1,664 research outputs found
Instability of synchronized motion in nonlocally coupled neural oscillators
We study nonlocally coupled Hodgkin-Huxley equations with excitatory and
inhibitory synaptic coupling. We investigate the linear stability of the
synchronized solution, and find numerically various nonuniform oscillatory
states such as chimera states, wavy states, clustering states, and
spatiotemporal chaos as a result of the instability.Comment: 8 pages, 9 figure
Cluster synchronization in an ensemble of neurons interacting through chemical synapses
In networks of periodically firing spiking neurons that are interconnected
with chemical synapses, we analyze cluster state, where an ensemble of neurons
are subdivided into a few clusters, in each of which neurons exhibit perfect
synchronization. To clarify stability of cluster state, we decompose linear
stability of the solution into two types of stabilities: stability of mean
state and stabilities of clusters. Computing Floquet matrices for these
stabilities, we clarify the total stability of cluster state for any types of
neurons and any strength of interactions even if the size of networks is
infinitely large. First, we apply this stability analysis to investigating
synchronization in the large ensemble of integrate-and-fire (IF) neurons. In
one-cluster state we find the change of stability of a cluster, which
elucidates that in-phase synchronization of IF neurons occurs with only
inhibitory synapses. Then, we investigate entrainment of two clusters of IF
neurons with different excitability. IF neurons with fast decaying synapses
show the low entrainment capability, which is explained by a pitchfork
bifurcation appearing in two-cluster state with change of synapse decay time
constant. Second, we analyze one-cluster state of Hodgkin-Huxley (HH) neurons
and discuss the difference in synchronization properties between IF neurons and
HH neurons.Comment: Notation for Jacobi matrix is changed. Accepted for publication in
Phys. Rev.
Improving the provision of Melbourne Health Familial Cancer services to Victoria’s Culturally and Linguistically Diverse (CALD) communities
Thermal Impact on Spiking Properties in Hodgkin-Huxley Neuron with Synaptic Stimulus
The effect of environmental temperature on neuronal spiking behaviors is
investigated by numerically simulating the temperature dependence of spiking
threshold of the Hodgkin-Huxley neuron subject to synaptic stimulus. We find
that the spiking threshold exhibits a global minimum in a "comfortable
temperature" range where spike initiation needs weakest synaptic strength,
indicating the occurrence of optimal use of synaptic transmission in neural
system. We further explore the biophysical origin of this phenomenon in ion
channel gating kinetics and also discuss its possible biological relevance in
information processing in neural systems.Comment: 10 pages, 4 figure
E-cadherin and cell adhesion: a role in architecture and function in the pancreatic islet
Background/Aims: The efficient secretion of insulin from beta-cells requires extensive intra-islet communication. The cell surface adhesion protein epithelial (E)-cadherin (ECAD) establishes and maintains epithelial tissues such as the islets of Langerhans. In this study, the role of ECAD in regulating insulin secretion from pseudoislets was investigated. Methods: The effect of an immuno-neutralising ECAD on gross morphology, cytosolic calcium signalling, direct cell-to-cell communication and insulin secretion was assessed by fura-2 microfluorimetry, Lucifer Yellow dye injection and insulin ELISA in an insulin-secreting model system. Results: Antibody blockade of ECAD reduces glucose-evoked changes in [Ca2+](i) and insulin secretion. Neutralisation of ECAD causes a breakdown in the glucose-stimulated synchronicity of calcium oscillations between discrete regions within the pseudoislet, and the transfer of dye from an individual cell within a cell cluster is attenuated in the absence of ECAD ligation, demonstrating that gap junction communication is disrupted. The functional consequence of neutralising ECAD is a significant reduction in insulin secretion. Conclusion: Cell adhesion via ECAD has distinct roles in the regulation of intercellular communication between beta-cells within islets, with potential repercussions for insulin secretion. Copyright (C) 2007 S. Karger AG, Basel
A near-infrared survey for new low-mass members in Alpha Per
We present a near-infrared (K'-band) survey of 0.7 square degree area in the
Alpha Persei open cluster (age = 90 Myr, distance = 182 pc) carried out with
the Omega-Prime camera on the Calar Alto 3.5-m telescope. Combining optical
data (Rc and Ic) obtained with the KPNO/MOSA detector and presented in Stauffer
et al. (1999) with the K' observations, a sample of new candidate members has
been extracted from the optical-infrared colour-magnitude diagram. The location
of these candidates in the colour-colour diagram suggests that two-thirds of
them are actually reddened background giants. About 20 new candidate members
with masses between 0.3 and 0.04 Msun are added to the 400 known Alpha Per
cluster members. If they are indeed Alpha Per members, four of the new
candidates would be brown dwarfs. We discuss the advantages and drawbacks of
the near-infrared survey as compared to the optical selection method. We also
describe the outcome of optical spectroscopy obtained with the Twin
spectrograph on the Calar Alto 3.5-m telescope for about 30 candidates,
including selected members from the optical sample presented in Barrado y
Navascues et al. (2002) and from our joint optical/infrared catalogue. These
results argue in favour of the optical selection method for this particular
cluster.Comment: 13 pages, 10 figures, 3 tables and 1 electronic table, accepted for
publication in A&
Capacitance fluctuations causing channel noise reduction in stochastic Hodgkin-Huxley systems
Voltage-dependent ion channels determine the electric properties of axonal
cell membranes. They not only allow the passage of ions through the cell
membrane but also contribute to an additional charging of the cell membrane
resulting in the so-called capacitance loading. The switching of the channel
gates between an open and a closed configuration is intrinsically related to
the movement of gating charge within the cell membrane. At the beginning of an
action potential the transient gating current is opposite to the direction of
the current of sodium ions through the membrane. Therefore, the excitability is
expected to become reduced due to the influence of a gating current. Our
stochastic Hodgkin-Huxley like modeling takes into account both the channel
noise -- i.e. the fluctuations of the number of open ion channels -- and the
capacitance fluctuations that result from the dynamics of the gating charge. We
investigate the spiking dynamics of membrane patches of variable size and
analyze the statistics of the spontaneous spiking. As a main result, we find
that the gating currents yield a drastic reduction of the spontaneous spiking
rate for sufficiently large ion channel clusters. Consequently, this
demonstrates a prominent mechanism for channel noise reduction.Comment: 18 page
Properties of the Chandra Sources in M81
The Chandra X-ray Observatory obtained a 50-ks observation of the central
region of M81 using the ACIS-S in imaging mode. The global properties of the 97
x-ray sources detected in the inner 8.3x8.3 arcmin field of M81 are examined.
Roughly half the sources are concentrated within the central bulge. The
remainder are distributed throughout the disk with the brightest disk sources
lying preferentially along spiral arms. The average hardness ratios of both
bulge and disk sources are consistent with power law spectra of index Gamma~1.6
indicative of a population of x-ray binaries. A group of much softer sources
are also present. The background source-subtracted logN-logS distribution of
the disk follows a power law of index ~ -0.5 with no change in slope over three
decades in flux. The logN-logS distribution of the bulge follows a similar
shape but with a steeper slope above ~4.0e+37 ergs/s. There is unresolved x-ray
flux from the bulge with a radial profile similar to that of the bulge sources.
This unresolved flux is softer than the average of the bulge sources and
extrapolating the bulge logN-logS distribution towards weaker sources can only
account for 20% of the unresolved flux. No strong time variability was observed
for any source with the exception of one bright, soft source.Comment: 5 pages, 3 color PS figures, to appear in ApJ
Frequency and phase synchronization of two coupled neurons with channel noise
We study the frequency and phase synchronization in two coupled identical and
nonidentical neurons with channel noise. The occupation number method is used
to model the neurons in the context of stochastic Hodgkin-Huxley model in which
the strength of of channel noise is represented by ion channel cluster size of
the initiation region of neuron. It is shown that frequency synchronization
only was achieved at arbitrary value of couple strength as long as two neurons'
channel cluster sizes are the same. We also show that the relative phase of
neurons can display profuse dynamic behavior under the combined action of
coupling and channel noise. Both qualitative and quantitative descriptions are
applied to describe the transitions between those behaviors. Relevance of our
findings to controlling neural synchronization experimentally is discussed.Comment: 8 pages, 10 figure
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