35 research outputs found
Beyond LIF neurons on neuromorphic hardware
Neuromorphic systems aim to provide accelerated low-power simulation of Spiking Neural Networks (SNNs), typically featuring simple and efficient neuron models such as the Leaky Integrate-and-Fire (LIF) model. Biologically plausible neuron models developed by neuroscientists are largely ignored in neuromorphic computing due to their increased computational costs. This work bridges this gap through implementation and evaluation of a single compartment Hodgkin-Huxley (HH) neuron and a multi-compartment neuron incorporating dendritic computation on the SpiNNaker, and SpiNNaker2 prototype neuromorphic systems. Numerical accuracy of the model implementations is benchmarked against reference models in the NEURON simulation environment, with excellent agreement achieved by both the fixed- and floating-point SpiNNaker implementations. The computational cost is evaluated in terms of timing measurements profiling neural state updates. While the additional model complexity understandably increases computation times relative to LIF models, it was found a wallclock time increase of only 8× was observed for the HH neuron (11× for the mutlicompartment model), demonstrating the potential of hardware accelerators in the next-generation neuromorphic system to optimize implementation of complex neuron models. The benefits of models directly corresponding to biophysiological data are demonstrated: HH neurons are able to express a range of output behaviors not captured by LIF neurons; and the dendritic compartment provides the first implementation of a spiking multi-compartment neuron model with XOR-solving capabilities on neuromorphic hardware. The work paves the way for inclusion of more biologically representative neuron models in neuromorphic systems, and showcases the benefits of hardware accelerators included in the next-generation SpiNNaker2 architecture
Spatiotemporal Spike-Pattern Selectivity in Single Mixed-Signal Neurons with Balanced Synapses
Realizing the potential of mixed-signal neuromorphic processors for
ultra-low-power inference and learning requires efficient use of their
inhomogeneous analog circuitry as well as sparse, time-based information
encoding and processing. Here, we investigate spike-timing-based spatiotemporal
receptive fields of output-neurons in the Spatiotemporal Correlator (STC)
network, for which we used excitatory-inhibitory balanced disynaptic inputs
instead of dedicated axonal or neuronal delays. We present hardware-in-the-loop
experiments with a mixed-signal DYNAP-SE neuromorphic processor, in which
five-dimensional receptive fields of hardware neurons were mapped by randomly
sampling input spike-patterns from a uniform distribution. We find that, when
the balanced disynaptic elements are randomly programmed, some of the neurons
display distinct receptive fields. Furthermore, we demonstrate how a neuron was
tuned to detect a particular spatiotemporal feature, to which it initially was
non-selective, by activating a different subset of the inhomogeneous analog
synaptic circuits. The energy dissipation of the balanced synaptic elements is
one order of magnitude lower per lateral connection (0.65 nJ vs 9.3 nJ per
spike) than former delay-based neuromorphic hardware implementations. Thus, we
show how the inhomogeneous synaptic circuits could be utilized for
resource-efficient implementation of STC network layers, in a way that enables
synapse-address reprogramming as a discrete mechanism for feature tuning.Comment: This work has been submitted to the IEEE for possible publication.
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Versatile emulation of spiking neural networks on an accelerated neuromorphic substrate
We present first experimental results on the novel BrainScaleS-2 neuromorphic
architecture based on an analog neuro-synaptic core and augmented by embedded
microprocessors for complex plasticity and experiment control. The high
acceleration factor of 1000 compared to biological dynamics enables the
execution of computationally expensive tasks, by allowing the fast emulation of
long-duration experiments or rapid iteration over many consecutive trials. The
flexibility of our architecture is demonstrated in a suite of five distinct
experiments, which emphasize different aspects of the BrainScaleS-2 system
Emulating insect brains for neuromorphic navigation
Bees display the remarkable ability to return home in a straight line after
meandering excursions to their environment. Neurobiological imaging studies
have revealed that this capability emerges from a path integration mechanism
implemented within the insect's brain. In the present work, we emulate this
neural network on the neuromorphic mixed-signal processor BrainScaleS-2 to
guide bees, virtually embodied on a digital co-processor, back to their home
location after randomly exploring their environment. To realize the underlying
neural integrators, we introduce single-neuron spike-based short-term memory
cells with axo-axonic synapses. All entities, including environment, sensory
organs, brain, actuators, and the virtual body, run autonomously on a single
BrainScaleS-2 microchip. The functioning network is fine-tuned for better
precision and reliability through an evolution strategy. As BrainScaleS-2
emulates neural processes 1000 times faster than biology, 4800 consecutive bee
journeys distributed over 320 generations occur within only half an hour on a
single neuromorphic core
Modeling and Verification for a Scalable Neuromorphic Substrate
Mixed-signal accelerated neuromorphic hardware is a class of devices that implements physical models of neural networks in dedicated analog and digital circuits. These devices offer the advantages of high acceleration and energy efficiency for the emulation of spiking neural networks but pose constraints in form of device variability and of limited connectivity and bandwidth. We address these constraints using two complementary approaches: At the network level, the influence of multiple distortion mechanisms on two benchmark models is analyzed and compensation methods are developed that counteract the resulting effects. The compensation methods are validated using a simulation of the BrainScaleS neuromorphic hardware system. At the single neuron level, calibration procedures are presented that counteract device variability for a new analog implementation of an adaptive exponential integrate-and-fire neuron model in a 65 nm process. The functionality of the neuron circuit together with these calibration methods is verified in detailed transistor-level simulations before production. The versatility of the circuit design that includes novel multi-compartment and plateau-potential features is demonstrated in use cases inspired by biology and machine learning
Full Wafer Redistribution and Wafer Embedding as Key Technologies for a Multi-Scale Neuromorphic Hardware Cluster
Together with the Kirchhoff-Institute for Physics(KIP) the Fraunhofer IZM has
developed a full wafer redistribution and embedding technology as base for a
large-scale neuromorphic hardware system. The paper will give an overview of
the neuromorphic computing platform at the KIP and the associated hardware
requirements which drove the described technological developments. In the first
phase of the project standard redistribution technologies from wafer level
packaging were adapted to enable a high density reticle-to-reticle routing on
200mm CMOS wafers. Neighboring reticles were interconnected across the scribe
lines with an 8{\mu}m pitch routing based on semi-additive copper
metallization. Passivation by photo sensitive benzocyclobutene was used to
enable a second intra-reticle routing layer. Final IO pads with flash gold were
generated on top of each reticle. With that concept neuromorphic systems based
on full wafers could be assembled and tested. The fabricated high density
inter-reticle routing revealed a very high yield of larger than 99.9%. In order
to allow an upscaling of the system size to a large number of wafers with
feasible effort a full wafer embedding concept for printed circuit boards was
developed and proven in the second phase of the project. The wafers were
thinned to 250{\mu}m and laminated with additional prepreg layers and copper
foils into a core material. After lamination of the PCB panel the reticle IOs
of the embedded wafer were accessed by micro via drilling, copper
electroplating, lithography and subtractive etching of the PCB wiring
structure. The created wiring with 50um line width enabled an access of the
reticle IOs on the embedded wafer as well as a board level routing. The panels
with the embedded wafers were subsequently stressed with up to 1000 thermal
cycles between 0C and 100C and have shown no severe failure formation over the
cycle time.Comment: Accepted at EPTC 201
Neuromorphic Electronic Circuits for Building Autonomous Cognitive Systems
Chicca E, Stefanini F, Bartolozzi C, Indiveri G. Neuromorphic Electronic Circuits for Building Autonomous Cognitive Systems. In: Proceedings of the IEEE. Proceedings of the IEEE. Vol 102. Piscataway, NJ: IEEE; 2014: 1367-1388.Several analog and digital brain-inspired electronic systems have been recently proposed as dedicated solutions for fast simulations of spiking neural networks. While these architectures are useful for exploring the computational properties of large-scale models of the nervous system, the challenge of building low-power compact physical artifacts that can behave intelligently in the real world and exhibit cognitive abilities still remains open. In this paper, we propose a set of neuromorphic engineering solutions to address this challenge. In particular, we review neuromorphic circuits for emulating neural and synaptic dynamics in real time and discuss the role of biophysically realistic temporal dynamics in hardware neural processing architectures; we review the challenges of realizing spike-based plasticity mechanisms in real physical systems and present examples of analog electronic circuits that implement them; we describe the computational properties of recurrent neural networks and show how neuromorphic winner-take-all circuits can implement working-memory and decision-making mechanisms. We validate the neuromorphic approach proposed with experimental results obtained from our own circuits and systems, and argue how the circuits and networks presented in this work represent a useful set of components for efficiently and elegantly implementing neuromorphic cognition