Weak Stimuli Research Articles

A receptor-inactivation model for single-celled habituation in Stentor coeruleus.

The single-celled ciliate Stentor coeruleus demonstrates habituation to mechanical stimuli, showing that even single cells can manifest a basic form of learning. Although the ability of Stentor to habituate has been extensively documented, the mechanism of learning is currently not known. Here we take a bottom-up approach and investigate a simple biochemistry-based model based on prior electrophysiological measurements in Stentor along with general properties of receptor molecules. In this model, a mechanoreceptor senses the stimulus and leads to channel opening to change membrane potential, with a sufficient change in polarization triggering an action potential that drives contraction. Receptors that are activated can become internalized, after which they can either be degraded or recycled back to the cell surface. This activity-dependent internalization provides a potential means for the cell to learn. Stochastic simulations of this model confirm that it is capable of showing habituation similar to what is seen in actual Stentor cells, including the lack of dishabituation by strong stimuli and the apparently step-like response of individual cells during habituation. The model also can account for several habituation hallmarks that a previous two-state Markov model could not, namely, the dependence of habituation rate on stimulus magnitude, which had to be added onto the two state model but arises naturally in the receptor inactivation model; the rate of response recovery after cessation of stimulation; the ability of high frequency stimulus sequences to drive faster habituation that results in a lower response probability, and the potentiation of habituation by repeated rounds of training and recovery. The model makes the prediction that application of high force stimuli that do not normally habituate should drive habituation to weaker stimuli due to decrease in the receptor number, which serves as an internal hidden variable. We confirmed this prediction using two new sets of experiments involving alternation of weak and strong stimuli. Furthermore, the model predicts that training with high force stimuli delays response recovery to low force stimuli, which aligns with our new experimental data. The model also predicts subliminal accumulation, wherein continuation of training even after habituation has reached asymptotic levels should lead to delayed response recovery, which was also confirmed by new experiments. The model is unable to account for the phenomenon of rate sensitivity, in which habituation caused by higher frequency stimuli is more easily reversed leading to a frequency dependence of response recovery. Such rate sensitivity has not been reported in Stentor . Here we carried out a new set of experiments which are consistent with the model's prediction of the lack of rate sensitivity. This work demonstrates how a simple model can suggest new ways to probe single-cell learning at an experimental level. Finally, we interpret the model in terms of a kernel estimator that the cell may use to guide its decisions about how to response to new stimuli as they arise based on information, or the lack thereof, from past stimuli.

Efficient Thermo-Optic Switching and Modulating in Nonlocal Metasurfaces.

High-Q optical resonances in nonlocal metasurfaces, benefiting from significantly enhanced light/matter interactions, feature strong responses even under a weak external stimulus. In this work, we leverage the high-Q resonances of quasi-guided modes (QGMs) supported by a photonic crystal slab (PCS) structure to achieve efficient optical switching/modulation. The QGMs with an experimentally measured Q-factor of ∼2200 are realized by shifting every second column of air holes in a rectangular lattice within a silicon slab. At a weak illumination intensity of less than 4.0 W/cm2 from a 532 nm continuous-wave pump laser, the QGM resonance around 1550 nm experiences a pronounced spectral shift, with modulation depth exceeding 55%. This is attributed to the thermo-optic response caused by photothermal heating of the metasurface triggered by the absorption of the pump laser in silicon, which is further verified by the electrical heating approach. Our reported results showcase a simple yet effective way of tailoring light propagation in nonlocal metasurfaces.

La pratique du cyclisme de haut niveau impacte-t-elle la masse osseuse ?

Background : Elite cyclists may be at risk for osteopenia. Many factors can lead to bone loss in cycling, including low energy availability, low grade of inflammation, and a weak mechanical osteogenic stimulus. Thus we wanted to assess bone health in one elite team of professional cyclists, and to identify correlations between BMD and potential risks factors.Methods : Thirty-three adult male cyclists were recruited from one international team. Total body, hip femur and lumbar spine BMD had been measured by DXA and was compared to standard values for a healthy population of same age and sex. Training characteristics, morphometrics, body lean mass, fat mass, history, medication and results of recent blood and stool analysis were collected and compared between the cyclists having low BMD and those with unaltered BMD. Univariate and multivariate correlation analyses were carried out to identify predictive factors for low BMD.Results : Twenty-one (64%) out of 33 cyclists presented a Z score < -1 at one site, and five of them (15%) had densitometric osteoporosis. Lumbar spine was involved every time ‘Z score = -b 1,23 +/- 0,94). Age, history, and training characteristics were significantly and negatively linked to BMD. After multiple regression, no variable had an independent correlation with BMD. No correlation was found with biomarkers or with training characteristics.Conclusion : Our study shows a worrying proposition of low bone mass in our population of young male and otherwise healthy cyclists. Low energy availability, as the missing point of our study, might be the main causal factor. Great attention should be paid in bone status in elite cyclists of any age.

Quenched disorder-induced chaotic resonance: Optimal stimulus response near the edge of chaos

We study the collective stimulus response in two classical nonlinear dynamical models, the globally coupled bistable oscillators and the excitable FitzHugh-Nagumo neurons, where the coupling strength among the units are randomly distributed with fixed mean and varying variance. We find theoretically and numerically that in both models the ensemble response to a weak periodic stimulus exhibits a bell-shaped amplification manifesting a different type of resonance mechanism, namely, coupling-disorder-induced resonance, as the quenched disorder of coupling increases. Of particular interest is that the optimal collective response emerges near the order-chaos transition point, i.e., at the edge of chaos. As a promising application, we discuss briefly the potential reasonability for exploiting such a type of chaotic resonance to explain the optimal mutual information in the realistic inferior olive. Our results provide explicitly a clue that the disorderly coupled elements may utilize the coupling-disorder-induced chaos to optimize their stimulus response. Published by the American Physical Society 2024

A Systematic Review on Sex Differences in Prepulse Inhibition of Startle

Abstract: Prepulse inhibition of the startle response is defined as the inhibition of the startle reflex to an intense contextual stimulus (named pulse) when a weaker stimulus (named prepulse) precedes it and is considered a measure of sensorimotor gating. Consistent with recent research, it has been observed that this measure might exhibit sex differences in studies of both humans and rodents, although the results in the literature appear to be inconsistent. Therefore, this systematic review aims to analyze the sexual differences observed in human and nonhuman animal studies from a comparative perspective. A comprehensive search was conducted from the inception to the present in the Web of Science, PubMed, and PsycInfo databases. Following the search, 58 studies were included in the review. The average age in human studies ( n = 32) was 31.45 years (range = 4–69), while among nonhuman animal studies ( n = 26), the average age was 75.5 postnatal days (range = 7–360). The results indicated no clear sexual differences in the startle response magnitude. However, consistent sex differences in prepulse inhibition were found, revealing that males exhibited higher levels of sensorimotor gating compared to females in both humans (78.79% of the studies) and nonhuman animal studies (69.23% of the studies). Therefore, the findings corroborate the sex differences of prepulse inhibition and underscore the value of this paradigm in comparative science, emphasizing the importance of considering sex as an independent variable when studying this phenomenon.

Amplification of olfactory transduction currents implements sparse stimulus encoding.

Sensory systems must perform the dual and opposing tasks of being sensitive to weak stimuli while also maintaining information content in dense and variable sensory landscapes. This occurs in the olfactory system, where OSNs are highly sensitive to low concentrations of odors and maintain discriminability in complex odor environments. How olfactory sensory neurons (OSNs) maintain both sensitivity and sparsity is not well understood. Here, we investigated whether the calcium-activated chloride channel, TMEM16B, may support these dual roles in OSNs. We used multiphoton microscopy to image the stimulus-response density of OSNs in the olfactory epithelium. In TMEM16B knockout mice, we found that sensory representations were denser, and the magnitude of OSN responses was increased. Behaviorally, these changes in sensory representations were associated with an increased aversion to the odorant trimethylamine, which switches perceptual valence as its concentration increases, and a decreased efficiency of olfactory-guided navigation. Together, our results indicate that the calcium-activated chloride channel TMEM16B sparsens sensory representations in the peripheral olfactory system and contributes to efficient integrative olfactory-guided behaviors.

Achieving Controllable Thermochromic Fluorescence via Synergistic Intramolecular Charge Transfer and Molecular Packing

Thermochromic fluorescent materials (TFMs) have attracted significant attention due to their unique fluorescent colorimetric response to temperature. However, existing TFMs still suffer from weak stimulus responsiveness, broad temperature response ranges, uncontrollable emission color changes, and low quantum yields. In this study, we address these issues by designing and synthesizing three diketone‐boron complexes with distinct emission wavelengths (NWPU‐(2‐4)). Utilizing a molecular engineering strategy to manipulate intramolecular charge transfer transitions and molecular packing modes, our synthesized complexes exhibit efficient fluorescence emission in both solution and solid states. Moreover, their emission wavelengths are highly sensitive to environmental polarity. By incorporating these compounds into thermosensitive matrices of long‐chain alkanes, we produced TFMs with varied fluorescence emission peak variation ranges. Notably, the TFM based on NWPU‐4, owing to its strong charge transfer transitions and dense J‐aggregate packing configuration, not only exhibits intense fluorescence emission spanning the deep red to near‐infrared spectrum but also displays a remarkable 90 nm broad range of thermochromic properties. Ultimately, it was successfully applied to programmable, thermally controlled, multi‐level information encryption.

Achieving Controllable Thermochromic Fluorescence via Synergistic Intramolecular Charge Transfer and Molecular Packing.

Thermochromic fluorescent materials (TFMs) have attracted significant attention due to their unique fluorescent colorimetric response to temperature. However, existing TFMs still suffer from weak stimulus responsiveness, broad temperature response ranges, uncontrollable emission color changes, and low quantum yields. In this study, we address these issues by designing and synthesizing three diketone-boron complexes with distinct emission wavelengths (NWPU-(2-4)). Utilizing a molecular engineering strategy to manipulate intramolecular charge transfer transitions and molecular packing modes, our synthesized complexes exhibit efficient fluorescence emission in both solution and solid states. Moreover, their emission wavelengths are highly sensitive to environmental polarity. By incorporating these compounds into thermosensitive matrices of long-chain alkanes, we produced TFMs with varied fluorescence emission peak variation ranges. Notably, the TFM based on NWPU-4, owing to its strong charge transfer transitions and dense J-aggregate packing configuration, not only exhibits intense fluorescence emission spanning the deep red to near-infrared spectrum but also displays a remarkable 90 nm broad range of thermochromic properties. Ultimately, it was successfully applied to programmable, thermally controlled, multi-level information encryption.

Herpes simplex reactivation triggers symptom exacerbation in patients with major depressive disorder

BackgroundHerpes Simplex Virus (HSV) infection has been linked to depression, but the underlying mechanism remains largely unknown. We hypothesized that recurring HSV infection could exacerbate depressive symptomatology via activation of the immune response and the kynurenine pathway in patients with Major Depressive Disorder (MDD). Methods32 MDD patients and 17 psychiatrically healthy individuals with a history of HSV recurrence were enrolled into the study. Blood samples were obtained, and psychiatric symptom severity was assessed at three separate visits- asymptomatic, active infection, and follow-up. Plasma levels of tryptophan metabolite levels were measured using ultra-high performance liquid chromatography-mass spectrometry (LC-MS), and inflammation-associated proteins were measured using high sensitivity electrochemiluminescence. ResultsThere was a significant effect of infection recurrence on IFN-γ and sICAM-1 levels, the latter being influenced by MDD diagnosis. This indicates that the effect of infection on sICAM-1 levels differs between control and depressed groups, although post hoc analysis suggests that interaction effect might be subtle. Infection recurrence had a significant effect on the reactivity of psychiatric symptoms. Finally, there was a positive correlation between levels of anti-inflammatory cytokines IL-10 and IL-13 and depression severity in the cohort during infection recurrence. LimitationsRelatively small sample size, limited number of male participants, and the relatively weak inflammatory stimuli studied. ConclusionsMDD patients might react with an exacerbation of symptoms along with elevations of inflammatory markers during HSV recurrence. Further, the association with symptom severity indicates that therapeutic modulation of inflammation may be beneficial in patients with MDD, especially during active infections.

An auditory selective attention brain-computer interface system based on auditory steady-state response

Auditory steady-state response (ASSR) is a brain steady-state response induced by periodic sound signals, which can be used to build an auditory brain-computer interface (BCI), thereby providing a pathway for visually impaired patients to communicate with the outside world. Most of existing ASSR-based BCI studies use linear discriminant classifier (LDA) and spatial coherence to detect ASSRs. Therefore, there is an urgent need for efficient electroencephalogram (EEG) decoding methods to improve the performance of ASSR-based BCI systems. In this study, we elicited ASSRs using sinusoidal amplitude modulated (SAM) tones that simultaneously delivered different modulation frequencies (i.e., 37 Hz for the left channel and 43 Hz for the right channel). Subjects were asked to focus their attention on the auditory stimulation on one side according to the auditory cue. Filter bank common spatial pattern (FBCSP) algorithm was innovatively introduced to detect the ASSRs. Offline results showed that the brain region with strong ASSRs was the central forehead area, and when subjects paid attention to the auditory stimulation at 37 Hz or 43 Hz, the ASSR response of 37 Hz or 43 Hz on the corresponding side would be enhanced compared to the no attention condition. Online results obtained from twelve healthy subjects showed that the mean recognition accuracy of the proposed ASSR-based BCI system achieved a mean accuracy of 82.22 ± 3.11 %. Moreover, the present study further verified that weak auditory stimuli with low stimulus intensity (i.e., 40 dB SPL) could also be used to build ASSR-based BCIs, and achieved an online mean accuracy of 78.89 ± 2.54 %. These results verified that the FBCSP algorithm could be used for detecting ASSRs and the feasibility of the proposed ASSR-based BCI system, providing a great idea for building a high-speed ASSR-based BCI system.

Inhibitory effects of prepulse stimuli on the electrophysiological responses to startle stimuli in the deep layers of the superior colliculus.

Prepulse inhibition (PPI) is a phenomenon where a weak prepulse stimulus inhibits the startle reflex to a subsequent stronger stimulus, which can be induced by various sensory stimulus modalities such as visual, tactile, and auditory stimuli. This study investigates the neural mechanisms underlying auditory PPI by focusing on the deep layers of the superior colliculus (deepSC) and the inferior colliculus (IC) in rats. Nineteen male Sprague-Dawley rats were implanted with electrodes in the left deepSC and the right IC, and electrophysiological recordings were conducted under anesthesia to observe the frequency following responses (FFRs) to startle stimuli with and without prepulse stimuli. Our results showed that in the deepSC, narrowband noise as a prepulse stimulus significantly inhibited the envelope component of the startle response, while the fine structure component remained unaffected. However, this inhibitory effect was not observed in the IC or when the prepulse stimulus was a gap. These findings suggest that the deepSC plays a crucial role in the neural circuitry of PPI, particularly in the modulation of the envelope component of the startle response. The differential effects of narrowband noise and gap as prepulse stimuli also indicate distinct neural pathways for sound-induced PPI and Gap-PPI. Understanding these mechanisms could provide insights into sensory processing and potential therapeutic targets for disorders involving impaired PPI, such as tinnitus.

Antiferromagnetic artificial neuron modeling of the withdrawal reflex.

Replicating neural responses observed in biological systems using artificial neural networks holds significant promise in the fields of medicine and engineering. In this study, we employ ultra-fast artificial neurons based on antiferromagnetic (AFM) spin Hall oscillators to emulate the biological withdrawal reflex responsible for self-preservation against noxious stimuli, such as pain or temperature. As a result of utilizing the dynamics of AFM neurons, we are able to construct an artificial neural network that can mimic the functionality and organization of the biological neural network responsible for this reflex. The unique features of AFM neurons, such as inhibition that stems from an effective AFM inertia, allow for the creation of biologically realistic neural network components, like the interneurons in the spinal cord and antagonist motor neurons. To showcase the effectiveness of AFM neuron modeling, we conduct simulations of various scenarios that define the withdrawal reflex, including responses to both weak and strong sensory stimuli, as well as voluntary suppression of the reflex.

Edge-enhanced super microgenerator based on a two-dimensional Schottky junction

Super microgenerator (SMG) refers to a generator that can efficiently convert extremely weak external stimuli into electrical energy and has a small size, high power density and long lifespan, offer ground-breaking solutions for powering wearable devices, wireless distributed sensors and implanted medical equipment. However, the friction and wear between the interfaces of ordinary microgenerator results in an extremely low lifespan. Here, we present a prototype of SMGs based on a 2D–2D (graphite–MoS2) Schottky contact in the state of structural superlubricity (no wear and nearly zero friction between two contacted solid surfaces). What is even more interesting is when the graphite flake is slid from the bulk to the edge of MoS2, the output current will enhance from 31 to 56 A m−2. Through the I–V curve measurement, we found that the conductive channel across the junction can be activated and further enhanced at the edge of MoS2 compare to bulk, which provide the explanation for the above-mentioned edge enhancement of power generation. Above results provide the design principles of high-performance SMGs based on 2D–2D Schottky junctions.

A Computational Model for the Simulation of Prepulse Inhibition and Its Modulation by Cortical and Subcortical Units.

The sensorimotor gating is a nervous system function that modulates the acoustic startle response (ASR). Prepulse inhibition (PPI) phenomenon is an operational measure of sensorimotor gating, defined as the reduction of ASR when a high intensity sound (pulse) is preceded in milliseconds by a weaker stimulus (prepulse). Brainstem nuclei are associated with the mediation of ASR and PPI, whereas cortical and subcortical regions are associated with their modulation. However, it is still unclear how the modulatory units can influence PPI. In the present work, we developed a computational model of a neural circuit involved in the mediation (brainstem units) and modulation (cortical and subcortical units) of ASR and PPI. The activities of all units were modeled by the leaky-integrator formalism for neural population. The model reproduces basic features of PPI observed in experiments, such as the effects of changes in interstimulus interval, prepulse intensity, and habituation of ASR. The simulation of GABAergic and dopaminergic drugs impaired PPI by their effects over subcortical units activity. The results show that subcortical units constitute a central hub for PPI modulation. The presented computational model offers a valuable tool to investigate the neurobiology associated with disorder-related impairments in PPI.

An ultra thin, bright, and sensitive interactive tactile display based on organic mechanoluminescence for dual‐mode handwriting identification

AbstractVisible light‐based human–machine interactive media is capable of transmitting electrical readouts to machines and providing intuitive feedback to users simultaneously. Currently, many inorganic mechanoluminescent (ML) materials‐based interactive media, typically ZnS‐loaded phosphors (ZLPs), have been successfully demonstrated. However, organic ML materials‐based solutions were rarely exploited despite their huge merits of strong structural modification, abundant luminescence property, low cost, easy preparation, and so on. Here, we propose a novel interactive tactile display (ITD) based on organic ML materials (Cz‐A6‐dye) and triboelectric nanogenerator, with ultra‐brightness (130% enhancement) and ultra‐low threshold pressure (57% reduction) as compared to ZLPs. The proposed ITD achieves the conversion of weak mechanical stimuli into visible light and electrical signals simultaneously, without extra power supplies. Furthermore, the relationship between the luminous performance of organic ML materials and mechanical force is quantified, benefiting from the uniform ML layer prepared. Enabled by convolutional neural networks, the high‐accuracy recognition (97.1%) for handwriting and identity of users is realized at the same time. Thus, the ITD has great potential for intelligent wearable electronics and classified military applications.image

Representing stimulus motion with waves in adaptive neural fields.

Traveling waves of neural activity emerge in cortical networks both spontaneously and in response to stimuli. The spatiotemporal structure of waves can indicate the information they encode and the physiological processes that sustain them. Here, we investigate the stimulus-response relationships of traveling waves emerging in adaptive neural fields as a model of visual motion processing. Neural field equations model the activity of cortical tissue as a continuum excitable medium, and adaptive processes provide negative feedback, generating localized activity patterns. Synaptic connectivity in our model is described by an integral kernel that weakens dynamically due to activity-dependent synaptic depression, leading to marginally stable traveling fronts (with attenuated backs) or pulses of a fixed speed. Our analysis quantifies how weak stimuli shift the relative position of these waves over time, characterized by a wave response function we obtain perturbatively. Persistent and continuously visible stimuli model moving visual objects. Intermittent flashes that hop across visual space can produce the experience of smooth apparent visual motion. Entrainment of waves to both kinds of moving stimuli are well characterized by our theory and numerical simulations, providing a mechanistic description of the perception of visual motion.

Air pollution levels enhance green bond investment: green preference and environmental perception thresholds

Environmental change is a crucial factor influencing green investment, and air pollution affects green assets through green preference. This study analyzes the impact of air pollution levels on the green bond using the threshold model. Since investors have physiological thresholds for perceiving air pollution, green preferences change investor behavior once air pollution reaches a certain threshold. The empirical results confirm that at low air pollution levels, weak physical stimuli are not sufficient to induce strong environmental perceptions, resulting in an insignificant role for green preference. However, when air pollution exceeds the threshold, the effect of air pollution becomes significantly positive due to enhanced environmental perceptions. Additionally, major crisis events (e.g. COVID-19) may weaken the role of green preference by distracting investors, leading to an insignificant impact of air pollution on green bonds after the crisis. These findings help enterprises to achieve green transformation and sustainable development through green debt financing.

Advances in Multifunctional Sensors Based on Triboelectric Nanogenerator – Applications, Triboelectric Materials, and Manufacturing Integration

AbstractWith the rapid development of industry and information technology, rough challenges have been put forward for the traditional sensor technology to meet the increasingly complex and diverse application demands in actual production and daily life, and the widely distributed sensor network also faces complex power supply and maintenance problems. As a new energy conversion technology, triboelectric nanogenerators (TENGs) based on triboelectrification and electrostatic induction effect can respond to the weak mechanical stimuli in the surrounding environment and generate corresponding electrical signals to realize the sensing function without external power supply. In addition, TENGs have the advantages of wide selection of fabrication materials, flexible and diverse fundamental modes, which can be customized for different applications and realize different sensing functions. In recent years, triboelectric sensors based on TENGs have developed rapidly, and researchers have developed variable triboelectric sensors for different application scenarios. In this paper, the developed triboelectric sensos have been classified into different categories, the advanced strategy to prepare advanced triboelectric materials and technology used for manufacturing integration have been introduced. This work summarizes the main applications of triboelectric sensors and put forward the current challenges, so as to provide guidance and instructions for the future development of triboelectric sensors.

A Physical Framework to Study the Effect of Magnetic Fields on the Spike-Time Coding.

A temporal neural code reliant on the pattern of spike times rather than spike rates offers a feasible mechanism for encoding information from weak periodic external stimuli, such as static or extremely low-frequency electromagnetic fields. Our model focuses on the influence of magnetic fields on neurotransmitter dynamics near the neuron membrane. Neurotransmitter binding to specific receptor sites on membrane proteins can regulate biochemical reactions. The duration a neurotransmitter spends in the bonded state serves as a metric for the magnetic field's capacity as a chemical regulator. By initiating a physical analysis of ligand-receptor binding, utilizing the alpha function for synaptic conductance, and employing a modified version of Bell's law, we quantified the impact of magnetic fields on the bond half-life time and, consequently, on postsynaptic spike timing.

Short-latency prepulse inhibition of the trigeminal blink reflex.

Prepulse inhibition (PPI) is a well-established phenomenon wherein a weak sensory stimulus attenuates the startle reflex triggered by a subsequent strong stimulus. Within the circuit, variations in target responses observed for PPI paradigms represent prepulse-induced excitability changes. However, little is known about the mechanism of PPI. Here, we focused on short-latency PPI of the trigeminal blink reflex R1 signal with an oligosynaptic reflex arc through the principal sensory trigeminal nucleus and the facial nucleus. As the facial nucleus is facilitatory to any input, R1 PPI is the phenomenon in the former nucleus. Considering that GABAergic modulation may be involved in PPI, this study investigated whether the PPI mechanism includes GABA-A equivalent inhibition, which peaks at approximately 30 ms in humans. In 12 healthy volunteers, the reflex was elicited by electrical stimulation of the supraorbital nerve, and recorded at the ipsilateral lower eyelid by accelerometer. Stimulus intensity was 1.5 times the R1 threshold for test stimulus and 0.9 times for the prepulse. The prepulse-test interval (PTI) was 5-150 ms. Results showed significant inhibition at 40-and 80-150-ms PTIs but not at 20-, 30-, 50-, 60-, and 70-ms PTIs, yielding two distinct inhibitions of different time scales. This corresponds well to the early and late components of inhibitory post synaptic potentials by GABA-A and GABA-B receptor activation. Thus, the data support the contribution of inhibitory post synaptic potentials elicited by the prepulse to the observed PPI. As inhibitory function-related diseases may impair the different inhibition components to varying degrees, methods deconvoluting each inhibitory component contribution are of clinical importance.