Slow Excitation Research Articles

Characterizing the Access of Cholinergic Antagonists to Efferent Synapses in the Inner Ear

Stimulation of cholinergic efferent neurons innervating the inner ear has profound, well-characterized effects on vestibular and auditory physiology, after activating distinct ACh receptors (AChRs) on afferents and hair cells in peripheral endorgans. Efferent-mediated fast and slow excitation of vestibular afferents are mediated by α4β2*-containing nicotinic AChRs (nAChRs) and muscarinic AChRs (mAChRs), respectively. On the auditory side, efferent-mediated suppression of distortion product otoacoustic emissions (DPOAEs) is mediated by α9α10nAChRs. Previous characterization of these synaptic mechanisms utilized cholinergic drugs, that when systemically administered, also reach the CNS, which may limit their utility in probing efferent function without also considering central effects. Use of peripherally-acting cholinergic drugs with local application strategies may be useful, but this approach has remained relatively unexplored. Using multiple administration routes, we performed a combination of vestibular afferent and DPOAE recordings during efferent stimulation in mouse and turtle to determine whether charged mAChR or α9α10nAChR antagonists, with little CNS entry, can still engage efferent synaptic targets in the inner ear. The charged mAChR antagonists glycopyrrolate and methscopolamine blocked efferent-mediated slow excitation of mouse vestibular afferents following intraperitoneal, middle ear, or direct perilymphatic administration. Both mAChR antagonists were effective when delivered to the middle ear, contralateral to the side of afferent recordings, suggesting they gain vascular access after first entering the perilymphatic compartment. In contrast, charged α9α10nAChR antagonists blocked efferent-mediated suppression of DPOAEs only upon direct perilymphatic application, but failed to reach efferent synapses when systemically administered. These data show that efferent mechanisms are viable targets for further characterizing drug access in the inner ear.

High-frequency vibrational control of principal parametric resonance of a nonlinear cantilever beam: Theory and experiment

The effects of high-frequency parametric excitation on the principal parametric resonance of a nonlinear beam are studied both theoretically and experimentally. Only the first mode of vibration under simultaneous slow-fast parametric excitation is considered for investigation. The method of direct partition of motion yields slow dynamics of the system which is further analyzed by multiple time scale method to obtain the amplitude and phase response of the system. It is observed that the effective damping and stiffness of the system is significantly modified by the high frequency parametric excitation. The analysis reveals that the parametric resonance curve shifts towards the higher range of slow parametric excitation frequency due to high-frequency excitation. The peak resonant response decreases with the increasing value of the strength of the high frequency excitation and also beyond a critical value of the strength of the high-frequency excitation, the jump resonance is eliminated. Overall, it is found that the principal Parametric resonance can be effectively controlled and suppressed by high frequency excitation. Analytical results are validated by direct numerical simulations and experiments. For some parameter values, vibrational resonance is also observed in theory and experiment. The parametric vibrational resonance of a cantilever beam is not previously observed experimentally and thus, it is a new finding of the present study. The vibrational resonance is believed to be utilized in amplifying the response of parametrically driven microcantilever beams found in many microsystems applications.

Ion cyclotron resonance heating fast and slow wave excitation and power deposition in edge plasmas with application to ITER

The antenna power coupling to the plasma centre and its possible deleterious coupling to the plasma edge are key parameters in an ion cyclotron resonance heating system. The influence on these parameters by the confluence between the slow and the fast magnetosonic waves is studied for the case of large machines. Until now, the modelling of the scrape off layer region has been calculated by ANTITER II, which contains only the fast wave description and where the confluence with the slow wave (S wave) is approximated by the Alfvén resonance. In the present study, a complete modelling of the slow and fast waves is made by ANTITER IV. The modelling by the two codes is compared and shows the important role of the Alfvén and the lower hybrid resonances for the excitation of large fields and associated power deposition at the edge of the plasma even far from the antenna location. The ANTITER IV modelling is thereafter applied to the case of the ITER antenna with a reference density profile and heating parameters. A comparative study is made for the edge power deposition and the excitation of large fields for different toroidal phasing cases of the antenna. This study also takes into account the tilting of the antenna array with respect to the total magnetic field in front of the antenna. If the Faraday screen is field-aligned, the excitation of the S wave occurs at the wave confluence; however, in the case of non-alignment the antenna directly excites the S wave. This effect is studied and quantified. All edge effects, even the direct excitation of S waves, can be strongly reduced by tailoring the current distribution in the straps of the antenna array. Resulting cases for the minimisation of edge power deposition in ITER and the reactor are studied.

Neuropeptides as Primary Mediators of Brain Circuit Connectivity.

Across sleep and wakefulness, brain function requires inter-neuronal interactions lasting beyond seconds. Yet, most studies of neural circuit connectivity focus on millisecond-scale interactions mediated by the classic fast transmitters, GABA and glutamate. In contrast, neural circuit roles of the largest transmitter family in the brain–the slow-acting peptide transmitters–remain relatively overlooked, or described as “modulatory.” Neuropeptides may efficiently implement sustained neural circuit connectivity, since they are not rapidly removed from the extracellular space, and their prolonged action does not require continuous presynaptic firing. From this perspective, we review actions of evolutionarily-conserved neuropeptides made by brain-wide-projecting hypothalamic neurons, focusing on lateral hypothalamus (LH) neuropeptides essential for stable consciousness: the orexins/hypocretins. Action potential-dependent orexin release inside and outside the hypothalamus evokes slow postsynaptic excitation. This excitation does not arise from modulation of classic neurotransmission, but involves direct action of orexins on their specific G-protein coupled receptors (GPCRs) coupled to ion channels. While millisecond-scale, GABA/glutamate connectivity within the LH may not be strong, re-assessing LH microcircuits from the peptidergic viewpoint is consistent with slow local microcircuits. The sustained actions of neuropeptides on neuronal membrane potential may enable core brain functions, such as temporal integration and the creation of lasting permissive signals that act as “eligibility traces” for context-dependent information routing and plasticity. The slowness of neuropeptides has unique advantages for efficient neuronal processing and feedback control of consciousness.

Tapping modes in the Atomic Force Microscope model with Lennard-Jones force and slow-fast base motion

Abstract Based on the idea of slow-fast dynamics, two tapping modes are investigated in the Atomic Force Microscope (AFM) model with Lennard-Jones force and slow-fast base motion. According to the approximation derived from Taylor expansion in the vicinity of static equilibrium of the linearized system, we give a prediction about harmonic responses of the fast sub-system (FSS). Then a truncated version of harmonic balancing method (HBM) is combined with the Floquet theory to give the distribution and stability of the harmonic responses, which indicates the contact and non-contact modes dominated by cycle manifolds. By directly integrating the FSS, the numerical bifurcation diagrams and the frequency spectrums corresponding to the periodic solutions are obtained to verify the results given by the half-analytic process. Moreover, distribution of basins of attraction shows that, when the tri-stability is destroyed by fold bifurcation of cycle, due to the highly fragmented fractal structures in basins, transition between different mode manifolds may present an weak irregular way. On the other hand, when the slow excitation is introduced, the regular and irregular “cycle-cycle” type mixed mode oscillations (MMOs) triggered by “fold of cycle/fold of cycle” hysteresis can be observed, which results in two tapping mode, .i.e., the slow tapping mode and the “compound of contact/snap tapping” mode. Besides that, our results show that, for the AFM under slow and near-resonant excitation, the beneficial effects of constant contact mode and snap tapping mode can be utilized.

The mammalian efferent vestibular system utilizes cholinergic mechanisms to excite primary vestibular afferents

Electrical stimulation of the mammalian efferent vestibular system (EVS) predominantly excites primary vestibular afferents along two distinct time scales. Although roles for acetylcholine (ACh) have been demonstrated in other vertebrates, synaptic mechanisms underlying mammalian EVS actions are not well-characterized. To determine if activation of ACh receptors account for efferent-mediated afferent excitation in mammals, we recorded afferent activity from the superior vestibular nerve of anesthetized C57BL/6 mice while stimulating EVS neurons in the brainstem, before and after administration of cholinergic antagonists. Using a normalized coefficient of variation (CV*), we broadly classified vestibular afferents as regularly- (CV* < 0.1) or irregularly-discharging (CV* > 0.1) and characterized their responses to midline or ipsilateral EVS stimulation. Afferent responses to efferent stimulation were predominantly excitatory, grew in amplitude with increasing CV*, and consisted of fast and slow components that could be identified by differences in rise time and post-stimulus duration. Both efferent-mediated excitatory components were larger in irregular afferents with ipsilateral EVS stimulation. Our pharmacological data show, for the first time in mammals, that muscarinic AChR antagonists block efferent-mediated slow excitation whereas the nicotinic AChR antagonist DHβE selectively blocks efferent-mediated fast excitation, while leaving the efferent-mediated slow component intact. These data confirm that mammalian EVS actions are predominantly cholinergic.

Subradiance of Cold and Dilute Atomic Ensembles Excited by Resonant Pulsed Radiation

The fluorescence dynamics of optically dense but dilute atomic ensembles cooled to sub-Doppler temperatures and excited by resonant pulsed radiation is studied. Apart from total radiation intensity, the temporal variations of the spectral composition of fluorescence and its polarization, as well as the variation of the spatial distribution of excitation in the atomic ensemble, are analyzed. Based on this analysis, it is shown that the role of radiation trapping becomes smaller with time, and subradiance quantum states formed as a result of the resonant dipole–dipole interatomic interaction become the main factor determining the slow atomic excitation decay. The dependence of the subradiance form on the ensemble size is analyzed.

Strain-induced crystallisation in natural rubber: a thermodynamically consistent model of the material behaviour using a serial connection of phases

A thermodynamically consistent concept to model the strain-induced crystallisation phenomenon using a multiphase approach is discussed in Loos et al. (CMAT 32(2):501–526,2020). In this follow-up contribution, the same mechanical framework is used to construct a second model that sets the same three phases in a serial connection, demonstrating an alternative to the former parallel connection of phases. The hybrid free energy is used to derive the constitutive equations. The evaluation of the Clausius–Duhem inequality ensures thermomechanical consistency. The model is based on a one-dimensional derivation that extends with the concept of representative directions to a three-dimensional anisotropic model. After the step-by-step derivation, the performance of the model is analysed in detail, including its comparison to the well-known Flory model, its evaluation for infinite fast and slow excitations, its simulation of uniaxial cycles and its validation via relaxation experiments. Finally, the model is compared comprehensively to the former parallel model showing their equivalent reason for existence.

Slow and sausage loop mode excitation due to local and global spontaneous perturbations

Aims. We analyse the capability of different types of perturbations associated with usual environment energy fluctuations of the solar corona to excite slow and sausage modes in solar flaring loops. Methods. We performed numerical simulations of magnetohydrodynamic ideal equations with a consideration of straight plasma magnetic tubes subject to local and global energy depositions. Results. We find that local loop energy depositions of typical microflares [∼(1027 − 1030) erg] are prone to driving slow shock waves that induce slow-mode patterns. The slow-mode features are obtained for every tested local energy deposition inside the loop. Meanwhile, in order to obtain an observable sausage mode pattern, a global perturbation that is capable of instantaneously modifying the internal loop temperature is required; specifically, the characteristic conductive heating time must be much smaller than the radiative cooling one. Experiments carried out by varying the parameter β demonstrate that the excitation of sausage modes does not significantly depend on the value of this parameter but, rather, depends on the global or local character of the energy source.

Slow-fast dynamics in the truss core sandwich plate under excitations with high and low frequencies

In this manuscript, slow-fast motions in a two degrees of freedom model under slow parametric and fast external excitations are analyzed using analytical and numerical methods. By expressing the state variables as the sums of slowly varying average and fast oscillations, the averaged equations which govern the slow dynamics for different magnitudes of external amplitude are obtained. For the averaged equations, analyzation about the equilibria and the corresponding stability shows that, the averaged slow manifolds constitute a pitchfork structure. Meanwhile, the harmonic balancing method is used to compute the slowly varying envelopes of the fast oscillations. On the other hand, bifurcation diagrams of the fast sub-system show structures in accordance with the pitchfork obtained from averaged equations as well as the amplitude curves computed by harmonic balancing method. Two forms of relative location between the folds of cycle on the handle and pitchfork bifurcation point are presented. Based on these, concerning on the slow-fast flow, two patterns of transition behavior between the handle and the upper (lower) branch of pitchfork namely “pitchfork/pitchfork” and “fold/pitchfork” types are analyzed, which indicate the dynamic buckling behaviors. Particularly, discussion about the influence of external excitation shows that, for case of near-resonant external frequency, increasing the amplitude of external excitation will change the local structures as well as the quantitative properties of the pitchfork, but holistic form of pitchfork type is a topological invariant.

Complex bursting patterns and fast-slow analysis in a smallest chemical reaction system with two slow parametric excitations

Abstract Present paper analyzes the bursting dynamics of a smallest chemical reaction system with multi-frequency slow parametric excitations (referred as SCRSMFSPEs hereafter), in which four novel bursting patterns, i. turnover-of-transcritical-hysteresis-induced bursting, ii. cascaded transcritical-hysteresis bursting, iii. turnover-of-transcritical-hysteresis/supHopf-induced compound bursting and iv. cascaded “supHopf/supHopf” bursting via “delayed transcritical/transcritical” hysteresis loop can be observed. Compared to the original system with a single slow parametric excitation, the hysteresis behavior displays complex dynamical characteristics when an additional parametric excitation is introduced. Typically, the non-zero equilibrium branch, may become the one with twists and turns, leading to more large amplitude oscillations appearing in the active phase of bursting. Based on this, we reveal the novel bursting patterns i and iii. Besides, we show that the non-zero equilibrium branch may cross the zero equilibrium and the supercritical Hopf bifurcation line spirally, resulting in additional transcritical bifurcation points and supercritical Hopf bifurcation points. This gives rise to multiple transcritical-bifurcation-delay-induced hysteresis behaviors, and another two bursting patterns ii and iv are created. Finally, we investigate the transition of these novel bursting, which shows that the transition of bursting is closely related to the excitation amplitudes.

Mixed mode oscillations induced by bi-stability and fractal basins in the FGP plate under slow parametric and resonant external excitations

In this paper, three patterns of mixed mode oscillations (MMOs) in the functionally graded piezoelectric (FGP) plate are analyzed. By introducing a slow axial excitation into the two degrees of freedom model, a fast-slow dynamic system with slow parametric and resonant external excitation is established. Using the resonance relations and the multiple scales method, the averaged equations as well as the approximation of stationary responses of the fast sub-system (FSS) are obtained. Thus, predictions of the possible distribution of periodic solutions are given for both two modes. Then numerical bifurcation diagrams of the FSS with respect to the control parameter are computed. It is shown that the FSS can present the coexistence of the stable limit cycle with small amplitude and the multi-period cycle with large amplitude. What is more, the amplitude of the external excitation has little qualitative effects on the bifurcation structure of the FSS. On the other hand, for different amplitude of the external excitation, three patterns of MMOs in the fast-slow system are observed. To explain the corresponding generation mechanisms, fast-slow analysis and basins of attraction (BOAs) of the FSS are combined to depict the transition behaviors of the fast-slow flow. Our results show that, as the amplitude of the external excitation increases, in the vicinity of the small amplitude cycle, the basin of attraction (BOA) of the big amplitude cycle will expand. Meanwhile, since the BOAs possess fractal structures, destinations of these transitions can show three patterns, namely cycle with small amplitude, multi-period cycle with large amplitude, hybrid of small/big cycle. Based on these, generation mechanisms of three MMOs patterns, which can be named as “cycle-chaos-cycle” MMOs, “cycle-chaos-big cycle” MMOs, “cycle-chaos-hybrid of small/big cycle” MMOs, are explained from a numerical view.

Effects of Different Fast Periodic Excitations on the Pitchfork Bifurcation and Vibrational Resonance

We investigate the effects on the pitchfork bifurcation and the vibrational resonance of an overdamped bistable system subjected to both a slow harmonic excitation and a fast periodic excitation with different waveforms. We use numerical simulations along with theoretical explanations to analyze some interesting phenomena. The bifurcation configuration depends closely on the form of the fast excitation. As a result, we have found that the key factor to influence the bifurcation configuration is the symmetry property of the fast excitation. Further, due to the relationship of the vibrational resonance with the pitchfork bifurcation, the vibrational resonance also depends closely on the form of the fast periodic excitation. Moreover, for anharmonic fast excitations, if it is asymmetric, the vibrational resonance usually depends closely on the initial conditions.

Complex aperiodic mixed mode oscillations induced by crisis and transient chaos in a nonlinear system with slow parametric excitation

For dynamic systems with multiple time scales, its long-term behaviors usually present as mixed mode oscillations (MMOs). The formation of MMOs is closely related to the fast transitions evoked by the bifurcations of the fast sub-system. Up till now, most of the results reported in deterministic systems focus on periodic MMOs, namely the holistic structure of waveform shows periodicity, no matter whether the slow manifolds that the fast–slow flow follows are periodic or not. Moreover, since the motion of the fast–slow flow is modulated by the critical manifolds, qualitative influences of transient behaviors on the holistic structure of MMOs are less concerned. While in this paper, three patterns of aperiodic MMOs are analyzed based on a three-dimensional nonautonomous system under slow parametric excitation. According to the types of manifolds among which the fast transitions take place, these MMOs can be named as aperiodic “cycle-chaos-cycle” MMOs, aperiodic “cycle-chaos-cycle” MMOs with additional chaotic bursters, and aperiodic “chaos-cycle-point” MMOs. By combining the fast–slow analysis on certain time intervals and the probe into the transient chaos near boundary crisis, generation mechanisms of these MMOs are investigated. Our results show that the relative location between the boundary crisis value and the minimum of slow variable will qualitatively change the pattern of large amplitude oscillations (LAOs); thus, the composition of bursters can be decided by the intensity of transient chaos. On the other hand, the small amplitude oscillations (SAOs) evoked by interior crisis may contain inner structures related to bifurcation delay and sharding phenomenon. Particularly, interior crisis can lead to merging phenomena of chaotic attractors. Thus, when the chaotic LAOs stages are over, the fast–slow flow can transit to upper or lower branch in a irregular way, which results in the uncertain locations of SAOs.

Compound relaxation oscillations connected by pulse-shaped explosion

Relaxation oscillations are ubiquitous in various fields of natural science and engineering technology. Exploring possible routes to relaxation oscillations is one of the important issues in the study of relaxation oscillations. Recently, the pulse-shaped explosion (PSE), a novel mechanism which can lead to relaxation oscillations, has been reported. The PSE means pulse-shaped sharp quantitative changes related the variation of system parameters in branches of equilibrium points and limit cycles, which leads the system’s trajectory to undertake sharp transitions and further induces relaxation oscillations. Regarding externally and parametrically excited nonlinear systems with different frequency ratios, some work on PSE has been reported. The present paper focuses on the PSE and the related relaxation oscillations in a externally and parametrically excited Mathieu-van der Pol-Duffing system. We show that if there is an initial phase difference between the slow excitations with the same frequency ratio, the fast subsystem may compose of two parts with different expressions, each of which determines a different vector field. As a result, the bistable behaviors are observed in the system. In particular, one of the vector fields exhibits two groups of bifurcation behaviors, which are symmetric with respect to the positive and negative PSE, and each can induce a cluster in the relaxation oscillations. Based on this, we present several routes to compound relaxation oscillations, and obtain new types of relaxation oscillations connected by pulse-shaped explosion, which we call compound “subHopf/fold-cycle” relaxation oscillations and compound “supHopf/supHopf” relaxation oscillations, respectively. Our results show that the two clusters in the resultant relaxation oscillations are connected by the PSE, and the initial phase difference plays an important role in transitions to different attractors and the generation of relaxation oscillations. Although the research in this paper is based on a specific nonlinear system, we would like to point out that the bistable behaviors, the PSE and the resultant compound relaxation oscillations can also be observed in other dynamical systems. The reason is that the fast subsystem composes of two different vector fields induced by the initial phase difference, which dose not rely on a specific system. The results of this paper deepen the research about PSE as well as the complex dynamics of relaxation oscillations.

Bursting oscillations induced by bistable pulse-shaped explosion in a nonlinear oscillator with multiple-frequency slow excitations

This paper investigates bursting dynamics of a Rayleigh oscillator with multiple-frequency slow excitations, in which two different bursting patterns related to the bistable pulse-shaped explosion (PSE) are obtained. Typically, the PSE, a novel sharp transition behavior reported recently, can be observed in the Rayleigh oscillator. We show that if there is an initial phase difference $$-\frac{\pi }{2}$$ between the slow excitations, two coexisting solution branches exhibiting PSE, which we call bistable PSE, may be created in the fast subsystem. Then, the route to bursting by the bistable PSE is analyzed, and two different bursting patterns, i.e., bursting of point–point type and bursting of cycle–cycle type, are obtained. Our findings show that the initial phase difference of excitations may have great effects on PSE, which thus plays an important role in transitions to different attractors and complex bursting dynamics.

Molecules probed with a slow chirped-pulse excitation: Analytical model of the free-induction-decay signal

Most chirped-pulse experiments refer to a theoretical study from McGurk, Schmalz, and Flygare [J. Chem. Phys. 60, 4181 (1974)] which is well tailored to interpret the signals obtained with very fast chirped pulses, but is not sufficient to account for the signals in the case of slower chirped pulses used in spectroscopy to increase the signal-to-noise ratio. A theoretical study of the polarization of molecules subjected to a chirped pulse in a cell, uniform supersonic flow, or molecular beam is presented. Three degrees of approximation for the polarization are introduced and are compared with the numerical solution of the optical Bloch equations. These expressions enter the analytic expression of the free-induction-decay signal which is validated against experimental data on the rotational emission spectra of OCS molecules. A relation among the pulse duration, the line position in the chirped pulse, and the signal amplitude is proposed in the thermalized case. It assists in the optimization of the chirped-pulse parameters and in the estimation of the error associated with the line intensity.

Bursting oscillations in Sprott B system with multi-frequency slow excitations: two novel “Hopf/Hopf”-hysteresis-induced bursting and complex AMB rhythms

Bursting oscillations in systems with multi-frequency slow excitations reflect multi-timescale dynamics. As there exist many kinds of multiple periodic excitations in actual dynamical systems, the analysis of dynamical behavior of such systems has received much attention. In this article, we first investigate the bursting in Sprott B system with a single excitation. We show that Hopf bifurcation delay may exhibit due to the effect of slow passage through the supercritical Hopf bifurcation. Interestingly, such delay behavior leads to a pinched “Hopf/Hopf”-hysteresis bursting when delay time is long enough. Then, we focus on the effects of the additional excitation $${\beta _2}{\mathrm{cos(}}{\omega _2}{\mathrm{t)}}$$ on the zero-crossing pinched “Hopf/Hopf”-hysteresis bursting. We find that, under the effects of $${\beta _2}{\mathrm{cos(}}{\omega _2}{\mathrm{t)}}$$ , “Hopf/Hopf”-bifurcation-delay-induced hysteresis behaviors may exhibit very interesting dynamical characteristics. In particular, each equilibrium branch may become the one with twists and turns. Then, the novel bursting pattern, turnover-of-zero-crossing pinched-“Hopf/Hopf”-hysteresis-induced bursting, is disclosed accordingly. In addition, we show that the equilibrium branches may cross each other spirally, leading to multiple intersection points under certain parameter conditions. There are two Hopf bifurcation points perching separately upon either side of the intersection points. This creates multiple delay-induced hysteresis behavior, and the other novel bursting pattern, cascaded pinched “Hopf/Hopf”-hysteresis bursting, is thus created. Finally, we investigate the complex amplitude-modulated bursting (CAMB) rhythms in Sprott B system with multi-frequency slow excitations.

Quasi-periodic bursters and chaotic dynamics in a shallow arch subject to a fast–slow parametric excitation

In this paper, various nonlinear dynamics of a one-degree-of-freedom shallow arch model are investigated. The arch is subject to an imposed displacement of its support that is composed of slow and fast harmonic motions. The corresponding mathematical model consists of a nonlinear quasi-periodic Mathieu–Duffing equation. The dynamics are analyzed using the singular perturbation theory and the Melnikov method. It is shown that invariant slow manifolds of the averaged system, over the fast dynamics, are slaving the dynamics of the system under the condition of non-hyperbolicity of the undeformed state of the arch. These manifolds correspond to the buckled, the unbuckled and the undeformed solutions of the arch. Various kinds of quasi-periodic and chaotic bursters relating these slow manifolds are obtained, and quasi-periodic bursters doubling and tripling sequences leading to hysteretic chaos are observed. Using the Melnikov method and the Lyapunov exponents computations, it was demonstrated that chaos induced by the slow excitation can be suppressed by the fast harmonic excitation in large domains of the control parameters space, especially in the regions where the undeformed configuration of the arch is not hyperbolic.

Slow NMDA-Mediated Excitation Accelerates Offset-Response Latencies Generated via a Post-Inhibitory Rebound Mechanism.

In neural circuits, action potentials (spikes) are conventionally caused by excitatory inputs whereas inhibitory inputs reduce or modulate neuronal excitability. We previously showed that neurons in the superior paraolivary nucleus (SPN) require solely synaptic inhibition to generate their hallmark offset response, a burst of spikes at the end of a sound stimulus, via a post-inhibitory rebound mechanism. In addition SPN neurons receive excitatory inputs, but their functional significance is not yet known. Here we used mice of both sexes to demonstrate that in SPN neurons, the classical roles for excitation and inhibition are switched, with inhibitory inputs driving spike firing and excitatory inputs modulating this response. Hodgkin–Huxley modeling suggests that a slow, NMDA receptor (NMDAR)-mediated excitation would accelerate the offset response. We find corroborating evidence from in vitro and in vivo recordings that lack of excitation prolonged offset-response latencies and rendered them more variable to changing sound intensity levels. Our results reveal an unsuspected function for slow excitation in improving the timing of post-inhibitory rebound firing even when the firing itself does not depend on excitation. This shows the auditory system employs highly specialized mechanisms to encode timing-sensitive features of sound offsets which are crucial for sound-duration encoding and have profound biological importance for encoding the temporal structure of speech.