113,188 research outputs found
Selective gating of neuronal activity by intrinsic properties in distinct motor rhythms
This research has been supported by the Royal Society, Wellcome Trust (089319), and the Biotechnology and Biological Sciences Research Council (BB/L0011X/1). I thank Drs. Steve Soffe, Alan Roberts, Erik Svensson, Hong-Yan Zhang, and Stefan Pulver for commenting on the manuscript.Many neural circuits show fast reconfiguration following altered sensory or modulatory inputs to generate stereotyped outputs. In the motor circuit of Xenopus tadpoles, I study how certain voltage-dependent ionic currents affect firing thresholds and contribute to circuit reconfiguration to generate two distinct motor patterns, swimming and struggling. Firing thresholds of excitatory interneurons [i.e., descending interneurons (dINs)] in the swimming central pattern generator are raised by depolarization due to the inactivation of Na+ currents. In contrast, the thresholds of other types of neurons active in swimming or struggling are raised by hyperpolarization from the activation of fast transient K+ currents. The firing thresholds are then compared with the excitatory synaptic drives, which are revealed by blocking action potentials intracellularly using QX314 during swimming and struggling. During swimming, transient K+ currents lower neuronal excitability and gate out neurons with weak excitation, whereas their inactivation by strong excitation in other neurons increases excitability and enables fast synaptic potentials to drive reliable firing. During struggling, continuous sensory inputs lead to high levels of network excitation. This allows the inactivation of Na+ currents and suppression of dIN activity while inactivating transient K+ currents, recruiting neurons that are not active in swimming. Therefore, differential expression of these currents between neuron types can explain why synaptic strength does not predict firing reliability/intensity during swimming and struggling. These data show that intrinsic properties can override fast synaptic potentials, mediate circuit reconfiguration, and contribute to motorβpattern switching.Publisher PDFPeer reviewe
Holographic Schwinger effect in the confining background with D-instanton
Using the gauge-gravity duality, we study the holographic Schwinger effect by
performing the potential analysis on the confining D3- and D4-brane background
with D-instantons then evaluate the pair production/decay rate by taking
account into a fundamental string and a single flavor brane respectively. The
two confining backgrounds with D-instantons are obtained from the black
D(-1)-D3 and D0-D4 solution with a double Wick rotation. The total potential
and pair production/decay rate in the Schwinger effect are calculated
numerically by examining the NG action of a fundamental string and the DBI
action of a single flavor brane all in the presence of an electric field. In
both backgrounds our numerical calculation agrees with the critical electric
field evaluated from the DBI action and shows the potential barrier is
increased by the presence of the D-instantons, thus the production/decay rate
is suppressed by the D-instantons. Our interpretation is that particles in the
dual field theory could acquire an effective mass through the Chern-Simons
interaction or the theta term due to the presence of D-instantons so that the
pair production/decay rate in Schwinger effect is suppressed since it behaves
as . Our conclusion is in agreement with the previous results
obtained in the deconfined D(-1)-D3 background at zero temperature limit and
from the approach of the flavor brane in the D0-D4 background. In this sense,
this work may be also remarkable to study the phase transition in
Maxwell-Chern-Simons theory and observable effects by the theta angle in QCD.Comment: 2 tables,9 figures,23 page
The interaction of glueball and heavy-light flavoured meson in holographic QCD
We construct the D4/D8 brane configuration in the Witten-Sakai-Sugimoto model
by introducing a pair of heavy flavour brane with a heavy-light open string.
The multiplets created by the heavy-light string acquire mass due to the finite
separation of the heavy and light flavour branes thus they could be identified
as the heavy-light meson fields in this model. On the other hand the glueball
field is identified as the gravitational fluctuations carried by the close
string in the bulk, so this model is able to describe the interaction of
glueball and heavy-light meson through the open-close string interaction in
gauge-gravity duality. We explicitly derive the effective action for the
various glueballs and heavy-light mesons then numerically evaluate the
associated coupling constants. Afterwards the decay widths of various glueballs
to the lowest heavy-light meson, which is identified as meson, are
calculated by using our effective action. This work extends the previous
investigations of glueball in holographic QCD and it is also a further
prediction of glueball-meson interaction.Comment: 33 pages, 2 figures, 2 table
Glueball-baryon interactions in holographic QCD
Studying the Witten-Sakai-Sugimoto model with type IIA string theory, we find
the glueball-baryon interaction is predicted in this model. The glueball is
identified as the 11D gravitational waves or graviton described by the M5-brane
supergravity solution. Employing the relation of M-theory and type IIA string
theory, glueball is also 10D gravitational perturbations which are the excited
modes by close strings in the bulk of this model. On the other hand, baryon is
identified as a D4-brane wrapped on which is named as baryon vertex, so
the glueball-baryon interaction is nothing but the close string/baryon vertex
interaction in this model. Since the baryon vertex could be equivalently
treated as the instanton configurations on the flavor brane, we identify the
glueball-baryon interaction as "graviton-instanton" interaction in order to
describe it quantitatively by the quantum mechanical system for the collective
modes of baryons. So the effective Hamiltonian can be obtained by considering
the gravitational perturbations in the flavor brane action. With this
Hamiltonian, the amplitudes and the selection rules of the glueball-baryon
interaction can be analytically calculated in the strong coupling limit. We
show our calculations explicitly in two characteristic situations which are
"scalar and tensor glueball interacting with baryons". Although there is a long
way to go, our work provides a holographic way to understand the interactions
of baryons in hadronic physics and nuclear physics by the underlying string
theory.Comment: 16 pages, adding the Appendix C and transition amplitude in this
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