221 research outputs found
Optimization and parallelization of tensor and ODE/PDE computations on GPU
We propose a multi-level GPU-based parallelization algorithm to solve the multi-compartment
Hodgkin Huxley (HH) model equation that requires solving the Hines matrix. We use
a ‘parallel-in-time’ algorithm (like the Parareal strategy) for obtaining outer level parallelism,
and an Exact Domain Decomposition (EDD) algorithm with fine-decomposition for
inner-level parallelism. We show that our technique can also be applied to any differential
equation like the heat equations which induce tridiagonal systems.
Typically, a solution to the HH equation runs for hundreds to tens of thousands of time-steps
while solving a Hines matrix at each time step. Previous solutions by Michael Mascagni
et al. (1991) and Hines et al. (2008) to this problem have tackled only solving the Hines
matrix in parallel.
Our approach uses the dynamic parallelism of CUDA to achieve multi-level parallelism
on GPUs. Our solution outperforms the sequential time method on standard neuron morphologies
upto 2.5x. We also show that iterative part of parareal method converges in 5-7
iterations on average with an accuracy of 10−6.
We also propose a GPU optimization for the Higher Order Tensor Renormalization Group
problem, where the tensor contraction operations inside HOTRG is optimized by a multi-
GPU implementation using cuBLAS xt API
Simulation of networks of spiking neurons: A review of tools and strategies
We review different aspects of the simulation of spiking neural networks. We
start by reviewing the different types of simulation strategies and algorithms
that are currently implemented. We next review the precision of those
simulation strategies, in particular in cases where plasticity depends on the
exact timing of the spikes. We overview different simulators and simulation
environments presently available (restricted to those freely available, open
source and documented). For each simulation tool, its advantages and pitfalls
are reviewed, with an aim to allow the reader to identify which simulator is
appropriate for a given task. Finally, we provide a series of benchmark
simulations of different types of networks of spiking neurons, including
Hodgkin-Huxley type, integrate-and-fire models, interacting with current-based
or conductance-based synapses, using clock-driven or event-driven integration
strategies. The same set of models are implemented on the different simulators,
and the codes are made available. The ultimate goal of this review is to
provide a resource to facilitate identifying the appropriate integration
strategy and simulation tool to use for a given modeling problem related to
spiking neural networks.Comment: 49 pages, 24 figures, 1 table; review article, Journal of
Computational Neuroscience, in press (2007
Computational convergence of the path integral for real dendritic morphologies
Neurons are characterised by a morphological structure unique amongst biological cells, the core of which is the dendritic tree. The vast number of dendritic geometries, combined with heterogeneous properties of the cell membrane, continue to challenge scientists in predicting neuronal input-output relationships, even in the case of sub-threshold dendritic currents. The Green’s function obtained for a given dendritic geometry provides this functional relationship for passive or quasi-active dendrites and can be constructed by a sum-over-trips approach based on a path integral formalism. In this paper, we introduce a number of efficient algorithms for realisation of the sum-over-trips framework and investigate the convergence of these algorithms on different dendritic geometries. We demonstrate that the convergence of the trip sampling methods strongly depends on dendritic morphology as well as the biophysical properties of the cell membrane. For real morphologies, the number of trips to guarantee a small convergence error might become very large and strongly affect computational efficiency. As an alternative, we introduce a highly-efficient matrix method which can be applied to arbitrary branching structures
Design and evaluation of tridiagonal solvers for vector and parallel computers
Postprint (published version
Statistical physics of neural systems with non-additive dendritic coupling
How neurons process their inputs crucially determines the dynamics of
biological and artificial neural networks. In such neural and neural-like
systems, synaptic input is typically considered to be merely transmitted
linearly or sublinearly by the dendritic compartments. Yet, single-neuron
experiments report pronounced supralinear dendritic summation of sufficiently
synchronous and spatially close-by inputs. Here, we provide a statistical
physics approach to study the impact of such non-additive dendritic processing
on single neuron responses and the performance of associative memory tasks in
artificial neural networks. First, we compute the effect of random input to a
neuron incorporating nonlinear dendrites. This approach is independent of the
details of the neuronal dynamics. Second, we use those results to study the
impact of dendritic nonlinearities on the network dynamics in a paradigmatic
model for associative memory, both numerically and analytically. We find that
dendritic nonlinearities maintain network convergence and increase the
robustness of memory performance against noise. Interestingly, an intermediate
number of dendritic branches is optimal for memory functionality
The effect of noise in models of spiny dendrites
The dendritic tree provides the surface area for synaptic connections between the
100 billion neurons in the brain. 90% of excitatory synapses are made onto dendritic
spines which are constantly changing shape and strength. This adaptation is believed
to be an important factor in learning, memory and computations within the dendritic
tree. The environment in which the neuron sits is inherently noisy due to the activity
in nearby neurons and the stochastic nature of synaptic gating. Therefore the effects
of noise is a very important aspect in any realistic model.
This work provides a comprehensive study of two spiny dendrite models driven
by different forms of noise in the spine dynamics or in the membrane voltage. We
investigate the effect of the noise on signal propagation along the dendrite and how
any correlation in the noise may affect this behaviour. We discover a difference in
the results of the two models which suggests that the form of spine connectivity is
important. We also show that both models have the capacity to act as a robust filter
and that a branched structure can perform logic computations
Dynamics of spatially extended dendrites
Dendrites are the most visually striking parts of neurons. Even so many neuron models are of point type and have no representation of space. In this thesis we will look at a range of neuronal models with the common property that we always include spatially extended dendrites. First we generalise Abbott’s “sum-over-trips” framework to include resonant currents. We also look at piece-wise linear (PWL) models and extend them to incorporate spatial structure in the form of dendrites. We look at the analytical construction of orbits for PWL models. By using both analytical and numerical Lyapunov exponent methods we explore phase space and in particular we look at mode-locked solutions. We will then construct the phase response curve (PRC) for a PWL system with compartmentally modelled dendrites. This sets us up so we can look at the effect of multiple PWL systems that are weakly coupled through gap junctions. We also attach a continuous dendrite to a PWL soma and investigate how the position of the gap junction influences network properties. After this we will present a short overview of neuronal plasticity with a special focus on the spatial effects. We also discuss attenuation of distal synaptic input and how this can be countered by dendritic democracy as this will become an integral part of our learning mechanisms. We will examine a number of different learning approaches including the tempotron and spike-time dependent plasticity. Here we will consider Poisson’s equation around a neural membrane. The membrane we focus on has Hodgkin-Huxley dynamics so we can study action potential propagation on the membrane. We present the Green’s function for the case of a one-dimensional membrane in a two-dimensional space. This will allow us to examine the action potential initiation and propagation in a multi-dimensional axon
Asymmetric ephaptic inhibition between compartmentalized olfactory receptor neurons.
In the Drosophila antenna, different subtypes of olfactory receptor neurons (ORNs) housed in the same sensory hair (sensillum) can inhibit each other non-synaptically. However, the mechanisms underlying this underexplored form of lateral inhibition remain unclear. Here we use recordings from pairs of sensilla impaled by the same tungsten electrode to demonstrate that direct electrical ("ephaptic") interactions mediate lateral inhibition between ORNs. Intriguingly, within individual sensilla, we find that ephaptic lateral inhibition is asymmetric such that one ORN exerts greater influence onto its neighbor. Serial block-face scanning electron microscopy of genetically identified ORNs and circuit modeling indicate that asymmetric lateral inhibition reflects a surprisingly simple mechanism: the physically larger ORN in a pair corresponds to the dominant neuron in ephaptic interactions. Thus, morphometric differences between compartmentalized ORNs account for highly specialized inhibitory interactions that govern information processing at the earliest stages of olfactory coding
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