Coherent Spike Research Articles

The vitals for steady nucleation maps of spontaneous spiking coherence in autonomous two-dimensional neuronal networks

Thin pancake-like neuronal networks cultured on top of a planar microelectrode array have been extensively tried out in neuroengineering, as a substrate for the mobile robot’s control unit, i.e., as a cyborg’s brain. Most of these attempts failed due to intricate self-organizing dynamics in the neuronal systems. In particular, the networks may exhibit an emergent spatial map of steady nucleation sites (“n-sites”) of spontaneous population spikes. Being unpredictable and independent of the surface electrode locations, the n-sites drastically change local ability of the network to generate spikes. Here, using a spiking neuronal network model with generative spatially-embedded connectome, we systematically show in simulations that the number, location, and relative activity of spontaneously formed n-sites (“the vitals”) crucially depend on the samplings of three distributions: (1) the network distribution of neuronal excitability, (2) the distribution of connections between neurons of the network, and (3) the distribution of maximal amplitudes of a single synaptic current pulse. Moreover, blocking the dynamics of a small fraction (about 4%) of non-pacemaker neurons having the highest excitability was enough to completely suppress the occurrence of population spikes and their n-sites. This key result is explained theoretically. Remarkably, the n-sites occur taking into account only short-term synaptic plasticity, i.e., without a Hebbian-type plasticity. As the spiking network model used in this study is strictly deterministic, all simulation results can be accurately reproduced. The model, which has already demonstrated a very high richness-to-complexity ratio, can also be directly extended into the three-dimensional case, e.g., for targeting peculiarities of spiking dynamics in cerebral (or brain) organoids. We recommend the model as an excellent illustrative tool for teaching network-level computational neuroscience, complementing a few benchmark models.

Stochastic transition in synchronized spiking nanooscillators

This work reports that synchronization of Mott material-based nanoscale coupled spiking oscillators can be drastically different from that in conventional harmonic oscillators. We investigated the synchronization of spiking nanooscillators mediated by thermal interactions due to the close physical proximity of the devices. Controlling the driving voltage enables in-phase 1:1 and 2:1 integer synchronization modes between neighboring oscillators. Transition between these two integer modes occurs through an unusual stochastic synchronization regime instead of the loss of spiking coherence. In the stochastic synchronization regime, random length spiking sequences belonging to the 1:1 and 2:1 integer modes are intermixed. The occurrence of this stochasticity is an important factor that must be taken into account in the design of large-scale spiking networks for hardware-level implementation of novel computational paradigms such as neuromorphic and stochastic computing.

Tungsten trioxide nanocomposite for conventional soliton and noise-like pulse generation in anomalous dispersion laser cavity

Abstract This work demonstrates the employment of tungsten trioxide/polydimethylsiloxane nanocomposite saturable absorber (WO3/PDMS-SA) in realizing mode-locked conventional soliton (CS) and noise-like pulse (NLP) laser generation in net anomalous dispersion. The switching formation from CS regime of 970.0 fs pulse duration to NLP regime of 182.0 fs coherent spike with 65.3 ps pedestal was achieved by varying its pump power. The pulse laser exhibited good stability of 50.76 and 49.82 dB signal-to-noise ratio at 9.09 MHz fundamental repetition rate and trivial variation during stability test for CS and NLP regime, respectively. This work expresses the feasibility of WO3/PDMS-SA in attaining various types of mode-locked pulse phenomena using a fixed cavity configuration conceivably beneficial for compact dual-purpose laser systems.

High power noise-like pulse at 2 μm and its applications in mid-IR Raman light and flat supercontinuum

Herein, a high-power noise-like (NL) pulse fiber laser system in the 2 μm region and its applications in mid-IR Raman stokes light and flat supercontinuum (SC) were experimentally demonstrated. An all-PM fiber configuration oscillator was constructed as the seed source which can deliver stable NL mode-locked pulse trains centered at ∼1950 nm wavelength with ∼5.37 MHz repetition rate. The pulse envelope and coherence spike widths of the NL pulse can be tunable from ∼2.5 ns to ∼3.4 ns and ∼397 fs to ∼375 fs, respectively. Relying on the magnified NL pulse, the cascaded Raman shifted stokes lights centered at ∼2148 nm and ∼2359 nm were separately achieved. Meanwhile, a flat SC with a 10 dB bandwidth of ∼480 nm (from ∼1940 nm to ∼2420 nm) was obtained after boosting in a large-mode-area fiber amplifier stage, and the average output power of ∼72 W represents the highest output power of the NL pulse in the 2 μm region, to the best of our knowledge. Moreover, we noted that the NL pulse-based spectrum broadening is much more effective than that the picosecond pulse-based. Our experimental results strongly imply that the NL pulse can be severed as an ideal laser source for the application of mid-IR spectroscopy.

Q-switched and noise-like mode-locked fiber laser based on ternary transition-metal carbide Nb2AlC saturable absorber

The saturable absorption of layered ternary transition-metal carbide (MAX) Nb2AlC is investigated in this work. Nb2AlC-based saturable absorber (SA) device is prepared and applied in an Er-doped fiber laser (EDFL). The EDFL can generate Q-switched and noise-like mode-locked pulses based on the excellent Nb2AlC SA. The EDFL operates in a Q-switched pulses mode state when the pump power is up to a threshold value of 50 mW. For the Q-switched pulse, the maximum single pulse energy is 66 nJ. The laser pulse generation mode switches to a noise-like mode-locked state when the pump power increases to 170 mW. The coherent spike duration is 2.8 ps and the corresponding maximum single pulse energy is 1.5 nJ at a pump power of 439 mW. A preliminary review of available literature indicates no reports of layered ternary carbide Nb2AlC as SA in an EDFL to generate switchable laser pulse modes. Results of this study suggest that ternary MAX Nb2AlC can be a remarkable nonlinear optical (NLO) device to explore switchable laser pulse generation modes and can encourage further studies on the ternary transition-metal carbides.

Experimental demonstration of coherent photonic neural computing based on a Fabry–Perot laser with a saturable absorber

As Moore’s law has reached its limits, it is becoming increasingly difficult for traditional computing architectures to meet the demands of continued growth in computing power. Photonic neural computing has become a promising approach to overcome the von Neuman bottleneck. However, while photonic neural networks are good at linear computing, it is difficult to achieve nonlinear computing. Here, we propose and experimentally demonstrate a coherent photonic spiking neural network consisting of Mach–Zehnder modulators (MZMs) as the synapse and an integrated quantum-well Fabry–Perot laser with a saturable absorber (FP-SA) as the photonic spiking neuron. Both linear computation and nonlinear computation are realized in the experiment. In such a coherent architecture, two presynaptic signals are modulated and weighted with two intensity modulation MZMs through the same optical carrier. The nonlinear neuron-like dynamics including temporal integration, threshold, and refractory period are successfully demonstrated. Besides, the effects of frequency detuning on the nonlinear neuron-like dynamics are also explored, and the frequency detuning condition is revealed. The proposed hardware architecture plays a foundational role in constructing a large-scale coherent photonic spiking neural network.

Conserved Population Dynamics in the Cerebro-Cerebellar System between Waking and Sleep.

Despite the importance of the cerebellum for motor learning, and the recognized role of sleep in motor memory consolidation, surprisingly little is known about neural activity in the sleeping cerebro-cerebellar system. Here, we used wireless recording from primary motor cortex (M1) and the cerebellum in three female monkeys to examine the relationship between patterns of single-unit spiking activity observed during waking behavior and in natural sleep. Across the population of recorded units, we observed similarities in the timing of firing relative to local field potential features associated with both movements during waking and up state during sleep. We also observed a consistent pattern of asymmetry in pairwise cross-correlograms, indicative of preserved sequential firing in both wake and sleep at low frequencies. Despite the overall similarity in population dynamics between wake and sleep, there was a global change in the timing of cerebellar activity relative to motor cortex, from contemporaneous in the awake state to motor cortex preceding the cerebellum in sleep. We speculate that similar population dynamics in waking and sleep may imply that cerebellar internal models are activated in both states, despite the absence of movement when asleep. Moreover, spindle frequency coherence between the cerebellum and motor cortex may provide a mechanism for cerebellar computations to influence sleep-dependent learning processes in the motor cortex.SIGNIFICANCE STATEMENT It is well known that sleep can lead to improved motor performance. One possibility is that off-line learning results from neural activity during sleep in brain areas responsible for the control of movement. In this study we show for the first time that neuronal patterns in the cerebro-cerebellar system are conserved during both movements and sleep up-states, albeit with a shift in the relative timing between areas. Additionally, we show the presence of simultaneous M1-cerebellar spike coherence at spindle frequencies associated with up-state replay and postulate that this is a mechanism whereby a cerebellar internal model can shape plasticity in neocortical circuits during sleep.

Solvent signals in two-dimensional electronic spectroscopy

We report on properties of non-resonant signals of several commonly used solvents in two-dimensional electronic spectroscopy. The signals can be split into three types with different evolution in population time: an initial, rather strong coherent spike with non-periodic oscillatory phase behavior, periodic oscillatory signals mostly connected to Raman-active vibrational modes of the solvents and non-oscillatory long lived signals. The relative amplitudes of the contributions depend on the solvent. We propose a simple model for predicting spectral positions of the non-resonant solvent signals. The results can be used to facilitate the identification and distinction of solvent and sample cell signals from the sample signal in two-dimensional electronic spectroscopy.

Effects of rTMS on working memory abilities and time-varying spectrum coherence of LFPS and spikes in rats

PurposeThe purpose of this study was to evaluate the effects of repetitive transcranial magnetic stimulation (rTMS) at different frequencies on working memory (WM) and neuroelectric activity in rats.Design/methodology/approachThree rTMS protocols involving different frequencies were applied to rats, and 16-channel local field potentials (LFPs) and spikes were recorded from the prefrontal cortex (PFC) of rats in each group during the WM task. First, the behavior of rats during the T-maze task was analyzed, and then, the firing rate of spikes and the energy of the θ-band and γ-band in LFPs when rats performed the WM tasks were calculated. Finally, the spectral coherence between LFPs and spikes was analyzed by wavelet transform.FindingsThe results showed that rats in the stimulation groups needed fewer days than those in the control group to reach the task correction standard during the WM experiment (p < 0.05). High-frequency rTMS increases the firing rate of spikes and the degree of synchronization of LFPs-spikes in the θ-band and γ-band in the WM process.Originality/valueThis study showed that high-frequency rTMS can improve the spatial learning ability of rats, which might be due to the increased neuronal excitability of the PFC and the enhancement of co-coding between different modes of neural signals. This study is helpful for understanding the neuroregulatory mechanism of rTMS and will provide a reference for the selection of a suitable frequency for TMS treatment.

Overcoming temporal dispersion for measurement of activity-related impedance changes in unmyelinated nerves

Objective. Fast neural electrical impedance tomography is an imaging technique that has been successful in visualising electrically evoked activity of myelinated fibres in peripheral nerves by measurement of the impedance changes (dZ) accompanying excitation. However, imaging of unmyelinated fibres is challenging due to temporal dispersion (TP) which occurs due to variability in conduction velocities of the fibres and leads to a decrease of the signal below the noise with distance from the stimulus. To overcome TP and allow electrical impedance tomography imaging in unmyelinated nerves, a new experimental and signal processing paradigm is required allowing dZ measurement further from the site of stimulation than compound neural activity is visible. The development of such a paradigm was the main objective of this study. Approach. A finite element-based statistical model of TP in porcine subdiaphragmatic nerve was developed and experimentally validated ex-vivo. Two paradigms for nerve stimulation and processing of the resulting data—continuous stimulation and trains of stimuli, were implemented; the optimal paradigm for recording dispersed dZ in unmyelinated nerves was determined. Main results. While continuous stimulation and coherent spikes averaging led to higher signal-to-noise ratios (SNRs) at close distances from the stimulus, stimulation by trains was more consistent across distances and allowed dZ measurement at up to 15 cm from the stimulus (SNR = 1.8 ± 0.8) if averaged for 30 min. Significance. The study develops a method that for the first time allows measurement of dZ in unmyelinated nerves in simulation and experiment, at the distances where compound action potentials are fully dispersed.

Noise‐like pulse generation with tungsten trioxide/polydimethylsiloxane‐clad microfiber saturable absorber

AbstractWe report the formation of noise‐like pulse (NLP) with tungsten trioxide/polydimethylsiloxane‐clad microfiber saturable absorber integrated in a ring‐cavity erbium‐doped fiber laser. The NLP operation was confirmed by the presence of a coherence spike on top of a broad pedestal in the autocorrelation trace, with the measured pulse width value of 410 fs and 3.56 ps respectively. By increasing the pump power from the mode‐locking threshold of 280–3300 mW, the spectral bandwidth was stretched from 22.3 to 22.8 nm, while the output power increased from to 1.9 to 24.3 mW. The maximum pulse energy of 3.5 nJ was generated at a repetition rate of 7 MHz. The signal‐to‐noise ratio was measured to be 53.8 dB, which indicated a good stability of pulse laser.

All-Polarization Maintaining Noise-Like Pulse From Mode-Locked Thulium-Doped Fiber Laser Based on Nonlinear Loop Mirror

In this paper, we present a figure-eight all-polarization maintaining thulium-doped mode-locked fiber laser based on a nonlinear optical loop mirror operating at noise-like pulse regimes. The total cavity length is 34.5 m, and the calculated net group delay dispersion is estimated to be ∼−2.616 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . At the maximum pump power, stable noise-like pulse centered at 1943 nm with a spectral full width at half maximum of 32 nm, a pulse energy of 13.51 nJ, and a coherence spike width of 236 fs is generated at a repetition rate of 5.96 MHz with the signal-to-noise ratio ∼64 dB. The polarization extinction ratio is > 15 dB at any mode-locking operation. The slope efficiency and the output power fluctuation of the laser are 5.16% and 0.039%, respectively. The laser does not require polarization state controllers, and it holds very high stability, which is insensitive to temperature changes or mechanical vibrations. Through further amplification, it will be a good laser source for real-time interrogation of fiber Bragg gratings and supercontinuum generation.

A neural circuit state change underlying skilled movements

In motor neuroscience, state changes are hypothesized to time-lock neural assemblies coordinating complex movements, but evidence for this remains slender. We tested whether a discrete change from more autonomous to coherent spiking underlies skilled movement by imaging cerebellar Purkinje neuron complex spikes in mice making targeted forelimb-reaches. As mice learned the task, millimeter-scale spatiotemporally coherent spiking emerged ipsilateral to the reaching forelimb, and consistent neural synchronization became predictive of kinematic stereotypy. Before reach onset, spiking switched from more disordered to internally time-locked concerted spiking and silence. Optogenetic manipulations of cerebellar feedback to the inferior olive bi-directionally modulated neural synchronization and reaching direction. A simple model explained the reorganization of spiking during reaching as reflecting a discrete bifurcation in olivary network dynamics. These findings argue that to prepare learned movements, olivo-cerebellar circuits enter a self-regulated, synchronized state promoting motor coordination. State changes facilitating behavioral transitions may generalize across neural systems.

10 µJ noise-like pulse generated from all fiberized Tm-doped fiber oscillator and amplifier.

Herein, we presented a high energy noise-like (NL) pulse Tm-doped fiber laser (TDFL) system. Relying on the nonlinear amplifying loop mirror (NALM), stable noise-like pulses with coherence spike width of ∼317 fs and envelope width of ∼4.2 ns were obtained from an all polarization-maintaining fiberized oscillator at central wavelength of ∼1946.4 nm with 3 dB bandwidth of ∼24.9 nm. After the amplification in an all-fiberized TDF amplifier system, the maximum average output power of ∼32.8 W and pulse energy of ∼10.1 µJ were obtained, which represents the highest pulse energy of NL pulse at ∼2 µm, to the best of our knowledge. We believe that the high energy NL pulse source has the potential application in mid-infrared supercontinuum generation.

Q-Switched and Noise-Like Mode Locked Er-Doped Fiber Laser Based on Nb2AlC Saturable Absorber

Nb 2 AlC is a kind of ternary ceramic material whose special crystal structure makes it both the advantages of metal and ceramics. And it has good electrical conductivity and strong stability at room temperature. In this article, the saturable absorption of Nb 2 AlC based thin film have been investigated, showing that it has saturated light intensity of 0.21 MW/cm 2 and the modulation depth of 2.62%. Noise-like mode locked and Q-switched pulses output based on Nb 2 AlC thin film have been achieved in erbium-doped fiber laser cavity. The narrowest width of noise-like mode-locked pulses' envelope is 13 ns, the maximum single pulse energy is 1.5 nJ, and the full width at half-maximum (FWHM) of the narrowest coherent spike is 2.34 ps. The minimum pulse width of the Q-switched pulse is 8.6 μs and the maximum single pulse energy is 66 nJ. As far as we know, this is the first report of Nb 2 AlC's application in ultrafast optics.

Purkinje Cell Activity Determines the Timing of Sensory-Evoked Motor Initiation

SummaryCerebellar neurons can signal sensory and motor events, but their role in active sensorimotor processing remains unclear. We record and manipulate Purkinje cell activity during a task that requires mice to rapidly discriminate between multisensory and unisensory stimuli before motor initiation. Neuropixels recordings show that both sensory stimuli and motor initiation are represented by short-latency simple spikes. Optogenetic manipulation of short-latency simple spikes abolishes or delays motor initiation in a rate-dependent manner, indicating a role in motor initiation and its timing. Two-photon calcium imaging reveals task-related coherence of complex spikes organized into conserved alternating parasagittal stripes. The coherence of sensory-evoked complex spikes increases with learning and correlates with enhanced temporal precision of motor initiation. These results suggest that both simple spikes and complex spikes govern sensory-driven motor initiation: simple spikes modulate its latency, and complex spikes refine its temporal precision, providing specific cellular substrates for cerebellar sensorimotor control.

Switchable generation of a sub-200 fs dissipative soliton and a noise-like pulse in a normal-dispersion Tm-doped mode-locked fiber laser.

We report on the switchable generation of a dissipative soliton (DS) pulse and a noise-like pulse (NLP) in an all-fiberized Tm-doped fiber laser in the normal-dispersion region. Mode-locking operation is achieved through a nonlinear polarization rotation component, and the cavity dispersion is compensated using ultra-high numerical aperture (UHNA4) fiber that is easy to integrate and low in cost. At a pump threshold of 510 mW, DS operation can first be achieved without additional filter. The 3 dB spectrum bandwidth of the DS pulse is greater than 50 nm, and the duration of the de-chirped pulse is 193 fs. By increasing the pump power to 880 mW, the mode-locking state can evolve into NLP operation with proper cavity polarization state. The 3 dB spectrum bandwidth and duration of de-chirped coherence spike are 105.6 nm and 121 fs, respectively. Meanwhile, ultra-broadband NLP (over 150 nm considering 3 dB spectrum width) can also be observed with the appropriate cavity parameters. All the proposed pulse patterns present good capacity for achieving narrow pulse width and withstanding high pulse energy.

SPARC: Method for Overcoming Temporal Dispersion in Unmyelinated Nerves for Imaging C Fibres with Electrical Impedance Tomography (EIT)

Fast neural EIT is a novel technique that enables imaging of evoked myelinated fibre activity in fascicles in rat sciatic nerve in vivo. However, imaging unmyelinated fibres is challenging due to temporal dispersion of the neural activity, caused by variability in fibre conduction velocities. This reduces the signal to below noise several centimetres from onset. The purpose of this work was to develop a method to overcome dispersion and allow EIT recordings of phasic activity at any distance from onset along the nerve.MethodsCompound impedance changes (dZ) were simulated using an electrically stimulated CAPs in 1D FEM model of a C fibre [1], with statistical analysis for 5000 fibres with conduction velocities 0.6±0.07 m/s (mean±SD) [2]. This enabled simulation of dZ up to 20 cm from the stimulus with stimulus trains of 5/10/20/50 Hz lasting 0.25–8 s with 3 s intervals between trains (Fig. 1a). The total duration of each simulation was 100 s.dZ was simulated 1) By coherent averaging of responses of supramaximal activity of single spikes [3] with demodulation bandwidth of 50–300 Hz and 2) By bandpass filtering of entire evoked spike trains with bandwidths of 0.25–5 Hz which allowed significant reduction of the noise without the need for coherent spike averaging.Random gaussian noise (0.015 μV RMS) was added to the signal to simulate realistic recording conditions. The SNR in the utilised approaches was computed for all tested stimulation and recording paradigms and compared.ResultsWhile coherent spike averaging was superior at short distances, its SNR fell exponentially with the distance from the onset (Fig. 1b, solid lines). The SNR with the compound demodulation was more consistent across distances (~2 at the optimal stimulation frequency of 20 Hz, Fig. 1b, dashed lines) allowing recording at ≥ 20 cm from stimulation. The estimated minimal averaging time required to obtain an SNR of 4 at 20 cm from the stimulus was equal to approximately 30 minutes at 20 Hz.Conclusion and future workThe developed stimulation and signal processing paradigm demonstrated the feasibility of dZ recording at long distances from the stimulus. Future work is to validate it on the ex vivo crustacean leg nerve model and subsequently an in vivo mammalian model with the final objective of imaging C fibres in the vagus nerve in humans. If successful, this technique will be applied for improvement of the emerging field of bioelectronic medicines [4].Support or Funding InformationThe work was supported by NIH SPARC grant no: 3OT2OD026545‐01S2.(a) Example of AP and dZ responses of the C fibre subjected to repetitive 50 Hz stimuli; (b) SNR computed for the single and compound recording paradigms.Figure 1

Excitatory/Inhibitory Responses Shape Coherent Neuronal Dynamics Driven by Optogenetic Stimulation in the Primate Brain.

Coherent neuronal dynamics play an important role in complex cognitive functions. Optogenetic stimulation promises to provide new ways to test the functional significance of coherent neural activity. However, the mechanisms by which optogenetic stimulation drives coherent dynamics remain unclear, especially in the nonhuman primate brain. Here, we perform computational modeling and experiments to study the mechanisms of optogenetic-stimulation-driven coherent neuronal dynamics in three male nonhuman primates. Neural responses arise from stimulation-evoked, temporally dynamic excitatory (E) and inhibitory (I) activity. Spiking activity is more likely to occur during E/I imbalances. Thus the relative difference in the driven E and I responses precisely controls spike timing by forming a brief time interval of increased spiking likelihood. Experimental results agree with parameter-dependent predictions from the computational models. These results demonstrate that optogenetic stimulation driven coherent neuronal dynamics are governed by the temporal properties of E/I activity. Transient imbalances in excitatory and inhibitory activity may provide a general mechanism for generating coherent neuronal dynamics without the need for an oscillatory generator.SIGNIFICANCE STATEMENT We examine how coherent neuronal dynamics arise from optogenetic stimulation in the primate brain. Using computational models and experiments, we demonstrate that coherent spiking and local field potential activity is generated by stimulation-evoked responses of excitatory and inhibitory activity in networks, extending the growing literature on neuronal dynamics. These responses create brief time intervals of increased spiking tendency and are consistent with previous observations in the literature that balanced excitation and inhibition controls spike timing, suggesting that optogenetic-stimulation-driven coherence may arise from intrinsic E/I balance. Most importantly, our results are obtained in nonhuman primates and thus will play a leading role in driving the use of causal manipulations with optogenetic tools to study higher cognitive functions in the primate brain.

Noise-Like Pulse Generation Using Polarization Maintaining Mode-Locked Thulium-Doped Fiber Laser With Nonlinear Amplifying Loop Mirror

We investigate noise-like pulse (NLP) generation in a mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror (NALM) and different net anomalous dispersions. The all-polarization maintaining (PM) fiber oscillator generates pulse trains with a frequency adjustable in the range of 4.06-20.4 MHz by utilizing different lengths of PM passive fiber in the NALM loop. An NLP with a coherence spike width of 232 fs was generated at 1993.6 nm with a 3-dB spectral width of 32.6 nm when the net cavity dispersion was -0.711 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .