Multiple Spikes Research Articles

Rapid Increase of a SAR-CoV-2 (COVID-19) Variant with Multiple Spike Protein Mutations

Rapid Increase of a SAR-CoV-2 (COVID-19) Variant with Multiple Spike Protein Mutations

Mathematical analysis of multiple spike time series synchronized in phase with collective theta wave using neural cell model

AbstractInformation processing in the brain is performed by the interactions of numerous number of neurons. However, much remains unknown about complex behaviors of a network composed of numerous number of neurons. Especially, in what case cross frequency coupling emerges and how it alters timings of individual firing are open questions. Therefore, in order to quantitatively evaluate the dynamics of the nervous group, we reproduced phenomena such as cross frequency coupling observed in the brain on a mathematical model and analyzed. The analyses of Fokker‐Planck equation provide the region of gamma/theta oscillations as well as their cross‐frequency couplings. In addition, we demonstrated that the populational oscillation synchronizes sequences of spike trains, which is supposed to be a possible mechanism of memory coding in hippocampus by theta‐gamma neural code.

Titanium isotope fractionation in solar system materials

New methods to determine the titanium (Ti) mass-dependent isotope fractionation of solar system materials to high precision were developed by combining internally normalised Ti isotope data with double-spike analyses utilising a 47Ti-49Ti double spike. The procedure includes a three-stage ion-exchange separation procedure to isolate Ti from the sample matrix that provides high-purity Ti fractions that are necessary for high-precision Ti isotope analyses. Analyses of sample aliquots that were spiked before and after the ion-exchange separation procedure demonstrate that Ti isotope fractionation can be induced by the separation procedure. This outcome requires the addition of the double spike before the ion exchange separation procedure in order to accurately determine the natural mass-dependent Ti isotope fractionation of samples. Multiple double spike analyses of an Alfa Aesar Ti standard performed over eight months yielded a reproducibility (2σ standard deviation) of 0.033‰ for δ49/47Ti (differences in 49Ti/47Ti relative to the OL-Ti standard). Terrestrial sample analyses display a 2σ reproducibility of 0.018 to 0.031‰ for δ49/47Ti. Titanium isotope results for three terrestrial USGS magmatic reference samples (AGV-2, BHVO-2 and BCR-2) agree well with literature data and therefore demonstrate the accuracy and precision of the presented methodologies. Achondritic meteorites display an overall range of 0.75‰ for δ49/47Ti. The ungrouped achondrite NWA 7325 has a more positive composition by 0.64‰ for δ49/47Ti compared to all other investigated samples likely reflecting Ti isotope fractionation induced by magmatic differentiation associated with highly reducing conditions and potentially associated with oxide and plagioclase formation. In contrast, eucrites with δ49/47Ti of -0.020 ± 0.070 and -0.003 ± 0.033 and the first mass-dependent Ti isotope data for an acapulcoite (Dhofar 125; δ49/47Ti = 0.094 ± 0.033) show only limited magmatic Ti isotope fractionation. Chondrites also display a relatively restricted range of 0.085‰ for δ49/47Ti, including one calcium‑aluminum rich inclusion (CAI) from Allende and the first mass-dependent Ti isotope data for two Rumuruti chondrites (NWA 753 and NWA 755). Furthermore, the mass-dependent Ti isotope composition of chondrites overlaps with that of eucrites and the acapulcoite Dhofar 125 indicating that nebular processes induce only limited Ti isotope fractionation. Additionally, the Ti isotope data indicate that thermal metamorphism also produced marginal Ti isotope fractionation at the bulk sample scale for chondrites. Small mass-dependent Ti isotope variations between different bulk meteorite samples are also evident, which might reflect sample heterogeneity. Importantly, the mass-dependent Ti isotope composition of the Earth and Moon overlap with the composition of the investigated chondrites, eucrites and acapulcoites within the 2 standard deviation uncertainties.

Atypical benzodiazepine misuse and withdrawal in patient with epilepsy: a case report

BackgroundBenzodiazepines (BDZ) are a class of psychoactive drugs that have been widely used for the treatment of many medical conditions. In this paper, a case of an atypical pattern of diazepam dependence in a patient with epilepsy is presented. The article may be an interesting proposition for rational management in the treatment of benzodiazepine dependence in a patient with non-withdrawal and withdrawal seizures. Detoxification is used then to optimize neurological treatment.Case presentationA 52-year-old Caucasian male, diagnosed with epilepsy with partial complex, and rarely tonic-clonic seizures and benzodiazepine (diazepam) misuse, was admitted to a detoxification unit specialized to treat substance dependence. This patient presented an atypical schedule of substance misuse with a weekly dose of 40 to 45 mg of diazepam, taken once a week, every Saturday. The patient reported having a group of symptoms that usually preceded generalized seizures that were described as the “aura” manifesting as confusion, derealisation, anxiety, and difficulties in speaking. First Saturday after admission to the hospital, the first aura experience was reported, while diazepam level in serum was higher than usual, which was supporting also strong psychological background for withdrawal. On weekend days, 3 weeks after admission, when the patient was receiving 3 mg of diazepam daily, he developed a severe “aura.” The EEG showed no seizure activity. Two weeks later (again Friday to Saturday), the patient reported the occurrence of aura, the EEG recording showed paroxysmal discharges, generalized multiple spikes associated with slow waves, lasting about 30 s, accompanied by eyelid myoclonia and disturbed consciousness. A week later another aura developed that resolved spontaneously without a seizure. Twelve days later, diazepam was completely removed; the elimination of serum benzodiazepines took place. The patient did not report aura until the end of the stay and he was dismissed 5 weeks later.ConclusionsThe differential diagnosis of an aura can be challenging. Carefully proceed serum monitored elimination of benzodiazepines in epileptic patients may serve in safety benefits and helps to achieve detoxification goals. Hence, it is important to prevent, recognize, and treat benzodiazepine dependence in every patient and may improve epilepsy treatment outcome.

Synergistic effects of potassium channel blockers and pyrethroids: mosquitocidal activity and neuronal mode of action†.

The purpose of this research was to explore the possibility of co-applying pyrethroids (agonists of voltage-sensitive sodium channels) with potassium channel blockers in order to potentiate the neurological effects of pyrethroids on Anopheles gambiae. We hypothesized that the toxicity of pyrethroids caused by persistent sodium currents would be augmented by blockage of outward potassium current flow, which normally repolarizes the membrane potential during a nerve membrane action potential. Topical treatments with LD10 s (10% mortality doses) of synergists were given with pyrethroids. 2S-65465 (2S) showed the best synergism of permethrin (8.6-fold) and deltamethrin (7.2-fold), whereas piperonyl butoxide and 4-aminopyridine only showed 2.2- to 3.4-fold synergism with these pyrethroids. In electrophysiological recordings of Periplaneta americana giant axons, 2S (10μm) and 4-AP (30 μm) caused multiple spikes after a single stimulation. Permethrin at 10μm showed significant summating depolarization (4.5 ± 1.1mV) after a train of ten stimuli were applied at 5Hz, and deltamethrin at 0.03 μm showed significant membrane depolarization of 2.9± 0.4mV without stimuli. 2S at 0.3μm and 4-AP at 1-3μm significantly synergized the effects of 3μm permethrin and 0.01 μm deltamethrin. Co-application of potassium channel blockers 2S and 4-AP with pyrethroids can synergize the mosquitocidal activities on An.gambiae, and these activities are correlated with synergistic effects at the level of the nerve membrane. If deployed in the field, this approach can potentially reduce the amount of chemicals needed for effective control of mosquitoes. © 2020 Society of Chemical Industry.

Mathematical Analysis of Multiple Spike Time Series Synchronized in Phase with Collective Theta Wave Using Neural Cell Model

Mathematical Analysis of Multiple Spike Time Series Synchronized in Phase with Collective Theta Wave Using Neural Cell Model

Synchrony of Spontaneous Burst Firing between Retinal Ganglion Cells Across Species.

Neurons communicate with other neurons in response to environmental changes. Their goal is to transmit information to their targets reliably. A burst, which consists of multiple spikes within a short time interval, plays an essential role in enhancing the reliability of information transmission through synapses. In the visual system, retinal ganglion cells (RGCs), the output neurons of the retina, show bursting activity and transmit retinal information to the lateral geniculate neuron of the thalamus. In this study, to extend our interest to the population level, the burstings of multiple RGCs were simultaneously recorded using a multi-channel recording system. As the first step in network analysis, we focused on investigating the pairwise burst correlation between two RGCs. Furthermore, to assess if the population bursting is preserved across species, we compared the synchronized bursting of RGCs between marmoset monkey (callithrix jacchus), one species of the new world monkeys and mouse (C57BL/6J strain). First, monkey RGCs showed a larger number of spikes within a burst, while the inter-spike interval, burst duration, and inter-burst interval were smaller compared with mouse RGCs. Monkey RGCs showed a strong burst synchronization between RGCs, whereas mouse RGCs showed no correlated burst firing. Monkey RGC pairs showed significantly higher burst synchrony and mutual information than mouse RGC pairs did. Comprehensively, through this study, we emphasize that two species have a different bursting activity of RGCs and different burst synchronization suggesting two species have distinctive retinal processing.

Accelerating genomics-based surveillance for COVID-19 response in Africa

Accelerating genomics-based surveillance for COVID-19 response in Africa

In situ structural analysis of SARS-CoV-2 spike reveals flexibility mediated by three hinges.

The spike protein (S) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is required for cell entry and is the primary focus for vaccine development. In this study, we combined cryo-electron tomography, subtomogram averaging, and molecular dynamics simulations to structurally analyze S in situ. Compared with the recombinant S, the viral S was more heavily glycosylated and occurred mostly in the closed prefusion conformation. We show that the stalk domain of S contains three hinges, giving the head unexpected orientational freedom. We propose that the hinges allow S to scan the host cell surface, shielded from antibodies by an extensive glycan coat. The structure of native S contributes to our understanding of SARS-CoV-2 infection and potentially to the development of safe vaccines.

Abstract 6630: Synergistic immuno photothermal nanotherapy (SYMPHONY) for combination cancer therapy

Abstract Checkpoint inhibitor immunotherapy has been a revolutionary milestone in cancer treatment because it can counter the tumor immunosuppressive environment to improve patients' overall survival and even result in a durable complete response. However, only a fraction of patients benefit from checkpoint inhibitor immunotherapy. Improving the response rate and maximizing efficacy for immunotherapy are still unmet needs of great clinical significance. We have developed a novel combination cancer therapy referred to as Synergistic Immuno Photothermal Nanotherapy (SYMPHONY) by integrating plasmonic gold nanostars (GNS)-mediated photothermal therapy with anti-PD-L1 checkpoint inhibitor immunotherapy to improve the therapeutic efficacy of cancer treatment. GNS nanoparticles are superior photon-to-heat conversion transducers for photothermal therapy because they have tip-enhanced plasmonics from multiple sharp spikes and tunable plasmonic absorption in the near-infrared tissue optical window. Our in vivo experimental results with bladder cancer and brain cancer murine animal models have demonstrated that photothermal therapy with GNS in combination with anti-PD-L1 checkpoint inhibitor immunotherapy not only effectively ablates primary tumor with laser irradiation but also stimulates the immune response to treat distant tumors without laser irradiation. Furthermore, a rechallenge study performed three months later using cancer cells injected into long-term survivors demonstrates that SYMPHONY therapy can generate a long-term memorized immune response and prevent cancer recurrences in cured mice. The SYMPHONY combination therapy results in synergistic treatment surpassing what either single treatment can achieve, and shows the great promise for future translational medicine studies to treat aggressive metastatic cancer diseases. Citation Format: Yang Liu, Paolo Maccarini, Gregory M. Palmer, Brant A. Inman, Peter E. Fecci, Tuan Vo-Dinh. Synergistic immuno photothermal nanotherapy (SYMPHONY) for combination cancer therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6630.

Prognostic Factors of Patients with Postinfantile Epilepsy and Multiple Independent Spike Foci on Electroencephalography

Purpose Multiple independent spike foci (MISF) have been reported to be associated with hypsarrhythmia and slow spikes and waves. However, some patients with MISF demonstrate a good prognosis, such as benign focal epilepsy. This study aimed to elucidate the prognosis of epileptic children with MISF and to analyze the prognostic factors. Methods The subjects were 115 epileptic children aged 1 to 18 years who visited Pusan National University Children’s Hospital between November 2008 and July 2016 and in whom MISF were noted on electroencephalography. We excluded patients with infantile spasms, congenital metabolic diseases, neurodegenerative diseases, or post-encephalitic epilepsy. We retrospectively reviewed participants’ clinical information. Seizure control was defined as no seizures over 6 months at the last visit. Prognostic factors were analyzed in the seizure control (group A; 84 [73%]) and no seizure control (group B; 31 [27%]) groups. Results Generalized seizure (P=0.033), intellectual disability (P<0.001), cerebral palsy (P=0.046), and abnormal background activity and electrodecrements on electroencephalography (P<0.001) were significantly more common in group B. No clinically significant abnormalities were noted on magnetic resonance imaging of the brain. The MISF improved on follow-up electroencephalography in 58 (71.6%) patients in group A versus 10 (35.7%) in group B (P=0.002). Conclusion Despite MISF on electroencephalography, two-thirds of patients had a benign clinical course, particularly those with post-infantile epilepsy and no infantile spasms. The prognostic factors of poor outcomes were generalized seizures, intellectual disability, and abnormal background activity on electroencephalography. Keywords: Child; Electroencephalography; Epilepsy; Prognosis

A multiple inflated negative binomial hurdle regression model: analysis of the Italians\u2019 tourism behaviour during the Great Recession

We analyse tourism behaviour of Italian residents in the period covering the 2008 Great Recession. Using the Trips of Italian Residents in Italy and Abroad quarterly survey, carried out by the Italian National Institute of Statistics, we investigate whether and how the economic recession has affected the total number of overnight stays. The response variable is the result of a two-stage decision process: first we choose to take a holiday, then for how long. Moreover, since the number of overnight stays is typically concentrated on specific lengths (week-end, week, fortnight) we observe multiple peculiar spikes in its distribution. To take into account these two distinctive characteristics, we generalise the usual hurdle regression model by specifying a multiple inflated truncated negative binomial distribution for the positive responses. Results show that the economic recession impacted negatively on both components of the decision process and that, by controlling for the inflated nature of the response variable’s distribution, the proposed formulation provides a better representation of the Italians’ tourism behaviour in comparison with non-inflated hurdle models. Given this, we believe that our model can be a useful tool for policy makers who are trying to forecast the effects of new targeted policies to support tourism economy.

Interactions between calmodulin and neurogranin govern the dynamics of CaMKII as a leaky integrator.

Calmodulin-dependent kinase II (CaMKII) has long been known to play an important role in learning and memory as well as long term potentiation (LTP). More recently it has been suggested that it might be involved in the time averaging of synaptic signals, which can then lead to the high precision of information stored at a single synapse. However, the role of the scaffolding molecule, neurogranin (Ng), in governing the dynamics of CaMKII is not yet fully understood. In this work, we adopt a rule-based modeling approach through the Monte Carlo method to study the effect of Ca2+ signals on the dynamics of CaMKII phosphorylation in the postsynaptic density (PSD). Calcium surges are observed in synaptic spines during an EPSP and back-propagating action potential due to the opening of NMDA receptors and voltage dependent calcium channels. Using agent-based models, we computationally investigate the dynamics of phosphorylation of CaMKII monomers and dodecameric holoenzymes. The scaffolding molecule, Ng, when present in significant concentration, limits the availability of free calmodulin (CaM), the protein which activates CaMKII in the presence of calcium. We show that Ng plays an important modulatory role in CaMKII phosphorylation following a surge of high calcium concentration. We find a non-intuitive dependence of this effect on CaM concentration that results from the different affinities of CaM for CaMKII depending on the number of calcium ions bound to the former. It has been shown previously that in the absence of phosphatase, CaMKII monomers integrate over Ca2+ signals of certain frequencies through autophosphorylation (Pepke et al, Plos Comp. Bio., 2010). We also study the effect of multiple calcium spikes on CaMKII holoenzyme autophosphorylation, and show that in the presence of phosphatase, CaMKII behaves as a leaky integrator of calcium signals, a result that has been recently observed in vivo. Our models predict that the parameters of this leaky integrator are finely tuned through the interactions of Ng, CaM, CaMKII, and PP1, providing a mechanism to precisely control the sensitivity of synapses to calcium signals. Author Summary not valid for PLOS ONE submissions.

Arterial baroreflex regulation of muscle sympathetic single-unit activity in men: influence of resting blood pressure.

The arterial baroreflex has dominant control over multiunit muscle sympathetic nerve activity (MSNA) burst occurrence, but whether this extends to all single units or is influenced by resting blood pressure status is unclear. In 22 men (32 ± 8 yr), we assessed 68 MSNA single units during sequential bolus injections of nitroprusside and phenylephrine (modified Oxford). Sympathetic baroreflex sensitivity (sBRS) was quantified as the weighted negative linear regression slope between diastolic blood pressure (DBP) and single-unit spike firing probability and multiple spike firing. Strong negative linear relationships (r ≥ -0.50) between DBP and spike firing probability were observed in 63/68 (93%) single units (-2.27 ± 1.27%·cardiac cycle-1·mmHg-1 [operating range, 18 ± 8 mmHg]). In contrast, only 45/68 (66%) single units had strong DBP-multiple spike firing relationships (-0.13 ± 0.18 spikes·cardiac cycle-1·mmHg-1 [operating range, 14 ± 7 mmHg]). Participants with higher resting DBP (65 ± 3 vs. 77 ± 3 mmHg, P < 0.001) had similar spike firing probability sBRS (low vs. high, -2.08 ± 1.08 vs. -2.46 ± 1.42%·cardiac cycle-1·mmHg-1, P = 0.33), but a smaller sBRS operating range (20 ± 6 vs. 16 ± 9 mmHg, P = 0.01; 86 ± 24 vs. 52 ± 25% of total range, P < 0.001) and a higher proportion of single units without arterial baroreflex control outside this range [6/31 (19%) vs. 21/32 (66%), P < 0.001]. Participants with higher resting DBP also had fewer single units with arterial baroreflex control of multiple spike firing (79 vs. 53%, P = 0.04). The majority of MSNA single units demonstrate strong arterial baroreflex control over spike firing probability during pharmacological manipulation of blood pressure. Changes in single-unit sBRS operating range and control of multiple spike firing may represent altered sympathetic recruitment patterns associated with the early development of hypertension.NEW & NOTEWORTHY Muscle sympathetic single units can be differentially controlled during stress. In contrast, we demonstrate that 93% of single units maintain strong arterial baroreflex control during pharmacological manipulation of blood pressure. Interestingly, the operating range and proportion of single units that lose arterial baroreflex control outside of this range are influenced by resting blood pressure levels. Altered single unit, but not multiunit, arterial baroreflex control may represent changes in sympathetic recruitment patterns in early stage development of hypertension.

New Appearance of Fragmented QRS as a Predictor of Ventricular Arrhythmic Events in Patients With Hypertrophic Cardiomyopathy.

Multiple spikes in the QRS complex (fragmented QRS [fQRS]) on 12-lead electrocardiography have been associated with ventricular arrhythmic events (VAEs) in patients with hypertrophic cardiomyopathy (HCM). The aim of this study was to assess the association between new appearances of fQRS and cardiac events in patients with HCM.Methods and Results:The association between baseline fQRS and cardiac events, namely VAEs, heart failure-related hospitalization, and all-cause death, was evaluated retrospectively in 146 HCM patients (46 patients with fQRS, 100 without fQRS). The median follow-up was 5.3 years. Cardiac events occurred in 29 patients with baseline fQRS and 32 patients without baseline fQRS (63% vs. 32%; P<0.001). VAEs occurred in a significantly larger percentage of patients with than without baseline fQRS (54% vs. 23%, respectively; P<0.001). Of the 100 patients without baseline fQRS, 33 had a new appearance of fQRS during the 4.6-year follow-up, whereas 67 did not. VAEs occurred more frequently in the 33 patients with the appearance of fQRS than in those without (42% vs. 13%, respectively; P=0.001). Multivariable analysis showed that the new appearance of fQRS documented before VAEs was associated with VAEs (hazard ratio 4.29, 95% confidence interval 1.81-10.2; P=0.001). The new appearance of fQRS was associated with an increased risk of VAEs in HCM patients.

Boosting Throughput and Efficiency of Hardware Spiking Neural Accelerators Using Time Compression Supporting Multiple Spike Codes.

Spiking neural networks (SNNs) are the third generation of neural networks and can explore both rate and temporal coding for energy-efficient event-driven computation. However, the decision accuracy of existing SNN designs is contingent upon processing a large number of spikes over a long period. Nevertheless, the switching power of SNN hardware accelerators is proportional to the number of spikes processed while the length of spike trains limits throughput and static power efficiency. This paper presents the first study on developing temporal compression to significantly boost throughput and reduce energy dissipation of digital hardware SNN accelerators while being applicable to multiple spike codes. The proposed compression architectures consist of low-cost input spike compression units, novel input-and-output-weighted spiking neurons, and reconfigurable time constant scaling to support large and flexible time compression ratios. Our compression architectures can be transparently applied to any given pre-designed SNNs employing either rate or temporal codes while incurring minimal modification of the neural models, learning algorithms, and hardware design. Using spiking speech and image recognition datasets, we demonstrate the feasibility of supporting large time compression ratios of up to 16×, delivering up to 15.93×, 13.88×, and 86.21× improvements in throughput, energy dissipation, the tradeoffs between hardware area, runtime, energy, and classification accuracy, respectively based on different spike codes on a Xilinx Zynq-7000 FPGA. These results are achieved while incurring little extra hardware overhead.

Organic pollutants, heavy metals and toxicity in oil spill impacted salt marsh sediment cores, Staten Island, New York City, USA

Sediment cores from Staten Island's salt marsh contain multiple historical oil spill events that impact ecological health. Microtox solid phase bioassay indicated moderate to high toxicity. Multiple spikes of TPH (6524 to 9586 mg/kg) and Σ16 PAH (15.5 to 18.9 mg/kg) were co-incident with known oil spills. A high TPH background of 400–700 mg/kg was attributed to diffuse sources. Depth-profiled metals Cu (1243 mg/kg), Zn (1814 mg/kg), Pb (1140 mg/kg), Ni (109 mg/kg), Hg (7 mg/kg), Cd 15 (mg/kg) exceeded sediment quality guidelines confirming adverse biological effects. Changes in Pb206/207 suggested three metal contaminant sources and diatom assemblages responded to two contamination events. Organic and metal contamination in Saw Mill Creek Marsh may harm sensitive biota, we recommend caution in the management of the 20–50 cm sediment interval because disturbance could lead to remobilisation of pre-existing legacy contamination into the waterway.

Estimating Time-Varying Applied Current in the Hodgkin-Huxley Model

The classic Hodgkin-Huxley model is widely used for understanding the electrophysiological dynamics of a single neuron. While applying a low-amplitude constant current to the system results in a single voltage spike, it is possible to produce multiple voltage spikes by applying time-varying currents, which may not be experimentally measurable. The aim of this work is to estimate time-varying applied currents of different deterministic forms given noisy voltage data. In particular, we utilize an augmented ensemble Kalman filter with parameter tracking to estimate four different time-varying applied current parameters and associated Hodgkin-Huxley model states, along with uncertainty bounds in each case. We test the efficiency of the parameter tracking algorithm in this setting by analyzing the effects of changing the standard deviation of the parameter drift and the frequency of data available on the resulting time-varying applied current estimates and related uncertainty.

Nonlinear mechanism of excitatory autapse-induced reduction or enhancement of firing frequency of neuronal bursting

Excitatory and inhibitory effect always induces the enhancement and inhibitory effect of neural electronic activities, which is the common viewpoint of the modulations to the neural firing and plays important roles in the information processing of the nervous system. In the present paper, the Homoclinic/Homoclinic bursting pattern with alternation behavior between burst containing multiple spikes and subthreshold oscillations and the tough value of the burst lower than that of the subthreshold oscillations is chosen as representative, and the excitatory effect on the complex nonlinear dynamics of the representative bursting pattern is studied. For the excitatory autapse with suitable autaptic time delay and strength, the autaptic current pulse applied to the trough of the burst can induce the number of spikes within a burst to decrease and then the average firing frequency to decline, which presents a novel example different from the common viewpoint of the excitatory effect. The excitatory autapse induces the average firing frequency to increase in the remained parameter region of two-parameter plane of the autaptic time delay and strength. With bifurcations acquired by the fast/slow variable dissection method and phase trajectory, the subthreshold oscillations of the bursting correspond to a subthreshold limit cycle of the fast subsystem and the spike within burst corresponds to a suprathreshold limit cycle, and excitatory autaptic current can induce the transition from suprathreshold limit cycle to subthreshold limit cycle, which leads the spike to terminate in advance and is the cause for reducing the average firing frequency. The results is the present paper are compared with the phenomenon and bifurcation mechanism that the excitatory autapse can induce the spike number to decrease within a burst but the average firing frequency to increase as indicated in a recent study on the Fold/Homoclinic bursting. These results enrich the uncommon phenomenon of the neuronal electrical activities, reveal the underlying nonlinear mechanism, provide a new way to regulate the bursting pattern, and disclose the potential functions of the excitatory autapse.

A Supervised Learning Algorithm for Spiking Neurons Using Spike Train Kernel Based on a Unit of Pair-Spike

In recent years, neuroscientists have discovered that the neural information is encoded by spike trains with precise times. Supervised learning algorithm based on the precise times for spiking neurons becomes an important research field. Although many existing algorithms have the excellent learning ability, most of their mechanisms still have some complex computations and certain limitations. Moreover, the discontinuity of spiking process also makes it very difficult to build an efficient algorithm. This paper proposes a supervised learning algorithm for spiking neurons using the kernel function of spike trains based on a unit of pair-spike. Firstly, we comprehensively divide the intervals of spike trains. Then, we construct an optimal selection and computation method of spikes based on the unit of pair-spike. This method avoids some wrong computations and reduces the computational cost by using each effective input spike only once in every epoch. Finally, we use the kernel function defined by an inner product operator to solve the computing problem of discontinue spike process and multiple output spikes. The proposed algorithm is successfully applied to many learning tasks of spike trains, where the effect of our optimal selection and computation method is verified and the influence of learning factors such as learning kernel, learning rate, and learning epoch is analyzed. Moreover, compared with other algorithms, all experimental results show that our proposed algorithm has the higher learning accuracy and good learning efficiency.