尖峰神经网络（SNN）是大脑中低功率，耐断层的信息处理的基础，并且在适当的神经形态硬件加速器上实施时，可能构成传统深层神经网络的能力替代品。但是，实例化解决复杂的计算任务的SNN在Silico中仍然是一个重大挑战。替代梯度（SG）技术已成为培训SNN端到端的标准解决方案。尽管如此，它们的成功取决于突触重量初始化，类似于常规的人工神经网络（ANN）。然而，与ANN不同，它仍然难以捉摸地构成SNN的良好初始状态。在这里，我们为受到大脑中通常观察到的波动驱动的策略启发的SNN制定了一般初始化策略。具体而言，我们为数据依赖性权重初始化提供了实用的解决方案，以确保广泛使用的泄漏的集成和传火（LIF）神经元的波动驱动。我们从经验上表明，经过SGS培训时，SNN遵循我们的策略表现出卓越的学习表现。这些发现概括了几个数据集和SNN体系结构，包括完全连接，深度卷积，经常性和更具生物学上合理的SNN遵守Dale的定律。因此，波动驱动的初始化提供了一种实用，多功能且易于实现的策略，可改善神经形态工程和计算神经科学的不同任务的SNN培训绩效。

穗状花序的神经形状硬件占据了深度神经网络（DNN）的更节能实现的承诺，而不是GPU的标准硬件。但这需要了解如何在基于事件的稀疏触发制度中仿真DNN，否则能量优势丢失。特别地，解决序列处理任务的DNN通常采用难以使用少量尖峰效仿的长短期存储器（LSTM）单元。我们展示了许多生物神经元的面部，在每个尖峰后缓慢的超积极性（AHP）电流，提供了有效的解决方案。 AHP电流可以轻松地在支持多舱神经元模型的神经形状硬件中实现，例如英特尔的Loihi芯片。滤波近似理论解释为什么AHP-Neurons可以模拟LSTM单元的功能。这产生了高度节能的时间序列分类方法。此外，它为实现了非常稀疏的大量大型DNN来实现基础，这些大型DNN在文本中提取单词和句子之间的关系，以便回答有关文本的问题。

Spiking neural networks (SNN) are a viable alternative to conventional artificial neural networks when energy efficiency and computational complexity are of importance. A major advantage of SNNs is their binary information transfer through spike trains. The training of SNN has, however, been a challenge, since neuron models are non-differentiable and traditional gradient-based backpropagation algorithms cannot be applied directly. Furthermore, spike-timing-dependent plasticity (STDP), albeit being a spike-based learning rule, updates weights locally and does not optimize for the output error of the network. We present desire backpropagation, a method to derive the desired spike activity of neurons from the output error. The loss function can then be evaluated locally for every neuron. Incorporating the desire values into the STDP weight update leads to global error minimization and increasing classification accuracy. At the same time, the neuron dynamics and computational efficiency of STDP are maintained, making it a spike-based supervised learning rule. We trained three-layer networks to classify MNIST and Fashion-MNIST images and reached an accuracy of 98.41% and 87.56%, respectively. Furthermore, we show that desire backpropagation is computationally less complex than backpropagation in traditional neural networks.

由于它们的低能量消耗，对神经形态计算设备上的尖刺神经网络（SNNS）越来越兴趣。最近的进展使培训SNNS在精度方面开始与传统人工神经网络（ANNS）进行竞争，同时在神经胸壁上运行时的节能。然而，培训SNNS的过程仍然基于最初为ANNS开发的密集的张量操作，这不利用SNN的时空稀疏性质。我们在这里介绍第一稀疏SNN BackPropagation算法，该算法与最新的现有技术实现相同或更好的准确性，同时显着更快，更高的记忆力。我们展示了我们对不同复杂性（时尚 - MNIST，神经影像学 - MNIST和Spiking Heidelberg数字的真实数据集的有效性，在不失精度的情况下实现了高达150倍的后向通行证的加速，而不会减少精度。

过去十年来，人们对人工智能（AI）的兴趣激增几乎完全由人工神经网络（ANN）的进步驱动。尽管ANN为许多以前棘手的问题设定了最先进的绩效，但它们需要大量的数据和计算资源进行培训，并且由于他们采用了监督的学习，他们通常需要知道每个培训示例的正确标记的响应，并限制它们对现实世界域的可扩展性。尖峰神经网络（SNN）是使用更多类似脑部神经元的ANN的替代方法，可以使用无监督的学习来发现输入数据中的可识别功能，而又不知道正确的响应。但是，SNN在动态稳定性方面挣扎，无法匹配ANN的准确性。在这里，我们展示了SNN如何克服文献中发现的许多缺点，包括为消失的尖峰问题提供原则性解决方案，以优于所有现有的浅SNN，并等于ANN的性能。它在使用无标记的数据和仅1/50的训练时期使用无监督的学习时完成了这一点（标记数据仅用于最终的简单线性读数层）。该结果使SNN成为可行的新方法，用于使用未标记的数据集快速，准确，有效，可解释的机器学习。

We propose a novel backpropagation algorithm for training spiking neural networks (SNNs) that encodes information in the relative multiple spike timing of individual neurons without single-spike restrictions. The proposed algorithm inherits the advantages of conventional timing-based methods in that it computes accurate gradients with respect to spike timing, which promotes ideal temporal coding. Unlike conventional methods where each neuron fires at most once, the proposed algorithm allows each neuron to fire multiple times. This extension naturally improves the computational capacity of SNNs. Our SNN model outperformed comparable SNN models and achieved as high accuracy as non-convolutional artificial neural networks. The spike count property of our networks was altered depending on the time constant of the postsynaptic current and the membrane potential. Moreover, we found that there existed the optimal time constant with the maximum test accuracy. That was not seen in conventional SNNs with single-spike restrictions on time-to-fast-spike (TTFS) coding. This result demonstrates the computational properties of SNNs that biologically encode information into the multi-spike timing of individual neurons. Our code would be publicly available.

In a recent paper Wunderlich and Pehle introduced the EventProp algorithm that enables training spiking neural networks by gradient descent on exact gradients. In this paper we present extensions of EventProp to support a wider class of loss functions and an implementation in the GPU enhanced neuronal networks framework which exploits sparsity. The GPU acceleration allows us to test EventProp extensively on more challenging learning benchmarks. We find that EventProp performs well on some tasks but for others there are issues where learning is slow or fails entirely. Here, we analyse these issues in detail and discover that they relate to the use of the exact gradient of the loss function, which by its nature does not provide information about loss changes due to spike creation or spike deletion. Depending on the details of the task and loss function, descending the exact gradient with EventProp can lead to the deletion of important spikes and so to an inadvertent increase of the loss and decrease of classification accuracy and hence a failure to learn. In other situations the lack of knowledge about the benefits of creating additional spikes can lead to a lack of gradient flow into earlier layers, slowing down learning. We eventually present a first glimpse of a solution to these problems in the form of `loss shaping', where we introduce a suitable weighting function into an integral loss to increase gradient flow from the output layer towards earlier layers.

这项研究提出了依赖电压突触可塑性（VDSP），这是一种新型的脑启发的无监督的本地学习规则，用于在线实施HEBB对神经形态硬件的可塑性机制。拟议的VDSP学习规则仅更新了突触后神经元的尖峰的突触电导，这使得相对于标准峰值依赖性可塑性（STDP）的更新数量减少了两倍。此更新取决于突触前神经元的膜电位，该神经元很容易作为神经元实现的一部分，因此不需要额外的存储器来存储。此外，该更新还对突触重量进行了正规化，并防止重复刺激时的重量爆炸或消失。进行严格的数学分析以在VDSP和STDP之间达到等效性。为了验证VDSP的系统级性能，我们训练一个单层尖峰神经网络（SNN），以识别手写数字。我们报告85.01 $ \ pm $ 0.76％（平均$ \ pm $ s.d。）对于MNIST数据集中的100个输出神经元网络的精度。在缩放网络大小时，性能会提高（400个输出神经元的89.93 $ \ pm $ 0.41％，500个神经元为90.56 $ \ pm $ 0.27），这验证了大规模计算机视觉任务的拟议学习规则的适用性。有趣的是，学习规则比STDP更好地适应输入信号的频率，并且不需要对超参数进行手动调整。

Event-based simulations of Spiking Neural Networks (SNNs) are fast and accurate. However, they are rarely used in the context of event-based gradient descent because their implementations on GPUs are difficult. Discretization with the forward Euler method is instead often used with gradient descent techniques but has the disadvantage of being computationally expensive. Moreover, the lack of precision of discretized simulations can create mismatches between the simulated models and analog neuromorphic hardware. In this work, we propose a new exact error-backpropagation through spikes method for SNNs, extending Fast \& Deep to multiple spikes per neuron. We show that our method can be efficiently implemented on GPUs in a fully event-based manner, making it fast to compute and precise enough for analog neuromorphic hardware. Compared to the original Fast \& Deep and the current state-of-the-art event-based gradient-descent algorithms, we demonstrate increased performance on several benchmark datasets with both feedforward and convolutional SNNs. In particular, we show that multi-spike SNNs can have advantages over single-spike networks in terms of convergence, sparsity, classification latency and sensitivity to the dead neuron problem.

由于它们的时间加工能力及其低交换（尺寸，重量和功率）以及神经形态硬件中的节能实现，尖峰神经网络（SNNS）已成为传统人工神经网络（ANN）的有趣替代方案。然而，培训SNNS所涉及的挑战在准确性方面有限制了它们的表现，从而限制了他们的应用。因此，改善更准确的特征提取的学习算法和神经架构是SNN研究中的当前优先级之一。在本文中，我们展示了现代尖峰架构的关键组成部分的研究。我们在从最佳执行网络中凭经验比较了图像分类数据集中的不同技术。我们设计了成功的残余网络（Reset）架构的尖峰版本，并测试了不同的组件和培训策略。我们的结果提供了SNN设计的最新版本，它允许在尝试构建最佳视觉特征提取器时进行明智的选择。最后，我们的网络优于CIFAR-10（94.1％）和CIFAR-100（74.5％）数据集的先前SNN架构，并将现有技术与DVS-CIFAR10（71.3％）相匹配，参数较少而不是先前的状态艺术，无需安静转换。代码在https://github.com/vicenteax/spiking_resnet上获得。

Spiking neural networks (SNNs) are promising brain-inspired energy-efficient models. Recent progress in training methods has enabled successful deep SNNs on large-scale tasks with low latency. Particularly, backpropagation through time (BPTT) with surrogate gradients (SG) is popularly used to achieve high performance in a very small number of time steps. However, it is at the cost of large memory consumption for training, lack of theoretical clarity for optimization, and inconsistency with the online property of biological learning and rules on neuromorphic hardware. Other works connect spike representations of SNNs with equivalent artificial neural network formulation and train SNNs by gradients from equivalent mappings to ensure descent directions. But they fail to achieve low latency and are also not online. In this work, we propose online training through time (OTTT) for SNNs, which is derived from BPTT to enable forward-in-time learning by tracking presynaptic activities and leveraging instantaneous loss and gradients. Meanwhile, we theoretically analyze and prove that gradients of OTTT can provide a similar descent direction for optimization as gradients based on spike representations under both feedforward and recurrent conditions. OTTT only requires constant training memory costs agnostic to time steps, avoiding the significant memory costs of BPTT for GPU training. Furthermore, the update rule of OTTT is in the form of three-factor Hebbian learning, which could pave a path for online on-chip learning. With OTTT, it is the first time that two mainstream supervised SNN training methods, BPTT with SG and spike representation-based training, are connected, and meanwhile in a biologically plausible form. Experiments on CIFAR-10, CIFAR-100, ImageNet, and CIFAR10-DVS demonstrate the superior performance of our method on large-scale static and neuromorphic datasets in small time steps.

Models of sensory processing and learning in the cortex need to efficiently assign credit to synapses in all areas. In deep learning, a known solution is error backpropagation, which however requires biologically implausible weight transport from feed-forward to feedback paths. We introduce Phaseless Alignment Learning (PAL), a bio-plausible method to learn efficient feedback weights in layered cortical hierarchies. This is achieved by exploiting the noise naturally found in biophysical systems as an additional carrier of information. In our dynamical system, all weights are learned simultaneously with always-on plasticity and using only information locally available to the synapses. Our method is completely phase-free (no forward and backward passes or phased learning) and allows for efficient error propagation across multi-layer cortical hierarchies, while maintaining biologically plausible signal transport and learning. Our method is applicable to a wide class of models and improves on previously known biologically plausible ways of credit assignment: compared to random synaptic feedback, it can solve complex tasks with less neurons and learn more useful latent representations. We demonstrate this on various classification tasks using a cortical microcircuit model with prospective coding.

错误 - 背面范围（BackProp）算法仍然是人工神经网络中信用分配问题的最常见解决方案。在神经科学中，尚不清楚大脑是否可以采用类似的策略来纠正其突触。最近的模型试图弥合这一差距，同时与一系列实验观察一致。但是，这些模型要么无法有效地跨多层返回误差信号，要么需要多相学习过程，它们都不让人想起大脑中的学习。在这里，我们介绍了一种新模型，破裂的皮质皮质网络（BUSTCCN），该网络通过整合了皮质网络的已知特性，即爆发活动，短期可塑性（STP）和dendrite-target-targeting Interneurons来解决这些问题。 BUSTCCN依赖于连接型特异性STP的突发多路复用来传播深层皮质网络中的反向Prop样误差信号。这些误差信号是在远端树突上编码的，由于兴奋性抑制性抑制性倒入输入而诱导爆发依赖性可塑性。首先，我们证明我们的模型可以使用单相学习过程有效地通过多层回溯错误。接下来，我们通过经验和分析表明，在我们的模型中学习近似反向推广的梯度。最后，我们证明我们的模型能够学习复杂的图像分类任务（MNIST和CIFAR-10）。总体而言，我们的结果表明，跨细胞，细胞，微电路和系统水平的皮质特征共同基于大脑中的单相有效深度学习。

由于稀疏，异步和二进制事件（或尖峰）驱动加工，尖峰神经网络（SNNS）最近成为深度学习的替代方案，可以在神经形状硬件上产生巨大的能效益。然而，从划痕训练高精度和低潜伏期的SNN，患有尖刺神经元的非微弱性质。要在SNNS中解决此培训问题，我们重新批准批量标准化，并通过时间（BNTT）技术提出时间批量标准化。大多数先前的SNN工程到现在忽略了批量标准化，认为它无效地训练时间SNN。与以前的作品不同，我们提出的BNTT沿着时轴沿着时间轴解耦的参数，以捕获尖峰的时间动态。在BNTT中的时间上不断发展的可学习参数允许神经元通过不同的时间步长来控制其尖峰率，从头开始实现低延迟和低能量训练。我们对CiFar-10，CiFar-100，微小想象特和事件驱动的DVS-CIFAR10数据集进行实验。 BNTT允许我们首次在三个复杂的数据集中培训深度SNN架构，只需25-30步即可。我们还使用BNTT中的参数分布提前退出算法，以降低推断的延迟，进一步提高了能量效率。

The term ``neuromorphic'' refers to systems that are closely resembling the architecture and/or the dynamics of biological neural networks. Typical examples are novel computer chips designed to mimic the architecture of a biological brain, or sensors that get inspiration from, e.g., the visual or olfactory systems in insects and mammals to acquire information about the environment. This approach is not without ambition as it promises to enable engineered devices able to reproduce the level of performance observed in biological organisms -- the main immediate advantage being the efficient use of scarce resources, which translates into low power requirements. The emphasis on low power and energy efficiency of neuromorphic devices is a perfect match for space applications. Spacecraft -- especially miniaturized ones -- have strict energy constraints as they need to operate in an environment which is scarce with resources and extremely hostile. In this work we present an overview of early attempts made to study a neuromorphic approach in a space context at the European Space Agency's (ESA) Advanced Concepts Team (ACT).

最近的研究表明，卷积神经网络（CNNS）不是图像分类的唯一可行的解决方案。此外，CNN中使用的重量共享和反向验证不对应于预测灵长类动物视觉系统中存在的机制。为了提出更加生物合理的解决方案，我们设计了使用峰值定时依赖性塑性（STDP）和其奖励调制变体（R-STDP）学习规则训练的本地连接的尖峰神经网络（SNN）。使用尖刺神经元和局部连接以及强化学习（RL）将我们带到了所提出的架构中的命名法生物网络。我们的网络由速率编码的输入层组成，后跟局部连接的隐藏层和解码输出层。采用尖峰群体的投票方案进行解码。我们使用Mnist DataSet获取图像分类准确性，并评估我们有益于于不同目标响应的奖励系统的稳健性。

我们训练神经形态硬件芯片以通过变分能最小化近似Quantum旋转模型的地面状态。与使用马尔可夫链蒙特卡罗进行样品生成的变分人工神经网络相比，这种方法具有优点：神经形态器件以快速和固有的并行方式产生样品。我们开发培训算法，并将其应用于横向场介绍模型，在中等系统尺寸下显示出良好的性能（$ n \ LEQ 10 $）。系统的普遍开心研究表明，较大系统尺寸的可扩展性主要取决于样品质量，该样品质量受到模拟神经芯片上的参数漂移的限制。学习性能显示阈值行为作为ansatz的变分参数的数量的函数，大约为50美元的隐藏神经元，足以表示关键地位，最高$ n = 10 $。网络参数的6 + 1位分辨率不会限制当前设置中的可达近似质量。我们的工作为利用神经形态硬件的能力提供了一种重要的一步，以解决量子数量问题中的维数诅咒。

复发性神经网络（RNN）的可伸缩性受到每个时间步骤计算对先前时间步长输出的顺序依赖性的阻碍。因此，加快和扩展RNN的一种方法是减少每个时间步长所需的计算，而不是模型大小和任务。在本文中，我们提出了一个模型，该模型将封闭式复发单元（GRU）作为基于事件的活动模型，我们称为基于事件的GRU（EGRU），其中仅在收到输入事件（事件 - 基于其他单位。当与一次活跃的单位仅一小部分（活动 - 帕斯斯）相结合时，该模型具有比当前RNN的计算更高效的潜力。值得注意的是，我们模型中的活动 - 表格性也转化为梯度下降期间稀疏参数更新，从而将此计算效率扩展到训练阶段。我们表明，与现实世界中最新的经常性网络模型相比，EGRU表现出竞争性能，包括语言建模，同时在推理和培训期间自然保持高活动稀疏性。这为下一代重复网络奠定了基础，这些网络可扩展，更适合新型神经形态硬件。

我们提出了Memprop，即采用基于梯度的学习来培训完全的申请尖峰神经网络（MSNNS）。我们的方法利用固有的设备动力学来触发自然产生的电压尖峰。这些由回忆动力学发出的尖峰本质上是类似物，因此完全可区分，这消除了尖峰神经网络（SNN）文献中普遍存在的替代梯度方法的需求。回忆性神经网络通常将备忘录集成为映射离线培训网络的突触，或者以其他方式依靠关联学习机制来训练候选神经元的网络。相反，我们直接在循环神经元和突触的模拟香料模型上应用了通过时间（BPTT）训练算法的反向传播。我们的实现是完全的综合性，因为突触重量和尖峰神经元都集成在电阻RAM（RRAM）阵列上，而无需其他电路来实现尖峰动态，例如模数转换器（ADCS）或阈值比较器。结果，高阶电物理效应被充分利用，以在运行时使用磁性神经元的状态驱动动力学。通过朝着非同一梯度的学习迈进，我们在以前报道的几个基准上的轻巧密集的完全MSNN中获得了高度竞争的准确性。

大脑中尖刺神经元之间的沟通的事件驱动和稀疏性质对灵活和节能的AI来说具有很大的承诺。学习算法的最新进展已经证明，与标准经常性神经网络相比，可以有效地培训尖刺神经元的复发网络以实现竞争性能。尽管如此，随着这些学习算法使用错误 - 反复通过时间（BPTT），它们遭受了高的内存要求，慢慢训练，并且与在线学习不兼容。这将这些学习算法的应用限制为相对较小的网络和有限的时间序列长度。已经提出了具有较低计算和内存复杂性的BPTT的在线近似（E-PROP，OSTL），但在实践中也遭受内存限制，并且作为近似，不要倾销标准BPTT训练。在这里，我们展示了最近开发的BPTT替代方法，通过时间（FPTT）可以应用于尖峰神经网络。与BPTT不同，FPTT试图最大限度地减少损失的持续动态正常风险。结果，可以以在线方式计算FPTT，并且相对于序列长度具有固定的复杂性。与新型动态尖刺神经元模型结合时，液态常数神经元，我们表明SNNS培训了FPTT优于在线BPTT近似，并在时间分类任务上接近或超过离线BPTT精度。因此，这种方法使得在长期序列中以记忆友好的在线方式训练SNNS并向新颖和复杂的神经架构进行扩展。