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Neuromodulatory control of localized dendritic spiking in critical period cortex.
Sensory experience in early postnatal life, during so-called critical periods, restructures neural circuitry to enhance information processing1. Why the cortex is susceptible to sensory instruction in early life and why this susceptibility wanes with age are unclear. Here we define a developmentally restricted engagement of inhibitory circuitry that shapes localized dendritic activity and is needed for vision to drive the emergence of binocular visual responses in the mouse primary visual cortex. We find that at the peak of the critical period for binocular plasticity, acetylcholine released from the basal forebrain during periods of heightened arousal directly excites somatostatin (SST)-expressing interneurons. Their inhibition of pyramidal cell dendrites and of fast-spiking, parvalbumin-expressing interneurons enhances branch-specific dendritic responses and somatic spike rates within pyramidal cells. By adulthood, this cholinergic sensitivity is lost, and compartmentalized dendritic responses are absent but can be re-instated by optogenetic activation of SST cells. Conversely, suppressing SST cell activity during the critical period prevents the normal development of binocular receptive fields by impairing the maturation of ipsilateral eye inputs. This transient cholinergic modulation of SST cells, therefore, seems to orchestrate two features of neural plasticity-somatic disinhibition and compartmentalized dendritic spiking. Loss of this modulation may contribute to critical period closure
Gyro-induced acceleration of magnetic reconnection
The linear and nonlinear evolution of magnetic reconnection in collisionless
high-temperature plasmas with a strong guide field is analyzed on the basis of
a two-dimensional gyrofluid model. The linear growth rate of the reconnecting
instability is compared to analytical calculations over the whole spectrum of
linearly unstable wave numbers. In the strongly unstable regime (large \Delta
'), the nonlinear evolution of the reconnecting instability is found to undergo
two distinctive acceleration phases separated by a stall phase in which the
instantaneous growth rate decreases. The first acceleration phase is caused by
the formation of strong electric fields close to the X-point due to ion
gyration, while the second acceleration phase is driven by the development of
an open Petschek-like configuration due to both ion and electron temperature
effects. Furthermore, the maximum instantaneous growth rate is found to
increase dramatically over its linear value for decreasing diffusion layers.
This is a consequence of the fact that the peak instantaneous growth rate
becomes weakly dependent on the microscopic plasma parameters if the diffusion
region thickness is sufficiently smaller than the equilibrium magnetic field
scale length. When this condition is satisfied, the peak reconnection rate
asymptotes to a constant value.Comment: Accepted for publication on Physics of Plasma
Spitzer Observations of Galaxy Clusters
We present preliminary results of a project to study three rich nearby clusters of galaxies with the Spitzer space telescope. The Spitzer observations in the four IRAC and three MIPS bands cover a region up to three virial radii, approximately, and have been recently completed. On the basis of the first Spitzer images, we followed up spectroscopically the far-infrared sources with the multi-fiber spectrograph HYDRA on the WIYN telescope. 70% of the sources brighter than 0.3 mJy at 24 μm and r’ < 20.5 have been observed for a total of 1078 spectra. For 87% of them we were able to measure redshifts obtaining 50 to 100 members for the different clusters. This first study shows that the far-IR sources in these clusters are predominantly powered by star formation and clustered in regions far from the center. In the case of A1763, they seem to be situated along a filament supporting the idea of infalling galaxies experiencing bursts of star formation during their first contact with the hot intra-cluster medium
An extension problem for the CR fractional Laplacian
We show that the conformally invariant fractional powers of the sub-Laplacian
on the Heisenberg group are given in terms of the scattering operator for an
extension problem to the Siegel upper halfspace. Remarkably, this extension
problem is different from the one studied, among others, by Caffarelli and
Silvestre.Comment: 33 pages. arXiv admin note: text overlap with arXiv:0709.1103 by
other author
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State-Dependent Subnetworks of Parvalbumin-Expressing Interneurons in Neocortex.
Brain state determines patterns of spiking output that underlie behavior. In neocortex, brain state is reflected in the spontaneous activity of the network, which is regulated in part by neuromodulatory input from the brain stem and by local inhibition. We find that fast-spiking, parvalbumin-expressing inhibitory neurons, which exert state-dependent control of network gain and spike patterns, cluster into two stable and functionally distinct subnetworks that are differentially engaged by ascending neuromodulation. One group is excited as a function of increased arousal state; this excitation is driven in part by the increase in cortical norepinephrine that occurs when the locus coeruleus is active. A second group is suppressed during movement when acetylcholine is released into the cortex via projections from the nucleus basalis. These data establish the presence of functionally independent subnetworks of Parvalbumin (PV) cells in the upper layers of the neocortex that are differentially engaged by the ascending reticular activating system
Steering Bose-Einstein condensates despite time symmetry
A Bose-Einstein condensate in an oscillating spatially asymmetric potential
is shown to exhibit a directed current for unbiased initial conditions despite
time symmetry. This phenomenon occurs only if the interaction between atoms,
treated in mean-field approximation, exceeds a critical value. Our findings can
be described with a three-mode model (TMM). These TMM results corroborate well
with a many-body study over a time scale which increases with increasing atom
number. The duration of this time scale probes the validity of the used
mean-field approximation.Comment: 4 pages, 5 figure
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