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Neuromorphic Computing and Engineering

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Online ISSN: 2634-4386

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An RSNN performing a walk on a 23-state DFA, using noisy 1-bit weights. (a) The embedded DFA. If a binary number is input most-significant-bit first, the final state indicates the result of the input mod23. (b) The symbolic input to the RSNN. (c) The input vector to the RSNN at any time, which each masks out half of the neurons therein. Each different input s corresponds to a different hypervector s. Only the first 64 neurons are shown. (d) A spike raster plot of activity within the RSNN. When the input to the network is constant, the network stabilises in an attractor state. When the input changes, some blocks are masked out or revealed, which may cause transitions to a new attractor state. The block-WTA mechanism ensures that only one neuron is persistently active in each block. (e) The kernel-filtered mean firing rate of the neurons active in the attractor states q0,…,q22, as well as the transition-facilitating bridge states b0,…,b22. The bridge states are represented by dashed lines and coloured the same as their corresponding q attractor states. We here serially input the number 68 in binary format, and the RSNN correctly halts in the q22 state. (f) The same RSNN is given different sequences of inputs, and the RSNN performs the correct walk between attractor states in all cases.
The simulated RSNN with an irregular input timing scheme. (a) The symbolic input to the network. Inputs were given for between 200 and 1000 ms. (b) The corresponding input hypervector masking the neurons. (c) A raster plot of spike activity in the RSNN. (d) The mean firing rate of the neurons in each attractor state. The network is not reliant on an exact input timing scheme to perform the correct sequence of transitions. There is however still a minimum duration for which an input (or lack thereof) must be given, determined by the synaptic time constant.
The closed-loop experimental setup for running the RSNN using the 4096-device RRAM system. (a) A simplified schematic of the 64-neuron RSNN. (b) The physical RRAM measurement system, containing an FPGA board, three DAC boards, and one ADC board. (c) The scheme of running the closed-loop experiment in which the LIF neurons are simulated on a PC. The FPGA board receives the control commands from the PC and operates all word-, source- and bit lines (WLs, SLs, BLs) of the RRAM chip in parallel. At each time step (tn), the spikes generated by the neurons are sent to the synapse array on WLs, which are represented by voltage pulses. Meanwhile, a 0.2 V read voltage is applied to the SLs. The postsynaptic currents ( Itn) produced by the RRAM cells accumulate on each BL, and the readout results are returned to the PC through the ADCs and FPGA.
A 4-state DFA embedded into an RSNN using a memristive crossbar with 64 ×64 RRAM devices as the synaptic weights. The DFA is described by q0→sq1→sq2→sq3→sq0 for a single input s. (a) The ternary weight matrix to be written to the RRAM crossbar, and a histogram of the values. (b) Readout currents from each of the 64 ×64 RRAM devices after programming, and separate histograms for each of the ternary weight values. There is notable mismatch between the measured currents and the ideal values; a row of faulty devices giving almost no current; and devices giving anomalously large currents. (c) The masking input to the network. (d) A spike raster plot of the neurons within the RSNN. Due to the size constraints introduced by the crossbar, we chose the attractor hypervectors q to be orthogonal rather than random. (e) Measured postsynaptic current readings from whenever a neuron in the second block spiked, chosen for the prominence of trial-to-trial current variation. The weights between neurons in the same block were programmed to the lowest weight, hence the horizontal band of low currents. At some times, multiple neurons fired within the same time step (labelled by ∗). (f) The mean firing rates of the neurons in each attractor state. Despite the considerable nonidealities present, the RSNN performs the correct walk between attractor states.
The 23-state DFA on Intel’s asynchronous digital neuromorphic research chip, Loihi 2. (a) The input symbol to the network at any time, and (b) the corresponding input vectors, which mask the network activity. (c) A spike raster plot of the first 64 neurons. The shunting-inhibition WTA mechanism ensures that only one neuron in every block may spike at once (see Methods). (d) Kernel firing-rate estimates of each q and b state, choosing arbitrarily that 1 time step on Loihi represents 1 ms. The sequence of inputs given corresponds to the binary representation of the number 92. The RSNN halts in the q0 state, indicating correctly that 92 is divisible by 23. (e) For all sequences of inputs, the correct walk between attractor states is performed.

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Distributed representations enable robust multi-timescale symbolic computation in neuromorphic hardware

February 2025

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107 Reads

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1 Citation

Madison Cotteret

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Hugh Greatorex

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Aims and scope


Neuromorphic Computing and Engineering (NCE) is a multidisciplinary journal devoted to the design, development and application of artificial neural processing systems in advancing scientific discovery and realising emerging new technologies. Bringing together both the hardware and computational aspects of neuromorphic systems, the journal’s audience extends to engineering, materials science, physics, chemistry, biology, neuroscience and computer science across academia and industry.

Recent articles


(a) Mel and PEDOT:PSS chemical composition. (b) Schematic representation of synaptic OECTs based on Mel/PEDOT:PSS blends.
PPD of OECTs based on Mel/PEDOT:PSS blends. (a) Vpre (black curve) stimulus of 80 mV, tp = 10 ms, and Δt = 5 ms and respective Ipost response (blue curve) for an OECT prepared from a 1:4 blend. A1 and A2 correspond to the Ipost spikes elicited by the first and second voltage stimuli. ΔG as a function of (b) Δt, (c) tp, and (d) VPre for devices prepared from blends with different Mel/PEDOT:PSS ratios. The measurements were carried out using VPost = −100 mV.
Ten write-erase cycles after 50 pulses with magnitude Vpre = ± 0.3 V, width of 100 ms and interval of 30 ms (a), (c), (e), (g) and (i) or 100 ms (b), (d), (f), (h) and (j) for the pure PEDOT:PSS (a), (b), 1:9 (c), (d), 1:4 (e), (f), 1:2 (g), (h) and 1:1 (i), (j) OECTs.
Sets of 10, 20 or 50 write pulses with amplitude of +600 mV, tp = Δt = 500 ms followed by VPre = 0 V for pure (a) PEDOT:PSS, (b) 1:9, (c) 1:4, (d) 1:2 and (e) 1:1 OECTs. (f) ΔPSC decay over time after 50 write pulses. The postsynaptic voltage was set to −600 mV.
Melanin/PEDOT:PSS organic synaptic transistors: a step towards sustainable neuromorphic applications
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March 2025

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39 Reads

Inspired by the functioning of the human brain, organic synaptic transistors represent a promising avenue for developing neuromorphic technologies. However, achieving sustainability while maintaining performance and functionality remains a critical challenge. Here, we report on an innovative strategy where synthetic melanin (Mel)—a natural pigment known for its improved ionic–electronic coupling, high volumetric capacitance, and environmentally friendly characteristics—is blended with benchmark poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to fabricate synaptic transistors. Mel/PEDOT:PSS blends having different amounts of Mel have been systematically evaluated as semiconducting layer in organic electrochemical transistors. Our findings reveal that Mel incorporation at different concentrations enables tunable synaptic responses, such as enhanced memory retention and access to multiple memory states. These effects arise from the unique properties of Mel which modulate the charge density of PEDOT:PSS in a controlled manner. This approach demonstrates the potential for developing highly stable, multi-level memory materials for organic neuromorphic devices while addressing sustainability goals. We believe our strategy can open new avenues via the integration of natural and bio-inspired materials into organic semiconductors towards the development of sustainable neuromorphic technologies.


Tiny dLIF: A dendritic spiking neural network enabling a time-domain energy-efficient seizure detection system.

March 2025

Epilepsy poses a significant global health challenge, driving the need for reliable diagnostic tools like scalp electroencephalogram (EEG), subscalp EEG, and intracranial EEG (iEEG) for accurate seizure detection, localization, and modulation for treating seizures. However, these techniques often rely on feature extraction techniques such as Short Time Fourier Transform (STFT) for efficiency in seizure detection. Drawing inspiration from brain architecture, we investigate biologically plausible algorithms, specifically emphasizing time-domain inputs with low computational overhead. Our novel approach features two hidden layer dendrites with Leaky Integrate-and-Fire (dLIF) spiking neurons, containing fewer than 300K parameters and occupying a mere 1.5 MB of memory. Our proposed network is tested and successfully generalized on four datasets from the USA and Europe, recorded with different front-end electronics. USA datasets are scalp EEG in adults and children, and European datasets are iEEG in adults. All datasets are from patients living with epilepsy. Our model exhibits robust performance across different datasets through rigorous training and validation. We achieved AUROC scores of 81.0% and 91.0% in two datasets. Additionally, we obtained AUPRC and F1 Score metrics of 91.9% and 88.9% for one dataset, respectively. We also conducted out-of-sample generalization by training on adult patient data, and testing on children’s data, achieving an AUROC of 75.1% for epilepsy detection. This highlights its effectiveness across continental datasets with diverse brain modalities, regardless of montage or age specificity. It underscores the importance of embracing system heterogeneity to enhance efficiency, thus eliminating the need for computationally expensive feature engineering techniques like Fast Fourier Transform (FFT) and STFT.


Probabilistic computing with percolating nanoparticle networks using experimental data with signatures of criticality

March 2025

Percolating Networks of Nanoparticles (PNNs) are promising systems for neuromorphic computing due to their brain-like network structure and dynamics. In particular, electrical spiking in PNNs meets criteria for criticality, which is thought to be the operating point for biological brains and associated with optimal computation. Previous work showed through simulations that spiking PNNs can be used as the core stochastic component in a probabilistic computing scheme. Here, we demonstrate a route to experimental implementation of an integer factorization algorithm. We outline an important modification to the algorithm previously used and demonstrate factorization of up to six-digit integers. Finally, we explore the effect of criticality in the context of the integer factorization task by comparing critical and non-critical systems. We show significant differences in the probability distribution of states generated by the critical and non-critical systems, though all systems correctly factorize the integer of interest.


Combining SNNs with filtering for efficient neural decoding in implantable brain-machine interfaces

March 2025

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3 Reads

While it is important to make implantable brain-machine interfaces wireless to increase patient comfort and safety, the trend of increased channel count in recent neural probes poses a challenge due to the concomitant increase in the data rate. Extracting information from raw data at the source by using edge computing is a promising solution to this problem, with integrated intention decoders providing the best compression ratio. Recent benchmarking efforts have shown recurrent neural networks to be the best solution. Spiking Neural Networks (SNN) emerge as a promising solution for resource efficient neural decoding while Long Short Term Memory (LSTM) networks achieve the best accuracy. In this work, we show that combining traditional signal processing techniques, namely signal filtering, with SNNs improve their decoding performance significantly for regression tasks, closing the gap with LSTMs, at little added cost. Results with different filters are shown with Bessel filters providing best performance. Two block-bidirectional Bessel filters have been used–one for low latency and another for high accuracy. Adding the high accuracy variant of the Bessel filters to the output of ANN, SNN and variants provided statistically significant benefits with maximum gains of ≈5% and 8% in R² for two SNN topologies (SNN_Streaming and SNN_3D). Our work presents state of the art results for this dataset and paves the way for decoder-integrated-implants of the future.


Accelerating spiking neural networks with parallelizable leaky integrate-and-fire neurons

March 2025

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13 Reads

Spiking neural networks (SNNs) express higher biological plausibility and excel at learning spatiotemporal features while consuming less energy than conventional artificial neural networks, particularly on neuromorphic hardware. The leaky integrate-and-fire (LIF) neuron stands out as one of the most widely used spiking neurons in deep learning. However, its sequential information processing leads to slow training on lengthy sequences, presenting a critical challenge for real-world applications that rely on extensive datasets. This paper introduces the parallelizable LIF (ParaLIF) neuron, which accelerates SNNs by parallelizing their simulation over time, for both feedforward and recurrent architectures. Compared to LIF in neuromorphic speech, image and gesture classification tasks, ParaLIF demonstrates speeds up to 200 times faster and, on average, achieves greater accuracy with similar sparsity. When integrated into state-of-the-art architectures, ParaLIF’s accuracy matches or exceeds the highest performance reported in the literature on various neuromorphic datasets. These findings highlight ParaLIF as a promising approach for the development of rapid, accurate and energy-efficient SNNs, particularly well-suited for handling massive datasets containing long sequences.


On the sampling sparsity of analog-to-spike conversion based on leaky integrate-and-fire

March 2025

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12 Reads

In contrast to the traditional principle of periodic sensing, neuromorphic engineering pursues a paradigm shift towards bio-inspired event-based sensing, where events are primarily triggered by a change in the perceived stimulus. We show in a rigorous mathematical way that information encoding by means of Threshold-Based Representation based on either Leaky Integrate-and-Fire or Send-on-Delta is linked to an analog-to-spike conversion that guarantees maximum sparsity while satisfying an approximation condition based on the Alexiewicz norm.


(a) Schematic illustration of ECRAM device. Ions migrate vertically through the electrolyte under the influence of a gate voltage, modulating the conductance of the channel. (b) Schematic illustration of FeFET device. Gate voltage induces ferroelectric dipole alignment in the oxide layer, which modulates the carrier density in the channel.
(a) Schematic of the fabricated Cu-ion-actuated three-terminal ECRAM device. (b) Read current, measured at 0.5 V from the source to the drain of the Cu/HfOx/WOx (from top to bottom) stack as a function of the gate pulse. (c) Schematic of the CuOx/HfOx/WOx ECRAM device. (d) ΔG per pulse, corresponding to the CuOx gate composition. (a)–(d) Reprinted from [26], with the permission of AIP Publishing.
(a) Normalized channel current response for the HfOx electrolyte thickness dependence at each CuOx gate. (b) Normalized channel current as a function of working pressure during the HfOx electrolyte deposition (c) O 1s peak in the differently deposited HfOx layers. (a)–(c) Reprinted from [29], with the permission of AIP Publishing. (d) Schematic diagram, (e) cross-sectional transmission electron microscope (TEM) image of the fabricated CuOx/HfOx ECRAM device. (f) The update curve of the channel current in the ECRAM device uses an optimized HfOx electrolyte layer. (g) TEM image of the pristine CuOx/Al2O3/HfOx stack; elemental mapping of CuOx/Al2O3/HfOx ECRAM device following 100 potentiation pulses shows the Al2O3 layer being free of Cu ions which are being confined to the HfOx layer. (h) The update curve of the channel current in the CuOx/Al2O3/HfOx ECRAM device is programmed using the two-step programming pulse scheme. (d)–(h) Reproduced from [38]. CC BY 4.0. (i) The cycle-to-cycle characteristics of CuOx/Al2O3/HfOx ECRAM device.
(a) P–V hysteresis loops of HAO films as a function of the number of Al2O3 layer deposition steps. (b) The grazing incidence x-ray diffraction (GIXRD) patterns of HAO films with various numbers of Al2O3 layer deposition steps. (c) Cycling endurance for Al:HfO2 films, where three or four Al2O3 layer deposition steps were used. (d) Schematic of three stacks with different distributions of Al2O3 layer deposition steps. (e) P–V hysteresis obtained using the positive-up negative-down measurement technique for three types of HAO films. (a)–(e) Reprinted from [39], with the permission of AIP Publishing. (f) Device-to-device variation evaluated from 20 cells in device, where Al dopants were primarily distributed near the bottom electrode (BE).
(a) P–V hysteresis loops and (b) cross-sectional TEM images of the single HZO and HAO layers. (c) Vc response of the single and dual stacks. (d) P–V hysteresis loops and cross-sectional TEM images of two dual stacks such as HZO/HAO and HAO/HZO. (a)–(d) Reprinted from [40], with the permission of AIP Publishing. (e) Device-to-device variation evaluated from 13 cells. (f) Endurance characteristics of single stacks (HZO and HAO) and dual stacks (HZO/HAO and HAO/HZO). (g) Plausible mechanism for the two-step alignment process in dual stacks. (f), (g) Reprinted from [40], with the permission of AIP Publishing.
Optimizing electrochemical and ferroelectric synaptic devices: from material selection to performance tuning

February 2025

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31 Reads

Neuromorphic hardware systems emulate the parallel neural networks of the human brain, and synaptic weight storage elements are crucial for enabling energy-efficient information processing. They must represent multiple data states and be able to be updated analogously. In order to realize highly controllable synaptic devices, replacing the high-k gate dielectric in conventional transistor structures with either solid-electrolytes that facilitate bulk ionic motion or ferroelectric oxide allows for steady adjustment of channel currents in response to gate-voltage signals. This approach, in turn, accelerates backpropagation algorithms used for training neural networks. Furthermore, because the channel current in electrochemical random-access memory (ECRAM) is influenced by the number of mobile ions (e.g. Li⁺, O²⁻, H⁺ or Cu⁺) passing through the electrolytes, these synaptic device candidates have demonstrated an excellent linear and symmetrical channel current response when updated using an identical pulse scheme. In the latter case, which is known as the ferroelectric field-effect transistor (FeFET), the number of electrons accumulated near the channel rapidly varies with the degree of the alignment of internal dipoles in thin doped ferroelectric HfO2. This leads to a multilevel state. Based on the working principles of these two promising candidates, enabling gate-controlled ion-transport primarily in electrolytes for ECRAM and understanding the relationship between polarization and the ferroelectric layer in FeFETs are crucial to improve their properties. Therefore, this paper aims to present our recent advances, highlighting the engineering approaches and experimental findings related to ECRAM and FeFET for three-terminal synaptic devices.


Overview of Burstprop connectivity and signal transmission: A Schematic of the core spiking neural network architecture. Each neuron is modeled as a two-compartment model with a dendrite (rectangle) and soma (triangle). The inputs to the dendrites modulate burst generation while the input to the soma modulate event generation, which can be either a single spike or a burst. Axons for each principal cell (orange and yellow) can connect locally, to the layer above, or to the layer below. Axons can selectively propagate either events (orange) or bursts (yellow). When connections are made to a lower-level unit, they target the dendritic compartment. When connections are made to a higher-level unit, they connect to a somatic compartment. Somatic compartment controls the rate of events being generated while the dendritic compartment controls the ratio of such events that are bursts. The target representation is used to generate an error signal that is fed back to the dendrite of the top layer (black unit and connections). Dendrites also receive a regularization signal to control the event rate (blue connections). B Schematic of network for performing MNIST-like tasks. Images are flattened to a vector and pixel intensities are converted to spike train through Poisson firing. These form the input layer of the network whose detailed architecture is shown in A. A supervision is introduced at the readout layer where the firing in the desired unit is enforced by the creation of an error signal, injected in the readout units’ dendrites. C Schematic of the different types of feedback connectivity considered in this work. We used W0, W1 and W2 to label the feed forward weights from input, first layer or second layer, in the same order. These weights matrices are re-used for the feedback weights in the symmetric feedback scenario. In feedback alignement and direct FA, different weight matrices are used: B1, B2.
Dendritic potential steers direction of plasticity for synapses to neurons. A. Time-varying dendritic potential following a sine curve. B. Burst probabilities. Unsigned Burstprop, PB=σ(Vd). Signed Burstprop, PB+=max(0,tanh⁡(Vd)) and PB−=max(0,−tanh⁡(Vd)). C. Poisson spike train, with 50 Hz firing rate. D. Burst train generated from spike train and burst probability. E. Eligibility trace of a presynaptic neuron. F. Resultant synaptic plasticity.
Burstprop coordinates multilayer learning to solve MNIST. A. Comparing test classification error on spiking MNIST dataset for Signed Burstprop, Unsigned Burstprop, and BPTT with symmetric feedback for networks with an increasing number of hidden layers, 100 neurons per layer (A1), and networks with increasing layer width, 1 hidden layer (A2). Error bars are standard error of the mean over 10 initializations. Burstprop algorithms were trained for 100 epochs and BPTT was trained for 200 epochs. A3. Example learning curves for each algorithm on a network of 4 hidden layers, each with 100 neurons. Error bars represent the standard deviation of minimum test error for 10 simulations. B. Signed Burstprop test accuracy and mean square error (MSE) per 10³ samples of a single hidden layer neural network of 100 hidden neurons. Row 1: W0 learns and W1 is frozen. Row 2: W1 learns and W0 is frozen.
Burstprop learns with feedback alignment methods: A. Comparing test classification error on spiking MNIST dataset for different feedback error transportation methods with the Signed Burstprop (A1) and Unsigned Burstprop (A2) algorithms with increasing number of hidden neurons, 100 neurons per layer. Each trained for 100 epochs. Error bars are standard error of the mean over 10 initializations. A3. Example learning curves for each algorithm on a network of 4 hidden layers, each with 100 neurons. B. Signed Burstprop with FA test accuracy and mean square error (MSE) per 10³ samples of a single hidden layer neural network of 100 hidden neurons. Row 1: W0 learns and W1 is frozen. Row 2: W1 learns and W0 is frozen.
Burstprop is robust to low-resolution synaptic weights. A. Comparing test classification error on spiking MNIST dataset for networks of a single hidden layer of 100 neurons, trained with Signed Burstprop, with varying weight resolutions. Error bars are standard error of the mean over 10 initializations. B. Initial weight distributions of input weights for varying weight resolutions.
A burst-dependent algorithm for neuromorphic on-chip learning of spiking neural networks

February 2025

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9 Reads

The field of neuromorphic engineering addresses the high energy demands of neural networks through brain-inspired hardware for efficient neural network computing. For on-chip learning with spiking neural networks, neuromorphic hardware requires a local learning algorithm able to solve complex tasks. Approaches based on burst-dependent plasticity have been proposed to address this requirement, but their ability to learn complex tasks has remained unproven. Specifically, previous burst-dependent learning was demonstrated on a spiking version of the ‘exclusive or’ problem (XOR) using a network of thousands of neurons. Here, we extend burst-dependent learning, termed ‘Burstprop’, to address more complex tasks with hundreds of neurons. We evaluate Burstprop on a rate-encoded spiking version of the MNIST dataset, achieving low test classification errors, comparable to those obtained using backpropagation through time on the same architecture. Going further, we develop another burst-dependent algorithm based on the communication of two types of error-encoding events for the communication of positive and negative errors. We find that this new algorithm performs better on the image classification benchmark. We also tested our algorithms under various types of feedback connectivity, establishing that the capabilities of fixed random feedback connectivity is preserved in spiking neural networks. Lastly, we tested the robustness of the algorithm to weight discretization. Together, these results suggest that spiking Burstprop can scale to more complex learning tasks and is therefore likely to be considered for self-supervised algorithms while maintaining efficiency, potentially providing a viable method for learning with neuromorphic hardware.


ReSpike: residual frames-based hybrid spiking neural networks for efficient action recognition

February 2025

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6 Reads

Spiking Neural Networks (SNNs) have emerged as a compelling, energy-efficient alternative to traditional Artificial Neural Networks (ANNs) for static image tasks such as image classification and segmentation. However, in the more complex video classification domain, SNN-based methods fall considerably short of ANN-based benchmarks due to the challenges in processing dense frame sequences. To bridge this gap, we propose ReSpike, a hybrid framework that synergizes the strengths of ANNs and SNNs to tackle action recognition tasks with high accuracy and low energy cost. By partitioning film clips into RGB image Key Frames, which primarily capture spatial information, and event-like Residual Frames, which emphasize temporal dynamics cues, ReSpike leverages ANN for processing spatial features and SNN for modeling temporal features. In addition, we propose a multi-scale cross-attention mechanism for effective feature fusion. Compared to state-of-the-art SNN baselines, our ReSpike hybrid architecture demonstrates significant performance improvements (e.g. >30% absolute accuracy improvement on HMDB-51, UCF-101, and Kinetics-400). Furthermore, ReSpike achieves comparable performance with prior ANN approaches while bringing better accuracy-energy tradeoff. Code is shared at https://github.com/Intelligent-Computing-Lab-Yale/ReSpike.


Slax: a composable JAX library for rapid and flexible prototyping of spiking neural networks

February 2025

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15 Reads

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2 Citations

Spiking neural networks (SNNs) offer rich temporal dynamics and unique capabilities, but their training presents challenges. While backpropagation through time with surrogate gradients is the defacto standard for training SNNs, it scales poorly with long time sequences. Alternative learning rules and algorithms could help further develop models and systems across the spectrum of performance, bio-plausibility, and complexity. However, these alternatives are not consistently implemented with the same, if any, SNN framework, often complicating their comparison and use. To address this, we introduce Slax, a JAX-based library designed to accelerate SNN algorithm design and evaluation. Slax is compatible with the broader JAX and Flax ecosystem and provides optimized implementations of diverse training algorithms, enabling direct performance comparisons. Its toolkit includes methods to visualize and debug algorithms through loss landscapes, gradient similarities, and other metrics of model behavior during training. By streamlining the implementation and evaluation of novel SNN learning algorithms, Slax aims to facilitate research and development in this promising field.


Distributed representations enable robust multi-timescale symbolic computation in neuromorphic hardware

February 2025

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107 Reads

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1 Citation

Programming recurrent spiking neural networks (RSNNs) to robustly perform multi-timescale computation remains a difficult challenge. To address this, we describe a single-shot weight learning scheme to embed robust multi-timescale dynamics into attractor-based RSNNs, by exploiting the properties of high-dimensional distributed representations. We embed finite state machines into the RSNN dynamics by superimposing a symmetric autoassociative weight matrix and asymmetric transition terms, which are each formed by the vector binding of an input and heteroassociative outer-products between states. Our approach is validated through simulations with highly nonideal weights; an experimental closed-loop memristive hardware setup; and on Loihi 2, where it scales seamlessly to large state machines. This work introduces a scalable approach to embed robust symbolic computation through recurrent dynamics into neuromorphic hardware, without requiring parameter fine-tuning or significant platform-specific optimisation. Moreover, it demonstrates that distributed symbolic representations serve as a highly capable representation-invariant language for cognitive algorithms in neuromorphic hardware.


Neuromorphic compliant control facilitates human-prosthetic performance for hand grasp functions

February 2025

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17 Reads

Current bionic hands lack the ability of fine force manipulation for grasping fragile objects due to missing human neuromuscular compliance in control. This incompatibility between prosthetic devices and the sensorimotor system has resulted in a high abandonment rate of hand prostheses. To tackle this challenge, we employed a neuromorphic modeling approach, biorealistic control, to regain human-like grasping ability. The biorealistic control restored muscle force regulation and stiffness adaptation using neuromorphic modeling of the neuromuscular reflex units, which was capable of real-time computing of model outputs. We evaluated the dexterity of the biorealistic control with a set of delicate grasp tasks that simulated varying challenging scenarios of grasping fragile objects in daily activities of life, including the box and block task, the glass box task, and the potato chip task. The performance of the biorealistic control was compared with that of proportional control. Results indicated that the biorealistic control with the compliance of the neuromuscular reflex units significantly outperformed the proportional control with more efficient grip forces, higher success rates, fewer break and drop rates. Post-task survey questionnaires revealed that the biorealistic control reduced subjective burdens of task difficulty and improved subjective confidence in control performance significantly. The outcome of the evaluation confirmed that the biorealistic control could achieve superior abilities in fine, accurate, and efficient grasp control for prosthetic users.


Multilayer magnetic skyrmion devices for spiking neural networks

February 2025

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13 Reads

Spintronic devices -based on magnetic solitons, such as the domain wall motion and the skyrmions, have shown a significant potential for applications in energy-efficient data storage and beyond CMOS computing architectures. Based on the magnetic multilayer hetero-structures, we propose a magnetic skyrmion-magnetic tunnel junction device structure, mimicking leaky integrate and fire LIF neuron characteristics. The device is controlled by spin-orbit torque-SOT driven skyrmion motion in the ferromagnetic thin film. The modified leaky integrate and fire LIF neuron-like characteristics are shown using the combination of SOT and the skyrmion position dependence of the demagnetization energy. The device characteristics are modeled as the modified LIF neuron. The LIF neuron is one of the fundamental spiking neuron models; we integrate the model in the three-layer spiking neural network (SNN) and convolutional CSNN framework to test these spiking neuron models to classify the MNIST and FMNIST datasets. In both architectures, the network achieves classification accuracy above 97.10%. Additionally, the LIF neuron latency is in ns; thus, when integrated with the CMOS, the proposed device structures and associated systems exhibit an excellent future for energy-efficient neuromorphic computing.


Towards neuromorphic compression based neural sensing for next-generation wireless implantable brain machine interface

January 2025

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30 Reads

This work introduces a neuromorphic compression based neural sensing architecture with address-event representation inspired readout protocol for massively parallel, next-gen wireless implantable brain machine interface (iBMI). The architectural trade-offs and implications of the proposed method are quantitatively analyzed in terms of compression ratio (CR) and spike information preservation. For the latter, we used metrics such as root-mean-square error and correlation coefficient (CC) between the original and recovered signals to assess the effect of neuromorphic compression on the spike shape. Furthermore, we use accuracy, sensitivity, and false detection rate to understand the effect of compression on downstream iBMI tasks, specifically, spike detection. We demonstrate that a data CR of 15–265 per channel can be achieved by transmitting address-event pulses for two different biological datasets. The CR further increases to 200– 50K per channel, 50 × more than in prior works, by the selective transmission of event pulses corresponding to neural spikes. A CC of ≈0.9 and spike detection accuracy of over 90% were obtained for the worst-case analysis involving 10K-channel simulated recording and typical analysis using 100 or 384-channel real neural recordings. We also analyzed the collision handling capability for up to 10K channels and observed no significant error, indicating the scalability of the proposed pipeline. We also present initial results to show the ability of intention decoders to work directly on the events generated by the neuromorphic front-end.


An integrated toolbox for creating neuromorphic edge applications

January 2025

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38 Reads

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1 Citation

spiking neural networks (SNNs) and neuromorphic models are believed to be more efficient in general and have more biological realism than the activation functions typically used in deep neural networks, transformer models and generative AI. SNNs have local learning rules, are able to learn on small data sets, and can adapt through neuromodulation. Although research has shown their advantages, there are still few compelling practical applications, especially at the edge where sensors and actuators need to be processed in a timely fashion. One reason for this might be that SNNs are much more challenging to understand, build, and operate due to their intrinsic properties. For instance, the mathematical foundation involves differential equations rather than basic activation functions. To address these challenges, we have developed CARLsim++, an integrated toolbox that facilitates the creation of neuromorphic applications. It extends the highly efficient CARLsim open-source SNN simulator. CARLsim++ encapsulates the mathematical intrinsics and low-level C++ programming by providing a graphical user interface for users to easily create their SNNs and a means to configure sensors and actuators for robotics and other edge devices. These can be accurately simulated before deploying on physical devices. CARLsim++ can lead to rapid development of neuromorphic applications for simulation or edge processing. We introduce CARLsim++ with a closed loop robotic demonstration using neuromorphic computing.


Loss shaping enhances exact gradient learning with Eventprop in spiking neural networks

January 2025

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12 Reads

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8 Citations

Event-based machine learning promises more energy-efficient AI on future neuromorphic hardware. Here, we investigate how the recently discovered Eventprop algorithm for gradient descent on exact gradients in spiking neural networks (SNNs) can be scaled up to challenging keyword recognition benchmarks. We implemented Eventprop in the GPU-enhanced neural networks framework (GeNN) and used it for training recurrent SNNs on the Spiking Heidelberg Digits (SHD) and Spiking Speech Commands (SSC) datasets. We found that learning depended strongly on the loss function and extended Eventprop to a wider class of loss functions to enable effective training. We then tested a large number of data augmentations and regularisations as well as exploring different network structures; and heterogeneous and trainable timescales. We found that when combined with two specific augmentations, the right regularisation and a delay line input, Eventprop networks with one recurrent layer achieved state-of-the-art performance on SHD and good accuracy on SSC. In comparison to a leading surrogate-gradient-based SNN training method, our GeNN Eventprop implementation is 3× faster and uses 4× less memory. This work is a significant step towards a low-power neuromorphic alternative to current machine learning paradigms.


Maximizing information in neuron populations for neuromorphic spike encoding

January 2025

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12 Reads

One of the ways neuromorphic applications emulate the processing performed by the brain is by using spikes as inputs instead of time-varying analog stimuli. Therefore, these time-varying stimuli have to be encoded into spikes, which can induce important information loss. To alleviate this loss, some studies use population coding strategies to encode more information using a population of neurons rather than just one neuron. However, configuring the encoding parameters of such a population is an open research question. This work proposes an approach based on maximizing the mutual information between the signal and the spikes in the population of neurons. The proposed algorithm is inspired by the information-theoretic framework of Partial Information Decomposition. Two applications are presented: blood pressure pulse wave classification, and neural action potential waveform classification. In both tasks, the data is encoded into spikes and the encoding parameters of the neuron populations are tuned to maximize the encoded information using the proposed algorithm. The spikes are then classified and the performance is measured using classification accuracy as a metric. Two key results are reported. First, adding neurons to the population leads to an increase in both mutual information and classification accuracy beyond what could be accounted for by each neuron separately, showing the usefulness of population coding strategies. Second, the classification accuracy obtained with the tuned parameters is near-optimal and it closely follows the mutual information as more neurons are added to the population. Furthermore, the proposed approach significantly outperforms random parameter selection, showing the usefulness of the proposed approach. These results are reproduced in both applications.


Neuromorphic compliant control facilitates human-prosthetic performance for hand grasp functions

January 2025

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2 Reads

Current bionic hands lack the ability of fine force manipulation for grasping fragile objects due to missing human neuromuscular compliance in control. This incompatibility between prosthetic devices and the sensorimotor system has resulted in a high abandonment rate of hand prostheses. To tackle this challenge, we employed a neuromorphic modeling approach, biorealistic control, to regain human-like grasping ability. The biorealistic control restored muscle force regulation and stiffness adaptation using neuromorphic modeling of the neuromuscular reflex units, which was capable of real-time computing of model outputs. We evaluated the dexterity of the biorealistic control with a set of delicate grasp tasks that simulated varying challenging scenarios of grasping fragile objects in daily activities of life, including the Box and Block Task, the Glass Box Task, and the Potato Chip Task. The performance of the biorealistic control was compared with that of proportional control. Results indicated that the biorealistic control with the compliance of the neuromuscular reflex units significantly outperformed the proportional control with more efficient grip forces, higher success rates, fewer break and drop rates. Post-task survey questionnaires revealed that the biorealistic control reduced subjective burdens of task difficulty and improved subjective confidence in control performance significantly. The outcome of the evaluation confirmed that the biorealistic control could achieve superior abilities in fine, accurate, and efficient grasp control for prosthetic users.


Slax: a composable JAX library for rapid and flexible prototyping of spiking neural networks

January 2025

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2 Citations

Spiking Neural Networks (SNNs) offer rich temporal dynamics and unique capabilities, but their training presents challenges. While backpropagation through time (BPTT) with surrogate gradients is the defacto standard for training SNNs, it scales poorly with long time sequences. Alternative learning rules and algorithms could help further develop models and systems across the spectrum of performance, bio-plausibility, and complexity. However, implementing and evaluating these alternatives at scale is cumbersome and error-prone, requiring repeated reimplementations. To address this, we introduce Slax, a JAX-based library designed to accelerate SNN algorithm design and evaluation. Slax is compatible with the broader JAX and Flax ecosystem and provides optimized implementations of diverse training algorithms, enabling direct performance comparisons. Its toolkit includes methods to visualize and debug algorithms through loss landscapes, gradient similarities, and other metrics of model behavior during training. By streamlining the implementation and evaluation of novel SNN learning algorithms, Slax aims to facilitate research and development in this promising field.


Historical perspective and opportunity for computing in memory using floating-gate and resistive non-volatile computing including neuromorphic computing

January 2025

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23 Reads

The effort addresses the research activity around the usage of non-volatile memories (NVM) for storage of ‘weights’ in neural networks and the resulting computation through these memory crossbars. In particular, we focus on the CMOS implementations of, and comparisons between, memristor/resistive random access memory (RRAM) devices, and floating-gate (FG) devices. A historical perspective for illustrating FG and memristor/RRAM devices enables comparison of nonvolatile storage (addressing issues related to resolution, lifetime, endurance etc), feedforward computation (different variants of vector matrix multiplication, tradeoffs between power dissipation and signal to noise ratio etc), programming (addressing issues of selectivity, peripheral circuits, charge trapping etc), and learning algorithms (continuous time LMS or batch update), in these systems. We believe this historical perspective is necessary and timely given the increasing interest in using computation in memory with NVM for a wide variety of memory bound applications.


D-SELD: Dataset-Scalable Exemplar LCA-Decoder

December 2024

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5 Reads

Neuromorphic computing has recently gained significant attention as a promising approach for developing energy-efficient, massively parallel computing systems inspired by the spiking behavior of the human brain and natively mapping spiking neural networks (SNNs). Effective training algorithms for SNNs are imperative for increased adoption of neuromorphic platforms; however, SNN training continues to lag behind advances in other classes of ANN. In this paper, we reduce this gap by proposing an innovative encoder–decoder technique that leverages sparse coding and the locally competitive algorithm (LCA) to provide an algorithm specifically designed for neuromorphic platforms. Using our proposed Dataset-Scalable Exemplar LCA-Decoder we reduce the computational demands and memory requirements associated with training SNNs using error backpropagation methods on increasingly larger training sets. We offer a solution that can be scalably applied to datasets of any size. Our results show the highest reported top-1 test accuracy using SNNs on the ImageNet and CIFAR100 datasets, surpassing previous benchmarks. Specifically, we achieved a record top-1 accuracy of 80.75% on ImageNet (ILSVRC2012 validation set) and 79.32% on CIFAR100 using SNNs.


Continual learning with hebbian plasticity in sparse and predictive coding networks: a survey and perspective

December 2024

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21 Reads

Recently, the use of bio-inspired learning techniques such as Hebbian learning and its closely-related spike-timing-dependent plasticity (STDP) variant have drawn significant attention for the design of compute-efficient AI systems that can continuously learn on-line at the edge. A key differentiating factor regarding this emerging class of neuromorphic continual learning system lies in the fact that learning must be carried using a data stream received in its natural order, as opposed to conventional gradient-based offline training, where a static training dataset is assumed available a priori and randomly shuffled to make the training set independent and identically distributed (i.i.d). In contrast, the emerging class of neuromorphic CL systems covered in this survey must learn to integrate new information on the fly in a non-i.i.d manner, which makes these systems subject to catastrophic forgetting. In order to build the next generation of neuromorphic AI systems that can continuously learn at the edge, a growing number of research groups are studying the use of sparse and predictive Coding (PC)-based Hebbian neural network architectures and the related spiking neural networks (SNNs) equipped with STDP learning. However, since this research field is still emerging, there is a need for providing a holistic view of the different approaches proposed in the literature so far. To this end, this survey covers a number of recent works in the field of neuromorphic CL based on state-of-the-art sparse and PC technology; provides background theory to help interested researchers quickly learn the key concepts; and discusses important future research questions in light of the different works covered in this paper. It is hoped that this survey will contribute towards future research in the field of neuromorphic CL.


(a) The algorithmic latency in frame-based models consists of a buffering latency and a look-ahead latency. The buffering latency matches the frame-shift length (i.e., block size), whereas the look-ahead latency results from the extra look-ahead within a frame, typically used to provide additional processing context to improve performance. (b) A frequency-domain DNN model transforms a noisy audio signal to its T-F representation by the STFT and then fed it into a neural network. (c) Inputs and outputs to the time-domain DNN models are both time-domain signals. (d) Mask-based time-domain DNN models commonly adopt an encoder-separator-decoder architecture.
The proposed DPSNN adopts the encoder-separator-decoder architecture. The encoder uses convolutions to convert waveform signals into 2D feature maps, effectively replacing the function of STFT. In the separator, a 2D mask is calculated, primarily relying on the SCNN and SRNN modules that capture the temporal and frequency contextual information of the encoded feature maps, respectively. After applying the mask to the feature maps from the encoder, the decoder transforms the masked feature maps back to enhanced waveform signals.
(a) In the mask-based encoder-separator-decoder architecture, the encoder converts overlapping frames into 1D features through convolution and aligns them into a 2D feature map. Each 1D feature is processed in one time step in the subsequent spiking layers. (b) In the SCNN layer, a group convolution is applied along the temporal axis of a feature map to capture temporal contextual information. (c) The SRNN layer is a fully-connected recurrent spiking layer that integrates contexts along the frequency direction of its input 2D feature map. (d) Readout is done using a fully-connected layer with non-spiking ALIF neurons, where the membrane potential of these neurons is calculated and output without any spiking or resetting.
Influence of the length of input examples on model performance, as evaluated on the testing set of VCTK. The channels in the model are N=512,B=256,H=512. The frame length ( L) in the encoder is 80. The size of the context steps in SCNN is 4.
Performance of the SDNN baseline model [12] across varying frame lengths. The model was trained using different frame lengths (8 ms, 16 ms, and 32 ms) and then evaluated on the Intel N-DNS Challenge dataset. We observe that the frame length significantly influences both SI-SNR and DNSMOS OVRL.
DPSNN: spiking neural network for low-latency streaming speech enhancement

December 2024

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34 Reads

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1 Citation

Speech enhancement improves communication in noisy environments, affecting areas such as automatic speech recognition (ASR), hearing aids, and telecommunications. With these domains typically being power-constrained and event-based, and often requiring low latency, neuromorphic algorithms–particularly spiking neural networks (SNNs)–hold significant potential. However, current effective SNN solutions require a long temporal window to calculate Short Time Fourier Transforms (STFTs) and thus impose substantial latency, typically around 32 ms, which is too long for applications such as hearing aids. Inspired by the Dual-Path Recurrent Neural Network (DPRNN) in deep neural networks (DNNs), we develop a two-phase time-domain streaming SNN fframework for speech enhancement, named Dual-Path Spiking Neural Network (DPSNN). DPSNNs achieve low latency by replacing the STFT and inverse STFT (iSTFT) in traditional frequency-domain models with a learned convolutional encoder and decoder. In the DPSNN, the first phase uses Spiking Convolutional Neural Networks (SCNNs) to capture temporal contextual information, while the second phase uses Spiking Recurrent Neural Networks (SRNNs) to focus on frequency-related features. In addition, threshold-based activation suppression, along with L1 regularization loss, is applied to specific non-spiking layers in DPSNNs to further improve their energy efficiency. Evaluating on the Voice Cloning Toolkit (VCTK) Corpus and Intel N-DNS Challenge dataset, our approach demonstrates excellent performance in speech objective metrics, along with the very low latency (approximately 5 ms) required for applications like hearing aids.



Self-reconfigurable multifunctional memristive nociceptor for intelligent robotics

November 2024

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35 Reads

Artificial nociceptors, mimicking human-like stimuli perception, are of significance for intelligent robotics to work in hazardous and dynamic scenarios. One of the most essential characteristics of the human nociceptor is its self-adjustable attribute, which indicates that the threshold of determination of a potentially hazardous stimulus relies on environmental knowledge. This critical attribute has been currently omitted, but it is highly desired for artificial nociceptors. Inspired by these shortcomings, this article presents, for the first time, a self-directed channel memristor-based self-reconfigurable nociceptor, capable of perceiving hazardous pressure stimuli under different temperatures and demonstrates key features of tactile nociceptors, including ‘threshold,’ ‘no-adaptation,’ and ‘sensitization.’ The maximum amplification of hazardous external stimuli is 1000%, and its response characteristics dynamically adapt to current temperature conditions by automatically altering the generated modulation schemes for the memristor. The maximum difference ratio of the response of memristors at different temperatures is 500%, and this adaptability closely mimics the functions of biological tactile nociceptors, resulting in accurate danger perception in various conditions. Beyond temperature adaptation, this memristor-based nociceptor has the potential to integrate different sensory modalities by applying various sensors, thereby achieving human-like perception capabilities in real-world environments.


Journal metrics


5.8 (2023)

Journal Impact Factor™


69%

Acceptance rate


5.9 (2023)

CiteScore™


9 days

Submission to first decision


98 days

Submission to publication


1.1 (2023)

Immediacy Index


1.366 (2023)

SJR


£2,000 / € 2,300 / $2,700

Article processing charge

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