Intermittent Stimuli Research Articles

Exploring the effects of post operative hyperoxic intermittent stimuli on reticulocyte levels in cancer patients: a randomized controlled study

BackgroundAnemia is common among hospitalized critically ill and surgical oncological patients. The rising incidence of cancer and aggressive treatments has increased the demand for blood products, further strained by a dwindling donor pool. The normobaric oxygen paradox (NOP) has emerged as a potential avenue to increase EPO levels. While some studies support its efficacy, research remains limited in clinical settings. This study aims to assess the effectiveness of a NOP protocol in stimulating erythropoiesis, as measured by changes in reticulocyte counts, in cancer patients undergoing abdominal surgeries.MethodsThis is a post hoc analysis of a prospective, single-center, controlled, randomized study. A total of 49 patients undergoing abdominal surgery were analyzed at the Institut Jules Bordet. Adult patients admitted to the intensive care unit (ICU) for at least 24 h were enrolled, excluding those with severe renal insufficiency or who received transfusions during the study period. Participants were randomized into two groups: a normobaric oxygen paradox (OXY) group who received 60% oxygen for 2 h on days 1, 3, and 5 post-surgery and a control (CTR) group who received standard care. Data on baseline characteristics, surgical details, and laboratory parameters were collected. Statistical analysis included descriptive statistics, chi-square tests, t-tests, Mann–Whitney tests, and linear and logistic regression.ResultsThe final analysis included 33 patients (median age 62 [IQR 58–66], 28 (84.8%) males, with no withdrawals or deaths during the study period. No significant differences were observed in baseline surgical characteristics or perioperative outcomes between the two groups. In the OXY group (n = 16), there was a significant rise (p = 0.0237) in the percentage of reticulocyte levels in comparison to the CTR group (n = 17), with median values of 36.1% (IQR 20.3–57.8) versus − 5.3% (IQR − 19.2–57.8), respectively. The increases in hemoglobin and hematocrit levels did not significantly differ between the groups when compared to their baselines’ values.ConclusionsThis study provides preliminary evidence supporting the potential of normobaric oxygen therapy in stimulating erythropoiesis in cancer patients undergoing abdominal surgeries. While the OXY group resulted in increased reticulocyte counts, further research with larger sample sizes and multi-center trials is warranted to confirm these findings.Trial registrationThe study was retrospectively registered under NCT number 06321874 on The 10th of April 2024.

Neural Network Circuits for Bionic Associative Memory and Temporal Order Memory Based on DNA Strand Displacement.

Pavlovian associative memory plays an important role in our daily life and work. The realization of Pavlovian associative memory at the deoxyribonucleic acid (DNA) molecular level will promote the development of biological computing and broaden the application scenarios of neural networks. In this article, bionic associative memory and temporal order memory circuits are constructed by DNA strand displacement (DSD) reactions. First, a temporal logic gate is constructed on the basis of DSD circuit and extended to a three-input temporal logic gate. The output of temporal logic gate is used for the weight species of associative memory. Second, the forgetting module and output module based on the DSD circuit are constructed to realize some functions of associative memory, including associative memory with simultaneous stimulus, associative memory with interstimulus interval effect, and the facilitation by intermittent stimulus. In addition, the coding, storage, and retrieval modules are designed based on the analysis and memory capabilities of temporal logic gate for temporal information. The temporal order memory circuit is constructed, demonstrating the temporal order memory ability of DNA circuit. Finally, the reliability of the circuit is verified through Visual DSD software simulation. Our work provides ideas and inspiration to construct more complex DNA bionic circuits and intelligent circuits by using DSD technology.

A New Multi-mode, High Pressure Portable Transcranial Ultrasound Stimulation System.

Transcranial ultrasound stimulation (TUS) is a promising non-invasive neuromodulation method for brain disorders. Commonly-used TUS systems in research include custom-built and commercial devices. Custom-built devices typically consist of traditional function generator, power amplifier, and ultrasound transducer. Due to cumbersome wiring and absence of dedicated control software, the operation of these devices is inconvenient. Commercial devices often have limited waveform modes and cannot perform ultrasound modulation with complex waveforms. These limitations limit the application of TUS technology by ordinary users. Therefore, we propose a portable TUS system with multiple modes and high acoustic pressure. The proposed portable TUS system utilizes a high-power multi-mode stimulator, and an ultrasound transducer with impedance matching module to achieve multiple modes and high acoustic pressure ultrasound neuromodulation. The stimulator can output four types of waveforms: continuous pulse continuous stimulus (CPCS), intermittent pulse continuous stimulus (IPCS), continuous pulse intermittent stimulus (CPIS), and intermittent pulse intermittent stimulus (IPIS). When using a same transducer, it generates a peak negative pressure that is nearly identical to one produced by a commercial device. And compared to commercial transducer, the peak negative pressure of our transducer is significantly higher, reaching a maximum of 0.95 MPa. In-vitro experiments were conducted using rat hippocampal brain slices. The experimental results demonstrated the effectiveness of the TUS system for neural stimulation. It offers a design method of a portable multi-mode, high pressure TUS system, which is used for complex neural modulation research.

Habituation of auditory responses in young autistic and neurotypical children.

Prior studies suggest that habituation of sensory responses is reduced in autism and that diminished habituation could be related to atypical autistic sensory experiences, for example, by causing brain responses to aversive stimuli to remain strong over time instead of being suppressed. While many prior studies exploring habituation in autism have repeatedly presented identical stimuli, other studies suggest group differences can still be observed in habituation to intermittent stimuli. The present study explored habituation of electrophysiological responses to auditory complex tones of varying intensities (50-80 dB SPL), presented passively in an interleaved manner, in a well-characterized sample of 127 autistic (MDQ = 65.41, SD = 20.54) and 79 typically developing (MDQ = 106.02, SD = 11.50) children between 2 and 5 years old. Habituation was quantified as changes in the amplitudes of single-trial responses to tones of each intensity over the course of the experiment. Habituation of the auditory N2 response was substantially reduced in autistic participants as compared to typically developing controls, although diagnostic groups did not clearly differ in habituation of the P1 response. Interestingly, the P1 habituated less to loud 80 dB sounds than softer sounds, whereas the N2 habituated less to soft 50 dB sounds than louder sounds. No associations were found between electrophysiological habituation and cognitive ability or participants' caregiver-reported sound tolerance (Sensory Profile Hyperacusis Index). The results present study results extend prior research suggesting habituation of certain sensory responses is reduced in autism; however, they also suggest that habituation differences observed using this study's paradigm might not be a primary driver of autistic participants' real-world sound intolerance.

Using Signal-to-Noise Ratio to Explore The Cognitive Cost of The Detection Response Task

The Detection Response Task (DRT) is a standardized measure of cognitive load requiring manual responses to intermittent stimuli. Given its simplicity, it is hypothesized that its completion will not interfere with the primary task. However, recent studies challenge this assumption showing a definite cost of DRT performance. In this study we adopt signal-to-noise ratio (SNR), a measure commonly used in communication engineering: 1) to explore the cognitive cost of DRT 2) to compare the sensitivity of DRT performance and pupil size in measuring cognitive load. SNR was calculated using the data from a study wherein DRT performance and pupil size were recorded while participants completed increasingly difficult mental tasks. We conclude that DRT completion interfered with the overall cognitive task demand and showed pupil size’s greater sensitivity to changes in cognitive load. Though exploratory, our study advances using SNR as a powerful tool for data integration in HF/E research.

Growth regulation by air stream-based mechanical stimulation in tomato (Solanum lycopersicum L.) – Part I: optimization of application frequency and intensity

Stem elongation control is a fundamental requirement for the production of high-quality seedlings in terms of plant compactness and stability. It is known that stem elongation of seedlings can be inhibited by mechanical stimulation. In this study, a custom-built air stream applicator was used to apply intermittent stimuli to tomato (Solanum lycopersicum cv. ‘Romello’). Tomato plants were cultivated under greenhouse conditions for 21 days and then exposed to intermittent air stimuli at different air stream application frequencies (8, 24, 40, 56, 72 and 80 d−1) and different air stream velocities (0.7 – 6.0 m s−1) for 14 days. Tomato plants responded with an inhibition of stem elongation of approximately 31% compared to the untreated control, without a systematic dose-response relationship related to application frequency. In contrast, stem elongation inhibition was significantly affected by air velocity, with a sigmoid dose-response relationship with negligible effects up to 2.0 m s−1, followed by a steep increase in the reduction effect up to 4.7 m s−1 and a fading of the effect at 36 % reduction for air velocities beyond that. Dry mass of leaves, stems, and petioles was reduced by approximately 10%, 41%, and 19%, respectively, after 14 days of treatment at a gradually increasing air velocity from 3.5 m s−1 at day 0 to 6.1 m s−1 at day 14 and an application frequency of 8 d−1. Root dry mass was less affected by the air stream application, but showed a slight tendency to decrease compared to control plants.

Spontaneous State Detection Using Time-Frequency and Time-Domain Features Extracted From Stereo-Electroencephalography Traces.

As a minimally invasive recording technique, stereo-electroencephalography (SEEG) measures intracranial signals directly by inserting depth electrodes shafts into the human brain, and thus can capture neural activities in both cortical layers and subcortical structures. Despite gradually increasing SEEG-based brain-computer interface (BCI) studies, the features utilized were usually confined to the amplitude of the event-related potential (ERP) or band power, and the decoding capabilities of other time-frequency and time-domain features have not been demonstrated for SEEG recordings yet. In this study, we aimed to verify the validity of time-domain and time-frequency features of SEEG, where classification performances served as evaluating indicators. To do this, using SEEG signals under intermittent auditory stimuli, we extracted features including the average amplitude, root mean square, slope of linear regression, and line-length from the ERP trace and three traces of band power activities (high-gamma, beta, and alpha). These features were used to detect the active state (including activations to two types of names) against the idle state. Results suggested that valid time-domain and time-frequency features distributed across multiple regions, including the temporal lobe, parietal lobe, and deeper structures such as the insula. Among all feature types, the average amplitude, root mean square, and line-length extracted from high-gamma (60–140 Hz) power and the line-length extracted from ERP were the most informative. Using a hidden Markov model (HMM), we could precisely detect the onset and the end of the active state with a sensitivity of 95.7 ± 1.3% and a precision of 91.7 ± 1.6%. The valid features derived from high-gamma power and ERP in this work provided new insights into the feature selection procedure for further SEEG-based BCI applications.

Acute imagery resistance exercise improves subsequent muscle power performance in teenage futsal athletes

Background: Futsal is one of the most popular sport in Brazil with millions of players worldwide. It is characterized by intermittent stimuli of high intensity anaerobic actions. Recently, studies have shown that imagery resistance training (IRT), like conventional strength training, can increase muscle strength, making it reasonable to think that this effect can also be transferred to muscle power. Purposes: we aimed to verify the acute responses of IRT on muscle power in teenage Futsal players. Methods: fifteen Futsal athletes were enrolled and underwent three visits to the laboratory: 1) familiarization with the resistance exercise they would undergo; 2) one them for vertical jump test after the IRT session and the other one for control session, without any intervention before vertical jump test. Sessions 2 and 3 being applied in random order. Results: the results indicate that acute IRT improved muscle performance, since it produced higher power output [3134.5 Watts (2744 - 3796.3)] than control session [2952.4 Watts (2637.55 - 3433.45)] (Z=3.4078; p=0.0007). In addition, all participants in IRT group showed some improvement after the IRT session. Conclusions: a single imagery resistance exercise session can increase acute muscle power output in teenage Futsal athletes.

Pheromone binding protein is involved in temporal olfactory resolution in the silkmoth

SummaryMale moths utilize spatio-temporal female sex pheromone information to orient toward conspecific females. Pheromones are distributed as discontinuous plumes owing to air turbulence; thus, efficient tracking of intermittent stimuli is expected to require a high temporal resolution. Here, using pheromone binding protein (BmPBP1)-knockout silkmoths, we showed that a loss of functional PBP lowered the temporal sensory resolution of male antennae. This altered temporal resolution resulted in significantly reduced straight walking and longer turning behavior, which respectively occurred when males detected and lost contact with pheromones, indicating that temporal resolution was also lowered at the behavioral level. BmPBP1-knockout males required significantly longer time than wild-type males in locating pheromone sources and female moths. Our results suggest that BmPBP1 plays a critical role in determining olfactory response kinetics. Accordingly, high temporal olfactory and behavioral resolutions, as shaped by PBP, are essential for tracking pheromone plumes and locating females efficiently.

Hemodynamic response varies across tactile stimuli with different temporal structures.

Tactile stimuli can be distinguished based on their temporal features (e.g., duration, local frequency, and number of pulses), which are fundamental for vibrotactile frequency perception. Characterizing how the hemodynamic response changes in shape across experimental conditions is important for designing and interpreting fMRI studies on tactile information processing. In this study, we focused on periodic tactile stimuli with different temporal structures and explored the hemodynamic response function (HRF) induced by these stimuli. We found that HRFs were stimulus‐dependent in tactile‐related brain areas. Continuous stimuli induced a greater area of activation and a stronger and narrower hemodynamic response than intermittent stimuli with the same duration. The magnitude of the HRF increased with increasing stimulus duration. By normalizing the characteristics into topographic matrix, nonlinearity was obvious. These results suggested that stimulation patterns and duration within a cycle may be key characters for distinguishing different stimuli. We conclude that different temporal structures of tactile stimuli induced different HRFs, which are essential for vibrotactile perception and should be considered in fMRI experimental designs and analyses.

The effect of stimulus contrast on the harmonic components of steady state visual evoked potentials

AbstractPurposeSteady state visual evoked potentials (ssVEP) are widely used for objective functional diagnostics. Due to stimulation with intermittent stimuli, the evoked response contains frequency components related to the stimulation frequency and its harmonics. In general, the evoked amplitude at stimulation frequency is used for functional diagnostics. However, clinicals trails also reported main components at harmonic frequencies. The origin of the harmonic frequency components is not fully understood. This work aims to analyze the influence of the stimulation contrast on harmonic components of ssVEP.MethodsWe studied 10 healthy subjects (mean age 27.2 ± 5.8 years) using checkerboard stimuli (d = 7.2°) with a check size of 0.35°. Stimuli were presented in pattern‐reversal mode (7.5 changes per second) for 5 contrast levels (98%, 50%, 25%, 12.5%, 10%) at mean luminance of 50 cd/m2 and 20 cd/m2 in a random order. The active electrode was placed at Oz, reference electrode at FCz and ground electrode at FPz. The stimulations were performed monocularly in a dimmed room. The recorded ssVEP were transformed using Fourier Analysis. The normalized ratio of the amplitudes at stimulation frequency (7.5 Hz) and first harmonic (15 Hz) were calculated. For statistical analysis Wilcoxon test for paired samples were used.ResultsIn our investigation, all 10 subjects exhibited the main component at stimulation frequency (7.5 Hz). The normalized ratio of the amplitudes showed no significant differences between the 5 contrast levels for the mean luminance of 50 cd/m2 and 20 cd/m2.ConclusionThe presented work revealed, that main components at harmonic frequencies are not dependent on the stimulation contrast. The stimulation contrast has no significant effect on the harmonic responses of ssVEP.

The mechanical loading and muscle activation of four common exercises used in osteoporosis prevention for early postmenopausal women

High impact exercise can reduce postmenopausal bone loss, however stimulus frequency (loading cycles per second) can affect osteogenesis. We aimed to examine the effect of stimulus frequency on the mechanical loading of four common osteoporosis prevention exercises, measuring body acceleration and muscle activation with accelerometry and electromyography (EMG), respectively. Fourteen early postmenopausal women completed randomised countermovement jumps (CMJ), box-drops (BD), heel-drops (HD) and stamp (STP) exercises for continuous and intermittent stimulus frequencies. Sacrum accelerometry and surface electromyography (EMG) of four muscles were recorded. CMJ (mean ± SD: 10.7 ± 4.8 g & 10.0 ± 5.0 g), BD (9.6 ± 4.1 g & 9.5 ± 4.0 g) and HD (7.3 ± 3.8 g & 8.6 ± 4.4 g) conditions generated greater peak acceleration than STP (3.5 ± 1.4 g & 3.6 ± 1.7 g) across continuous and intermittent trials. CMJ and BD generated greater acceleration gradients than STP across continuous and intermittent trials. CMJ generated greater rectus femoris EMG than all other exercises, CMJ and BD generated greater semitendinosus and tibialis anterior EMG than HD across continuous and intermittent trials. CMJ and BD provide greater peak acceleration than STP and remain similar during different stimulus frequencies. CMJ, BD and HD may exceed STP in maintaining postmenopausal bone health.

Vertical Jump Is Strongly Associated to Running-Based Anaerobic Sprint Test in Teenage Futsal Male Athletes.

As one of the most popular sport modalities in Brazil, and with an exponential growth in Europe, futsal is characterized by intermittent stimulus of anaerobic high intensity sprints. The running-based anaerobic sprint test (RAST) is one of the most common tests to assess anaerobic power in futsal athletes, however, it presents both time and physical challenges. Therefore, we aimed to correlate RAST with a simpler test, the vertical jump (VJ), in teenage male futsal athletes; Methods: Thirteen volunteers were enrolled and underwent two visits to the laboratory, one for the VJ and the other for the RAST in a randomized order; Results: The association test indicates a strong and significant correlation between VJ and RAST. We conclude that VJ can be used as an alternative to RAST in teenage male futsal athletes.

The relation of discrete stimuli can be integrated despite the failure of conscious identification

ABSTRACTThe integration of the sameness or difference of two unconscious stimuli occurs and affects behaviour without subjective visual consciousness. Yet, intermittent stimulus awareness or a process simpler than integration could also account for these results. In a masked go/no-go task, participants provided or withheld a response based on the same/different relation of two stimuli. Post-trial performance on a discrimination task was used to classify invisible stimuli, providing an objective criterion of awareness. Stimulus pairs with a No-go-associated relation showed reduced and slower responding even when those stimuli were incorrectly discriminated and presumably unconscious. Due to the large set of stimuli, this effect is unlikely to be due to response mapping or action triggers. The integration of the relation of discrete stimuli is a cognitive function that is not dependent upon visual awareness, in the form of conscious identification, to occur.

Effect of Intermittent versus Continuous Light Exposure on Pupillary Light Response, As Evaluated by Pupillometry.

Continuous and intermittent stimuli with green light affect the pupillary light response (PLR) differently. Since the majority of pupillometric studies use blue and red lights, we investigated the effect of continuous and intermittent stimulations on the PLR using red and blue lights. Seventeen healthy subjects underwent continuous- and intermittent light stimuli, using red (643 nm) and blue light (463 nm). To avoid the influence of pupil size on the amount of light entering the eye, the procedures were repeated with the stimulus-eye in dilated condition. The maximal pupillary constriction and the early redilation phase of post-illumination pupillary response (PIPREarly) represented the mixed response of melanopsin and rod-cone photoreceptors. The late redilation phase of PIPR (PIPRLate) was the marker of melanopsin-containing retinal ganglion cells. Intermittent stimuli with blue light elicited significantly larger maximal contraction during dilated condition (P = 0.001), and larger sustained pupillary contraction under dilated as well as undilated condition (P < 0.001) compared to continuous light exposure. Except the PIPREarly during undilated condition, none of the PIPR metrics were significantly different between intermittent and continuous blue light stimuli. Intermittent red light stimuli elicited also a more sustained pupillary contraction regardless of mydriatic instillation (P ≤ 0.02). In addition, intermittent red light exposure resulted in a slightly larger PIPREarly under undilated condition (P = 0.02) and a slightly larger PIPRLate under dilated condition (P = 0.049). Except the PIPRLate to continuous red light stimulus, all PIPR parameters were larger when the light was presented after induction of unilateral mydriasis. PLR parameters during and after light exposures depend on both the light stimulation mode and the entrance pupillary size.

Cardiovascular autonomic effects of vagus nerve stimulation.

The vagus nerve is responsible for the parasympathetic innervation of the major thoracic and abdominal organs. It also carries sensory afferent fibres from these viscera and reaches different brain structures. These connections have proven useful in the treatment of different diseases. Afferent stimulation of the left vagus nerve is used to treat epilepsy and major depression, and stimulation of the right vagus nerve is being tried for the treatment of heart failure. The device used for the therapy delivers intermittent stimuli. It is indicated worldwide for the treatment of drug-resistant epilepsy in patients who are not appropriate candidates for respective surgery. It has also received approval for the treatment of major depression, obesity and episodic cluster headache by the Food and Drug Administration. Randomised controlled trials and prospective studies have confirmed the efficacy and safety of this therapy in epilepsy. Nevertheless, sporadic cases of ventricular asystole have been reported. To evaluate the effect of vagus nerve stimulation therapy on the autonomic nervous system, different studies that assess heart function and blood pressure changes have been conducted, although the methods employed were not homogeneous. These studies have found subtle or no significant changes in heart rate variability and blood pressure in epileptic patients. Moreover, this therapy may reduce the risk of one of the most lethal conditions in epilepsy-sudden unexpected death.

From road distraction to safe driving: Evaluating the effects of boredom and gamification on driving behaviour, physiological arousal, and subjective experience

Boredom and low levels of task engagement while driving can pose road safety risks, e.g., inattention during low traffic, routine trips, or semi-automated driving. Digital technology interventions that increase task engagement, e.g., through performance feedback, increased challenge, and incentives (often referred to as ‘gamification’), could therefore offer safety benefits. To explore the impact of such interventions, we conducted experiments in a high-fidelity driving simulator with thirty-two participants. In two counterbalanced conditions (control and intervention), we compared driving behaviour, physiological arousal, and subjective experience. Results indicate that the gamified boredom intervention reduced unsafe coping mechanisms such as speeding while promoting anticipatory driving. We can further infer that the intervention not only increased one's attention and arousal during the intermittent gamification challenges, but that these intermittent stimuli may also help sustain one's attention and arousal in between challenges and throughout a drive. At the same time, the gamified condition led to slower hazard reactions and short off-road glances. Our contributions deepen our understanding of driver boredom and pave the way for engaging interventions for safety critical tasks.

Lesions to right posterior parietal cortex impair visual depth perception from disparity but not motion cues.

The posterior parietal cortex (PPC) is understood to be active when observers perceive three-dimensional (3D) structure. However, it is not clear how central this activity is in the construction of 3D spatial representations. Here, we examine whether PPC is essential for two aspects of visual depth perception by testing patients with lesions affecting this region. First, we measured subjects' ability to discriminate depth structure in various 3D surfaces and objects using binocular disparity. Patients with lesions to right PPC (N = 3) exhibited marked perceptual deficits on these tasks, whereas those with left hemisphere lesions (N = 2) were able to reliably discriminate depth as accurately as control subjects. Second, we presented an ambiguous 3D stimulus defined by structure from motion to determine whether PPC lesions influence the rate of bistable perceptual alternations. Patients' percept durations for the 3D stimulus were generally within a normal range, although the two patients with bilateral PPC lesions showed the fastest perceptual alternation rates in our sample. Intermittent stimulus presentation reduced the reversal rate similarly across subjects. Together, the results suggest that PPC plays a causal role in both inferring and maintaining the perception of 3D structure with stereopsis supported primarily by the right hemisphere, but do not lend support to the view that PPC is a critical contributor to bistable perceptual alternations.This article is part of the themed issue ‘Vision in our three-dimensional world’.

Early life sensory ability-ventilatory responses of thornback ray embryos (Raja clavata) to predator-type electric fields.

Predator avoidance is fundamental for survival and it can be particularly challenging for prey animals if physical movement away from a predatory threat is restricted. Many sharks and rays begin life within an egg capsule that is attached to the sea bed. The vulnerability of this sedentary life stage is exacerbated in skates (Rajidae) as the compulsory ventilatory activity of embryos makes them conspicuous to potential predators. Embryos can reduce this risk by mediating ventilatory activity if they detect the presence of a predator using an acute electrosense. To determine how early in embryonic life predator elicited behavioral responses can occur, the reactions of three different age groups (1/3 developed, 2/3 developed, and near hatching) of embryonic thornback rays Raja clavata were tested using predator-type electric field stimuli. Egg capsules were exposed to continuous or intermittent stimuli in order to assess varying predator-type encounter scenarios on the ventilatory behavior of different developmental stages. All embryos reacted with a "freeze response" following initial electric field (E-field) exposure, ceasing ventilatory behavior in response to predator presence, demonstrating electroreceptive functionality for the first time at the earliest possible stage in ontogeny. This ability coincided with the onset of egg ventilatory behavior and may represent an effective means to enhance survival. A continuous application of stimuli over time revealed that embryos can adapt their behavior and resume normal activity, whereas when presented intermittently, the E-field resulted in a significant reduction in overall ventilatory activity across all ages. Recovery from stimuli was significantly quicker in older embryos, potentially indicative of the trade-off between avoiding predation and adequate respiration. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 721-729, 2016.

Odorant concentration differentiator for intermittent olfactory signals.

Animals need to discriminate differences in spatiotemporally distributed sensory signals in terms of quality as well as quantity for generating adaptive behavior. Olfactory signals characterized by odor identity and concentration are intermittently distributed in the environment. From these intervals of stimulation, animals process odorant concentration to localize partners or food sources. Although concentration-response characteristics in olfactory neurons have traditionally been investigated using single stimulus pulses, their behavior under intermittent stimulus regimens remains largely elusive. Using the silkmoth (Bombyx mori) pheromone processing system, a simple and behaviorally well-defined model for olfaction, we investigated the neuronal representation of odorant concentration upon intermittent stimulation in the naturally occurring range. To the first stimulus in a series, the responses of antennal lobe (AL) projection neurons (PNs) showed a concentration dependence as previously shown in many olfactory systems. However, PN response amplitudes dynamically changed upon exposure to intermittent stimuli of the same odorant concentration and settled to a constant, largely concentration-independent level. As a result, PN responses emphasized odorant concentration changes rather than encoding absolute concentration in pulse trains of stimuli. Olfactory receptor neurons did not contribute to this response transformation which was due to long-lasting inhibition affecting PNs in the AL. Simulations confirmed that inhibition also provides advantages when stimuli have naturalistic properties. The primary olfactory center thus functions as an odorant concentration differentiator to efficiently detect concentration changes, thereby improving odorant source orientation over a wide concentration range.