and molecular biology were performed. These findings highlight the quantitative differences in the uptake efficiency of MNPs@SiO₂(RITC) and ultra-sensitivity, varying according to the cell types as ascertained by subdiffraction-limit super-resolution microscopy.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01147-1.

Deafness in an auditory specialist, the big brown bat (Eptesicus fuscus)

Bats are long-lived animals that show presumed resistance to noise-induced and age-related hearing loss, which has been attributed to their dependence on sound processing for survival. Echolocation and basic auditory functions have been studied extensively in the big brown bat (Eptesicus fuscus), an insectivorous microchiropteran species. We conducted hearing tests and analysis of cochlear sensory cells in a group of big brown bats that exhibited anomalies in behavioral sonar tracking experiments and/or lacked neural responses to acoustic stimulation in subcortical auditory nuclei. We show for the first time the presence of profound deafness and extensive cochlear damage in an echolocating bat species. Auditory brainstem responses were abnormal or absent in these bats, and histological analyses of their cochleae revealed extensive loss of hair cells, supporting cells, and spiral ganglion neurons. The underlying cause of deafness is unknown.

Efficient encoding of spectrotemporal information for bat echolocation

In most animals, natural stimuli are characterized by a high degree of redundancy, limiting the ensemble of ecologically valid stimuli to a significantly reduced subspace of the representation space. Neural encodings can exploit this redundancy and increase sensing efficiency by generating low-dimensional representations that retain all information essential to support behavior. In this study, we investigate whether such an efficient encoding can be found to support a broad range of echolocation tasks in bats. Starting from an ensemble of echo signals collected with a biomimetic sonar system in natural indoor and outdoor environments, we use independent component analysis to derive a low-dimensional encoding of the output of a cochlear model. We show that this compressive encoding retains all essential information. To this end, we simulate a range of psycho-acoustic experiments with bats. In these simulations, we train a set of neural networks to use the encoded echoes as input while performing the experiments. The results show that the neural networks’ performance is at least as good as that of the bats. We conclude that our results indicate that efficient encoding of echo information is feasible and, given its many advantages, very likely to be employed by bats. Previous studies have demonstrated that low-dimensional encodings allow for task resolution at a relatively high level. In contrast to previous work in this area, we show that high performance can also be achieved when low-dimensional filters are derived from a data set of realistic echo signals, not tailored to specific experimental conditions.

We show that complex (and simple) echoes from real environments can be efficiently and effectively represented using a small set of filters. Critically, we show that high performance across a range of tasks can be achieved when low-dimensional filters are derived from a data set of realistic echo signals, not tailored to specific experimental conditions. The redundancy in echoic information opens up the opportunity for efficient encoding, reducing the computational load of echo processing as well as the memory load for storing the information. Therefore, we predict the auditory system of bats to capitalize on this opportunity for efficient coding by implementing filters with spectrotemporal properties akin to those hypothesized here. Indeed, the filters we obtain here are similar to those found in other animals and other sensing capabilities. Our results indicate that bats could exploit the redundancy in sonar signals to implement an efficient neural encoding of the relevant information.

Special acoustical role of pinna simplifying spatial target localization by the brown long-eared bat Plecotus auritus

Echolocating bats locate a target by sonar. The performance of this system is related to the shape of the binaural conformation in bats. From numerical predictions, it was found that in a central frequency band, the orientation of a strong sidelobe is shifted nearly linearly in the vertical direction. Inspired by this, the authors built an accurate wide-scope elevation estimation system by constructing a pair of erect artificial pinnae and realized simultaneous elevation and azimuth estimation by constructing a pair of orthogonal pinnae. By demonstrating the simplicity of spatial target echolocation, the authors showed that only two independent single-output neural networks were needed for either elevation or azimuth estimation. This method could be applied to imitate any other mammal species with similar pinna directivity patterns to facilitate and improve an artificial echolocation system.

Assessing the genetic relationships between osteoarthritis and human plasma proteins: a large scale genetic correlation scan

Background

Osteoarthritis (OA) is a multifactorial complex disease. The impact of plasma proteins on OA remains elusive now.

Methods

The UK Biobank genome-wide association study data of OA was used here. Genome-wide SNP genotyping was performed using the Affymetrix UK BiLEVE Axiom or UK Biobank Axiom array. Equally, the GWAS summary data of 3,622 plasma proteins was derived from a recently published study. Consequently, linkage disequilibrium score regression (LD score regression) analysis was performed to evaluate the genetic correlation between each plasma protein and different sites of OA.

Results

Several suggestive plasma proteins were identified for OA. For hand OA, evidence of genetic correlation was observed for inter-alpha-trypsin inhibitor heavy chain H1 (coefficient =−0.3854, P value =0.0198), multiple inositol polyphosphate phosphatase 1 (coefficient =−1.1721, P value =0.0303). For hip OA, 7 suggestive genetic correlation signals were observed, such as Transmembrane glycoprotein NMB (coefficient =0.6944, P value =0.0098), Endothelial cell-specific molecule 1 (coefficient =0.6337, P value =0.03). For Knee OA, 12 suggestive genetic correlation signals were identified, including Elafin (coefficient =−0.5562, P value =0.0092), Interleukin-16 (coefficient =0.3949, P value =0.0435).

Conclusions

We investigated the genetic correlations between plasma proteins and different sites of OA in a systematic way. Our results provide novel evidence that OA is a heterogeneous disease.

Adaptive Echolocation and Flight Behaviors in Bats Can Inspire Technology Innovations for Sonar Tracking and Interception

Target tracking and interception in a dynamic world proves to be a fundamental challenge faced by both animals and artificial systems. To track moving objects under natural conditions, agents must employ strategies to mitigate interference and conditions of uncertainty. Animal studies of prey tracking and capture reveal biological solutions, which can inspire new technologies, particularly for operations in complex and noisy environments. By reviewing research on target tracking and interception by echolocating bats, we aim to highlight biological solutions that could inform new approaches to artificial sonar tracking and navigation systems. Most bat species use wideband echolocation signals to navigate dense forests and hunt for evasive insects in the dark. Importantly, bats exhibit rapid adaptations in flight trajectory, sonar beam aim, and echolocation signal design, which appear to be key to the success of these animals in a variety of tasks. The rich suite of adaptive behaviors of echolocating bats could be leveraged in new sonar tracking technologies by implementing dynamic sensorimotor feedback control of wideband sonar signal design, head, and ear movements.

Synthesis of benzimidazolones by immobilized gold nanoparticles on chitosan extracted from shrimp shells supported on fibrous phosphosilicate

We demonstrate the synthesis of benzimidazolones from o-phenylenediamines and CO₂ in the presence of gold nanoparticles supported on a composite material based on microcrystalline chitosan from shrimp shells and fibrous phosphosilicate.

Modeling bat prey capture in echolocating bats: The feasibility of reactive pursuit

Echolocating bats are the only mammals engaging in airborne pursuit. In this paper, we implement a reactive model of sonar based prey pursuit in bats. Our simulations include a realistic prey localization mechanism as well as a model of the bat's motor behavior. In contrast to previous work, our model incorporates bats' ability to execute rapid saccadic scanning motions keeping the prey within its field of view. Decoupling the flight direction from the gaze direction allows our model to capture erratically moving prey using reactive control. We conclude that the rapid shifts in gaze direction allow bats to deal with the narrow field of view provided by their sonar system.

Overexpression of adiponectin alleviates intracerebral hemorrhage-induced brain injury in rats via suppression of oxidative stress

Oxidative stress and blood-brain barrier (BBB) dysfunction contribute to brain injury after intracerebral hemorrhage (ICH). Adiponectin (APN) inhibits oxidative stress in the CNS, but the role of APN in ICH is not clear. Thus, we elucidated the possible neuroprotective effect of APN in ICH-induced brain injury in rats and investigated the neuroprotective mechanisms. A lentivirus-carrying APN gene was injected into rats 14 days before ICH induced via intracerebral injection of autologous blood. The effects of lentiviral overexpression of APN on brain injury were evaluated 24 h after ICH. Superoxide dismutase (SOD), glutathione (GSH), and the ratio of oxidized glutathione to reduced glutathione (GSSG/GSH) and malondialdehyde (MDA) were measured. Oxidative stress-related proteins were measured by Western blot and qRT-PCR. APN overexpression improved neurological function, reduced brain edema, preserved the BBB and increased the expression of APN and decreased the expression of NADPH oxidase-2 (NOX 2) compared with null vector controls (p < 0.01). SOD, GSH, and GSSG/GSH increased, and MDA was reduced. Furthermore, tetrabromocinnamic acid (TBCA, a NADPH oxidase activator) blocked the effect of APN on cerebral protection and antioxidant activity. Our results demonstrate the importance of APN in regulating oxidative stress and BBB function and suggest APN may be a novel treatment for brain damage after ICH.

Echo-acoustic scanning with noseleaf and ears in phyllostomid bats

The mammalian visual system is highly directional and mammals typically employ rapid eye movements to scan their environment. Both sound emission and hearing in echolocating bats are directional but not much is known about how bats use ear movements and possibly movements of the sound-emitting structures to scan space. Here, we investigated in a tightly controlled behavioural experiment how Phyllostomusdiscolor bats employ their echolocation system while being moved through differently structured environments: we monitored and reconstructed both a close-up of the facial structures in 3D, including the motile noseleaf and outer ears, and the sonar-beam of the bat while it was moved along reflectors. Despite the simple linear movement of the bats in the setup, the bats pointed their beam quite variably in azimuth with a standard deviation of about ±20 deg. This variation arises from yaw-type head rotations. Video analyses show that the bat's noseleaf twitches with every echolocation call. Second, we show that the bat's ears are raised to a rather stereotypical head-centred position with every echolocation call. Surprisingly, P. discolor can adjust the timing and the magnitude of these ear movements to the distance of the reflectors with millisecond precision. Our findings reveal echolocation-specific specialisations as well as general principles of scanning and stabilisation of a directional remote sense. The call-correlated movements of the facial structures may lead to a higher directionality of the echolocation system and may enable the bats to adjust their echo-acoustic gaze to dynamic environments.

Sensorimotor Model of Obstacle Avoidance in Echolocating Bats

Bat echolocation is an ability consisting of many subtasks such as navigation, prey detection and object recognition. Understanding the echolocation capabilities of bats comes down to isolating the minimal set of acoustic cues needed to complete each task. For some tasks, the minimal cues have already been identified. However, while a number of possible cues have been suggested, little is known about the minimal cues supporting obstacle avoidance in echolocating bats. In this paper, we propose that the Interaural Intensity Difference (IID) and travel time of the first millisecond of the echo train are sufficient cues for obstacle avoidance. We describe a simple control algorithm based on the use of these cues in combination with alternating ear positions modeled after the constant frequency bat Rhinolophus rouxii. Using spatial simulations (2D and 3D), we show that simple phonotaxis can steer a bat clear from obstacles without performing a reconstruction of the 3D layout of the scene. As such, this paper presents the first computationally explicit explanation for obstacle avoidance validated in complex simulated environments. Based on additional simulations modelling the FM bat Phyllostomus discolor, we conjecture that the proposed cues can be exploited by constant frequency (CF) bats and frequency modulated (FM) bats alike. We hypothesize that using a low level yet robust cue for obstacle avoidance allows bats to comply with the hard real-time constraints of this basic behaviour.

Echolocating bats can fly through complex environments in complete darkness. Swift and apparently effortless obstacle avoidance is the most fundamental function supported by biosonar. Despite this, we still do not know which acoustic cues, from among the many possible cues, bats actually exploit while avoiding obstacles. In this paper, we show using spatial simulations (2D and 3D) that the Interaural Intensity Difference (IID) and travel time of the first millisecond of the echo train in combination with alternating ear positions provide robust and reliable cues for obstacle avoidance. Simulating the echoes received by a flying bat, we show that simple phonotaxis can steer a bat clear from obstacles without performing 3D reconstruction of the layout of the scene. As such, this paper presents the first computationally explicit explanation for obstacle avoidance in realistic and complex 3D environments. We hypothesize that using low level yet robust cues for obstacle avoidance allows bats to comply with the hard real-time constraints of this basic behaviour.

Features in geometric receiver shapes modelling bat-like directivity patterns

The directional properties of bat ears as receivers is a current area of interest in ultrasound research. This paper presents a new approach to analyse the relationship between morphological features and acoustical properties of the external ear of bat species. The beam pattern of Rousettus leschenaultii's right ear is measured and compared to that of receiver structures whose design is inspired by the bat ear itself and made of appropriate geometric shapes. The regular shape of these receivers makes it possible to control the key reception parameters and thus to understand the effect on the associated beam pattern of the parameters themselves. Measurements show one receiver structure has a beam pattern very similar to that of R. leschenaultii's ear, thus explaining the function of individual parts constituting its ear. As it is applicable to all bat species, this approach can provide a useful tool to investigate acoustics in bats, and possibly other mammals.

A Device for Human Ultrasonic Echolocation

OBJECTIVE

We present a device that combines principles of ultrasonic echolocation and spatial hearing to provide human users with environmental cues that are 1) not otherwise available to the human auditory system, and 2) richer in object and spatial information than the more heavily processed sonar cues of other assistive devices. The device consists of a wearable headset with an ultrasonic emitter and stereo microphones with affixed artificial pinnae. The goal of this study is to describe the device and evaluate the utility of the echoic information it provides.

METHODS

The echoes of ultrasonic pulses were recorded and time stretched to lower their frequencies into the human auditory range, then played back to the user. We tested performance among naive and experienced sighted volunteers using a set of localization experiments, in which the locations of echo-reflective surfaces were judged using these time-stretched echoes.

RESULTS

Naive subjects were able to make laterality and distance judgments, suggesting that the echoes provide innately useful information without prior training. Naive subjects were generally unable to make elevation judgments from recorded echoes. However, trained subjects demonstrated an ability to judge elevation as well.

CONCLUSION

This suggests that the device can be used effectively to examine the environment and that the human auditory system can rapidly adapt to these artificial echolocation cues.

SIGNIFICANCE

Interpreting and interacting with the external world constitutes a major challenge for persons who are blind or visually impaired. This device has the potential to aid blind people in interacting with their environment.

The aerodynamic cost of head morphology in bats: maybe not as bad as it seems

At first sight, echolocating bats face a difficult trade-off. As flying animals, they would benefit from a streamlined geometric shape to reduce aerodynamic drag and increase flight efficiency. However, as echolocating animals, their pinnae generate the acoustic cues necessary for navigation and foraging. Moreover, species emitting sound through their nostrils often feature elaborate noseleaves that help in focussing the emitted echolocation pulses. Both pinnae and noseleaves reduce the streamlined character of a bat's morphology. It is generally assumed that by compromising the streamlined charactered of the geometry, the head morphology generates substantial drag, thereby reducing flight efficiency. In contrast, it has also been suggested that the pinnae of bats generate lift forces counteracting the detrimental effect of the increased drag. However, very little data exist on the aerodynamic properties of bat pinnae and noseleaves. In this work, the aerodynamic forces generated by the heads of seven species of bats, including noseleaved bats, are measured by testing detailed 3D models in a wind tunnel. Models of Myotis daubentonii, Macrophyllum macrophyllum, Micronycteris microtis, Eptesicus fuscus, Rhinolophus formosae, Rhinolophus rouxi and Phyllostomus discolor are tested. The results confirm that non-streamlined facial morphologies yield considerable drag forces but also generate substantial lift. The net effect is a slight increase in the lift-to-drag ratio. Therefore, there is no evidence of high aerodynamic costs associated with the morphology of bat heads.

Diabetic retinopathy: variations in patient therapeutic outcomes and pharmacogenomics

Diabetes and its microvascular complications in patients poses a significant challenge and constitutes a major health problem. When it comes to manifestations in the eye, each case of diabetic retinopathy (DR) is unique, in terms of the phenotype, genotype, and, more importantly, the therapeutic response. It is therefore important to identify factors that distinguish one patient from another. Personalized therapy in DR is a new trend aimed at achieving maximum therapeutic response in patients by identifying genotypic and phenotypic factors that may result in less than optimal response to conventional therapy, and consequently, lead to poorer outcome. With advances in the identification of these genetic markers, such as gene polymorphisms and human leucocyte antigen associations, as well as development of drugs that can target their effects, the future of personalized medicine in DR is promising. In this comprehensive review, data from various studies have been analyzed to present what has been achieved in the field of pharmacogenomics thus far. An insight into future research is also provided.

Biosonar navigation above water I: estimating flight height

Locomotion and foraging on the wing require precise navigation in more than just the horizontal plane. Navigation in three dimensions and, specifically, precise adjustment of flight height are essential for flying animals. Echolocating bats drink from water surfaces in flight, which requires an exceptionally precise vertical navigation. Here, we exploit this behavior in the bat, Phyllostomus discolor, to understand the biophysical and neural mechanisms that allow for sonar-guided navigation in the vertical plane. In a set of behavioral experiments, we show that for echolocating bats, adjustment of flight height depends on the tragus in their outer ears. Specifically, the tragus imposes elevation-specific spectral interference patterns on the echoes of the bats' sonar emissions. Head-related transfer functions of our bats show that these interference patterns are most conspicuous in the frequency range ∼55 kHz. This conspicuousness is faithfully preserved in the frequency tuning and spatial receptive fields of cortical single and multiunits recorded from anesthetized animals. In addition, we recorded vertical spatiotemporal response maps that describe neural tuning in elevation over time. One class of units that were very sharply tuned to frequencies ∼55 kHz showed unusual spatiotemporal response characteristics with a preference for paired echoes where especially the first echo originates from very low elevations. These behavioral and neural data provide the first insight into biosonar-based processing and perception of acoustic elevation cues that are essential for bats to navigate in three-dimensional space.

Advances in self-assembled chitosan nanomaterials for drug delivery

Nanomaterials based on chitosan have emerged as promising carriers of therapeutic agents for drug delivery due to good biocompatibility, biodegradability, and low toxicity. Chitosan originated nanocarriers have been prepared by mini-emulsion, chemical or ionic gelation, coacervation/precipitation, and spray-drying methods. As alternatives to these traditional fabrication methods, self-assembled chitosan nanomaterials show significant advantages and have received growing scientific attention in recent years. Self-assembly is a spontaneous process by which organized structures with particular functions and properties could be obtained without additional complicated processing or modification steps. In this review, we focus on recent progress in the design, fabrication and physicochemical aspects of chitosan-based self-assembled nanomaterials. Their applications in drug delivery of different therapeutic agents are also discussed in details.

Dominant glint based prey localization in horseshoe bats: a possible strategy for noise rejection

Rhinolophidae or Horseshoe bats emit long and narrowband calls. Fluttering insect prey generates echoes in which amplitude and frequency shifts are present, i.e. glints. These glints are reliable cues about the presence of prey and also encode certain properties of the prey. In this paper, we propose that these glints, i.e. the dominant glints, are also reliable signals upon which to base prey localization. In contrast to the spectral cues used by many other bats, the localization cues in Rhinolophidae are most likely provided by self-induced amplitude modulations generated by pinnae movement. Amplitude variations in the echo not introduced by the moving pinnae can be considered as noise interfering with the localization process. The amplitude of the dominant glints is very stable. Therefore, these parts of the echoes contain very little noise. However, using only the dominant glints potentially comes at a cost. Depending on the flutter rate of the insect, a limited number of dominant glints will be present in each echo giving the bat a limited number of sample points on which to base localization. We evaluate the feasibility of a strategy under which Rhinolophidae use only dominant glints. We use a computational model of the echolocation task faced by Rhinolophidae. Our model includes the spatial filtering of the echoes by the morphology of the sonar apparatus of Rhinolophus rouxii as well as the amplitude modulations introduced by pinnae movements. Using this model, we evaluate whether the dominant glints provide Rhinolophidae with enough information to perform localization. Our simulations show that Rhinolophidae can use dominant glints in the echoes as carriers for self-induced amplitude modulations serving as localization cues. In particular, it is shown that the reduction in noise achieved by using only the dominant glints outweighs the information loss that occurs by sampling the echo.

Rhinolophidae are echolocating bats that hunt among vegetation. The foliage returns clutter echoes that potentially mask the echoes of insect prey. However, prey introduces frequency and amplitude shifts, called glints, into the echo to which these bats are highly sensitive. Therefore, these glints are used by Rhinolophidae to detect prey and infer its properties. One of the defining characteristic of consecutive dominant glints is that they have a very stable amplitude. This is, consecutive wing beats of the insect produce dominant glints with more of less the same amplitude. Owing to the strategy Rhinolophidae use to locate prey, the stable amplitude of glints makes these parts of the echoes ideal signals to use to locate prey. In this paper, we demonstrate the feasibility of strategy under which Rhinolophidae use only the dominant glints in the echo for locating prey.

Information generated by the moving pinnae of Rhinolophus rouxi: tuning of the morphology at different harmonics

Bats typically emit multi harmonic calls. Their head morphology shapes the emission and hearing sound fields as a function of frequency. Therefore, the sound fields are markedly different for the various harmonics. As the sound field provides bats with all necessary cues to locate objects in space, different harmonics might provide them with variable amounts of information about the location of objects. Also, the ability to locate objects in different parts of the frontal hemisphere might vary across harmonics. This paper evaluates this hypothesis in R. rouxi, using an information theoretic framework. We estimate the reflector position information transfer in the echolocation system of R. rouxi as a function of frequency. This analysis shows that localization performance reaches a global minimum and a global maximum at the two most energetic frequency components of R. rouxi call indicating tuning of morphology and harmonic structure. Using the fundamental the bat is able to locate objects in a large portion of the frontal hemisphere. In contrast, using the 1 overtone, it can only locate objects, albeit with a slightly higher accuracy, in a small portion of the frontal hemisphere by reducing sensitivity to echoes from outside this region of interest. Hence, different harmonic components provide the bat either with a wide view or a focused view of its environment. We propose these findings can be interpreted in the context of the foraging behaviour of R. rouxi, i.e., hunting in cluttered environments. Indeed, the focused view provided by the 1 overtone suggests that at this frequency its morphology is tuned for clutter rejection and accurate localization in a small region of interest while the finding that overall localization performance is best at the fundamental indicates that the morphology is simultaneously tuned to optimize overall localization performance at this frequency.

Numerical analysis of biosonar beamforming mechanisms and strategies in bats

Beamforming is critical to the function of most sonar systems. The conspicuous noseleaf and pinna shapes in bats suggest that beamforming mechanisms based on diffraction of the outgoing and incoming ultrasonic waves play a major role in bat biosonar. Numerical methods can be used to investigate the relationships between baffle geometry, acoustic mechanisms, and resulting beampatterns. Key advantages of numerical approaches are: efficient, high-resolution estimation of beampatterns, spatially dense predictions of near-field amplitudes, and the malleability of the underlying shape representations. A numerical approach that combines near-field predictions based on a finite-element formulation for harmonic solutions to the Helmholtz equation with a free-field projection based on the Kirchhoff integral to obtain estimates of the far-field beampattern is reviewed. This method has been used to predict physical beamforming mechanisms such as frequency-dependent beamforming with half-open resonance cavities in the noseleaf of horseshoe bats and beam narrowing through extension of the pinna aperture with skin folds in false vampire bats. The fine structure of biosonar beampatterns is discussed for the case of the Chinese noctule and methods for assessing the spatial information conveyed by beampatterns are demonstrated for the brown long-eared bat.

What noseleaves do for FM bats depends on their degree of sensorial specialization

Background

Many bats vocalizing through their nose carry a prominent noseleaf that is involved in shaping the emission beam of these animals. To our knowledge, the exact role of these appendages has not been thoroughly investigated as for no single species both the hearing and the emission spatial sensitivities have been obtained. In this paper, we set out to evaluate the complete spatial sensitivity of two species of New World leaf-nosed bats: Micronycteris microtis and Phyllostomus discolor. From an ecological point of view, these species are interesting as they belong to the same family (Phyllostomidae) and their noseleaves are morphologically similar. They differ vastly in the niche they occupy. Comparing these species allows us to relate differences in function of the noseleaf to the ecological background of bat species.

Methodology/Principal Findings

We simulate the spatial sensitivity of both the hearing and the emission subsystems of two species, M. microtis and P. discolor. This technique allows us to evaluate the respective roles played by the noseleaf in the echolocation system of these species. We find that the noseleaf of M. microtis focuses the radiated energy better and yields better control over the emission beam.

Conclusions

From the evidence presented we conclude that the noseleaves serve quantitatively different functions for different bats. The main function of the noseleaf is to serve as an energy focusing mechanism that increases the difference between the reflected energy from objects in the focal area and objects in the periphery. However, despite the gross morphological similarities between the noseleaves of the two Phyllostomid species they focus the energy to a different extent, a capability that can be linked to the different ecological niches occupied by the two species.

Bat echolocation processing using first-spike latency coding

To perform echolocation, so-called FM-bats emit short pulses i.e., with a duration of a few milliseconds, and analyse the echoes coming from their environment. One individual echo, due to its short duration, will cause neurons in the early auditory system to generate between 1 and 3 spikes only. Hence, we argue that it is advantageous for FM-bats to use spike-time rather that firing rate information. We present a simple spike-time model of the monaural and binaural pathways up to the midbrain, to show that spike-time information can indeed be processed by the known neural architecture. In particular, we show that a First Spike Latency (FSL) code, as provided by the auditory nerves, can represent both the monaural and binaural intensity cues induced by the head-related transfer function in the peripheral system. We also show that ascending centres enhance the cues conveyed by such an FSL code. Finally, we present experimental results, comparing the FSL code based model proposed here with a more classic firing rate code, and we show that first-spike latency is a more biologically plausible alternative.

Sound-diffracting flap in the ear of a bat generates spatial information

Sound diffraction by the mammalian ear generates source-direction information. We have obtained an immediate quantification of this information from numerical predictions. We demonstrate the power of our approach by showing that a small flap in a bat's pinna generates useful information over a large set of directions in a central band of frequencies: presence of the flap more than doubled the solid angle with direction information above a given threshold. From the workings of the employed information measure, the Cramér-Rao lower bound, we can explain how physical shape is linked to sensory information via a strong sidelobe with frequency-dependent orientation in the directivity pattern. This method could be applied to any other mammal species with pinnae to quantify the relative importance of pinna structures' contributions to directional information and to facilitate interspecific comparisons of pinna directivity patterns.

Pressure difference receiving ears

Directional sound receivers are useful for locating sound sources, and they can also partly compensate for the signal degradations caused by noise and reverberations. Ears may become inherently directional if sound can reach both surfaces of the eardrum. Attempts to understand the physics of such pressure difference receiving ears have been hampered by lack of suitable experimental methods. In this review, we review the methods for collecting reliable data on the binaural directional cues at the eardrums, on how the eardrum vibrations depend on the direction of sound incidence, and on how sound waves behave in the air spaces leading to the interior surfaces of eardrums. A linear mathematical model with well-defined inputs is used for exploring how the directionality varies with the binaural directional cues and the amplitude and phase gain of the sound pathway to the inner surface of the eardrum. The mere existence of sound transmission to the inner surface does not ensure a useful directional hearing, since a proper amplitude and phase relationship must exist between the sounds acting on the two surfaces of the eardrum. The gain of the sound pathway must match the amplitude and phase of the sounds at the outer surfaces of the eardrums, which are determined by diffraction and by the arrival time of the sound, that is by the size and shape of the animal and by the frequency of sound. Many users of hearing aids do not obtain a satisfactory improvement of their ability to localize sound sources. We suggest that some of the mechanisms of directional hearing evolved in Nature may serve as inspiration for technical improvements.

Numerical study of the effect of the noseleaf on biosonar beamforming in a horseshoe bat

Around 300 bat species are known to emit their ultrasonic biosonar pulses through the nostrils. This nasal emission coincides with the presence of intricately shaped baffle structures surrounding the nostrils. Some prior experimental evidence indicates that these "noseleaves" have an effect on the shape of the animals' radiation patterns. Here, we present a numerical acoustical analysis of the noseleaf of a horseshoe bat species. We show that all three distinctive parts of its noseleaf ("lancet," "sella," "anterior leaf") have an effect on the acoustic near field as well as on the directivity pattern. Furthermore, we show that furrows in one of the parts (the lancet) also exert such an influence. The underlying physical mechanisms suggested by the properties of the estimated near field are cavity resonance, as well as reflection and shadowing of the sound waves emitted by the nostrils. In their effects on the near field, the noseleaf parts showed a tendency toward spatial partitioning with the effects due to each part dominating a certain region. However, interactions between the acoustic effects of the parts were also evident, most notably, a synergism between two frequency-dependent effects (cavity resonance and shadowing) to produce an even stronger frequency selectivity.