571 research outputs found
Discovering Spike Patterns in Neuronal Responses
When a cortical neuron is repeatedly injected with the same fluctuating current stimulus (frozen noise) the timing of the spikes is highly precise from trial to trial and the spike pattern appears to be unique. We show here that the same repeated stimulus can produce more than one reliable temporal pattern of spikes. A new method is introduced to find these patterns in raw multitrial data and is tested on surrogate data sets. Using it, multiple coexisting spike patterns were discovered in pyramidal cells recorded from rat prefrontal cortex in vitro, in data obtained in vivo from the middle temporal area of the monkey (Buracas et al., 1998) and from the cat lateral geniculate nucleus (Reinagel and Reid, 2002). The spike patterns lasted from a few tens of milliseconds in vitro to several seconds in vivo. We conclude that the prestimulus history of a neuron may influence the precise timing of the spikes in response to a stimulus over a wide range of time scales
Finding the event structure of neuronal spike trains
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Antagonistic effects of nearest-neighbor repulsion on the superconducting pairing dynamics in the doped Mott insulator regime
The nearest-neighbor superexchange-mediated mechanism for d_{x^2-y^2}-wave
superconductivity in the one-band Hubbard model faces the challenge that
nearest-neighbor Coulomb repulsion can be larger than superexchange. To answer
this question, we use cellular dynamical mean-field theory (CDMFT) with a
continuous-time quantum Monte Carlo solver to determine the superconducting
phase diagram as a function of temperature and doping for on-site repulsion
and nearest-neighbor repulsion . In the underdoped regime,
increases the CDMFT superconducting transition temperature even
though it decreases the superconducting order parameter at low temperature for
all dopings. However, decreases in the overdoped regime. We gain
insight into these paradoxical results through a detailed study of the
frequency dependence of the anomalous spectral function, extracted at finite
temperature via the MaxEntAux method for analytic continuation. A systematic
study of dynamical positive and negative contributions to pairing reveals that
even though has a high-frequency depairing contribution, it also has a low
frequency pairing contribution since it can reinforce superexchange through
. Retardation is thus crucial to understand pairing in doped Mott
insulators, as suggested by previous zero-temperature studies. We also comment
on the tendency to charge order for large and on the persistence of d-wave
superconductivity over extended- or s+d-wave.Comment: Latex, 16 pages, 8 figure
Information transmission in oscillatory neural activity
Periodic neural activity not locked to the stimulus or to motor responses is
usually ignored. Here, we present new tools for modeling and quantifying the
information transmission based on periodic neural activity that occurs with
quasi-random phase relative to the stimulus. We propose a model to reproduce
characteristic features of oscillatory spike trains, such as histograms of
inter-spike intervals and phase locking of spikes to an oscillatory influence.
The proposed model is based on an inhomogeneous Gamma process governed by a
density function that is a product of the usual stimulus-dependent rate and a
quasi-periodic function. Further, we present an analysis method generalizing
the direct method (Rieke et al, 1999; Brenner et al, 2000) to assess the
information content in such data. We demonstrate these tools on recordings from
relay cells in the lateral geniculate nucleus of the cat.Comment: 18 pages, 8 figures, to appear in Biological Cybernetic
Intrinsic gain modulation and adaptive neural coding
In many cases, the computation of a neural system can be reduced to a
receptive field, or a set of linear filters, and a thresholding function, or
gain curve, which determines the firing probability; this is known as a
linear/nonlinear model. In some forms of sensory adaptation, these linear
filters and gain curve adjust very rapidly to changes in the variance of a
randomly varying driving input. An apparently similar but previously unrelated
issue is the observation of gain control by background noise in cortical
neurons: the slope of the firing rate vs current (f-I) curve changes with the
variance of background random input. Here, we show a direct correspondence
between these two observations by relating variance-dependent changes in the
gain of f-I curves to characteristics of the changing empirical
linear/nonlinear model obtained by sampling. In the case that the underlying
system is fixed, we derive relationships relating the change of the gain with
respect to both mean and variance with the receptive fields derived from
reverse correlation on a white noise stimulus. Using two conductance-based
model neurons that display distinct gain modulation properties through a simple
change in parameters, we show that coding properties of both these models
quantitatively satisfy the predicted relationships. Our results describe how
both variance-dependent gain modulation and adaptive neural computation result
from intrinsic nonlinearity.Comment: 24 pages, 4 figures, 1 supporting informatio
Four-color multiplex real-Time PCR assay prototype targeting azithromycin resistance mutations in Mycoplasma genitalium
peer reviewedBackground: The worldwide expansion of macrolide-resistant Mycoplasma genitalium (MG) in cases of genital infections has led to an increased recurrence rate of these infections after first-line azithromycin treatment. By detecting the presence of azithromycin-resistant MG, the patient's antibiotic treatment can be targeted and the spread of resistance prevented. With this aim in mind, macrolide-resistance detection kits are helpful tools for the physician. Methods: Azithromycin resistance mutations in MG are targeted using a four-color multiplex real-Time RT-PCR assay. Tested targets include plasmid DNA (as positive controls) as well as macrolide-sensitive and macrolide-resistant genomic DNA from characterized cell lines and clinical samples. Results: The analytical data presented here were generated from plasmid DNA and genomic RNA/DNA and include adaptation to an internal control, specificity between targets, specificity vs non-MG species, limit of detection (LoD) and interference studies (co-infection and endogenous substances). The clinical data were based on the application of the assay to clinical samples characterized by sequencing. Conclusions: A new NAAT (nucleic acid amplification test) prototype has been developed in collaboration with the Diagenode s.a. company, this prototype targets MG and azithromycin-resistance mutations in that pathogen. © 2019 The Author(s)
A flexible component-based robot control architecture for hormonal modulation of behaviour and affect
This document is the Accepted Manuscritpt of a paper published in Proceedings of 18th Annual Conference, TAROS 2017, Guildford, UK, July 19–21, 2017. Under embargo. Embargo end date: 20 July 2018. The final publication is available at Springer via https://link.springer.com/chapter/10.1007%2F978-3-319-64107-2_36. © 2017 Springer, Cham.In this paper we present the foundations of an architecture that will support the wider context of our work, which is to explore the link between affect, perception and behaviour from an embodied perspective and assess their relevance to Human Robot Interaction (HRI). Our approach builds upon existing affect-based architectures by combining artificial hormones with discrete abstract components that are designed with the explicit consideration of influencing, and being receptive to, the wider affective state of the robot
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