Correlation entropy of synaptic input-output dynamics

The responses of synapses in the neocortex show highly stochastic and nonlinear behavior. The microscopic dynamics underlying this behavior, and its computational consequences during natural patterns of synaptic input, are not explained by conventional macroscopic models of deterministic ensemble mean dynamics. Here, we introduce the correlation entropy of the synaptic input-output map as a measure of synaptic reliability which explicitly includes the microscopic dynamics. Applying this to experimental data, we find that cortical synapses show a low-dimensional chaos driven by the natural input pattern.Comment: 7 pages, 6 Figures (7 figure files

Quantifying impacts of short-term plasticity on neuronal information transfer

Short-term changes in efficacy have been postulated to enhance the ability of synapses to transmit information between neurons, and within neuronal networks. Even at the level of connections between single neurons, direct confirmation of this simple conjecture has proven elusive. By combining paired-cell recordings, realistic synaptic modelling and information theory, we provide evidence that short-term plasticity can not only improve, but also reduce information transfer between neurons. We focus on a concrete example in rat neocortex, but our results may generalise to other systems. When information is contained in the timings of individual spikes, we find that facilitation, depression and recovery affect information transmission in proportion to their impacts upon the probability of neurotransmitter release. When information is instead conveyed by mean spike rate only, the influences of short-term plasticity critically depend on the range of spike frequencies that the target network can distinguish (its effective dynamic range). Our results suggest that to efficiently transmit information, the brain must match synaptic type, coding strategy and network connectivity during development and behaviour.Comment: Accepted for publication in Phys Rev E. 42 pages in referee format, 9 figure

Fidelity for Multimode Thermal Squeezed States

In the theory of quantum transmission of information the concept of fidelity plays a fundamental role. An important class of channels, which can be experimentally realized in quantum optics, is that of Gaussian quantum channels. In this work we present a general formula for fidelity in the case of two arbitrary Gaussian states. From this formula one can get a previous result (H. Scutaru, J. Phys. A: Mat. Gen {\bf 31}, 3659 (1998)), for the case of a single mode; or, one can apply it to obtain a closed compact expression for multimode thermal states.Comment: 5 pages, RevTex, submitted to Phys. Rev.

Influence of Diporeia Density on Diet Composition, Relative Abundance, and Energy Density of Planktivorous Fishes in Southeast Lake Michigan

The benthic amphipod Diporeia spp. is an important prey for many fish in offshore areas of the Great Lakes, but its abundance has been rapidly decreasing. To assess the influence of Diporeia availability on the food habits, relative abundance, and energetics of planktivorous fish, the diet composition, catch per unit effort (CPUE), and energy density of plantkivorous fish in southeast Lake Michigan during 2000–2001 were compared among locations with different Diporeia densities. Diporeia densities at St. Joseph, Michigan, were near 0/m2 over much of the bottom but averaged more than 3,800/m2 at Muskegon and Little Sable Point, Michigan. Consistent with these differences in Diporeia density, fish diet composition, CPUE, and energy density varied spatially. For example, alternative prey types comprised a larger fraction of the diets of bloater Coregonus hoyi, large (>100 mm total length) alewife Alosa pseudoharengus, and slimy sculpin Cottus cognatus at St. Joseph than at Muskegon and Little Sable Point. This pattern was seasonally dependent for alewives and bloaters because Diporeia were eaten mainly in June. Food biomass per stomach was not lower at St. Joseph than elsewhere, suggesting that the spatial variation in diet composition was due to greater consumption of alternative prey by fish at St. Joseph. Although slimy sculpin and bloaters were able to feed on alternative prey, the CPUE of these species at certain depths was considerably lower at St. Joseph than at Muskegon or Little Sable Point, indicating that Diporeia availability may also influence fish abundance and distribution. Finally, a link between Diporeia density and fish energetics was suggested by the comparatively low energy density of deepwater sculpin Myoxocephalus thompsonii and large alewives at St. Joseph, a result that may reflect the low energy content of other prey relative to Diporeia.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141042/1/tafs0588.pd

Effect of acute copper sulfate exposure on olfactory responses to amino acids and pheromones in goldfish (Carassius auratus)

Exposure of olfactory epithelium to environmentally relevant concentrations of copper disrupts olfaction in fish. To examine the dynamics of recovery at both functional and morphological levels after acute copper exposure, unilateral exposure of goldfish olfactory epithelia to 100 μM CuSO4 (10 min) was followed by electro-olfactogram (EOG) recording and scanning electron microscopy. Sensitivity to amino acids (L-arginine and L-serine), generally considered food-related odorants, recovered most rapidly (three days), followed by that to catecholamines(3-O-methoxytyramine),bileacids(taurolithocholic acid) and the steroid pheromone, 17,20 -dihydroxy-4-pregnen- 3-one 20-sulfate, which took 28 days to reach full recovery. Sensitivity to the postovulatory pheromone prostaglandin F2R had not fully recovered even at 28 days. These changes in sensitivity were correlated with changes in the recovery of ciliated and microvillous receptor cell types. Microvillous cells appeared largely unaffected by CuSO4 treatment. Cilia in ciliated receptor neurones, however, appeared damaged one day post-treatment and were virtually absent after three days but had begun to recover after 14 days. Together, these results support the hypothesis that microvillous receptor neurones detect amino acids whereas ciliated receptor neurones were not functional and are responsible for detection of social stimuli (bile acidsandpheromones).Furthermore, differences in sensitivity to copper may be due to different transduction pathways in the different cell types

Autonomous, agile micro-satellites, and supporting technologies

This paper updates the on-going effort at Lawrence Livermore National Laboratory to develop autonomous, agile micro-satellites (MicroSats). The objective of this development effort is to develop MicroSats weighing only a few tens of kilograms, that are able to autonomously perform precision maneuvers and can be used telerobotically in a variety of mission modes. The required capabilities include satellite rendezvous, inspection, proximity-operations, docking, and servicing. The MicroSat carries an integrated proximity-operations sensor-suite incorporating advanced avionics. A new self-pressurizing propulsion system utilizing a miniaturized pump and non-toxic mono-propellant hydrogen peroxide was successfully tested. This system can provide a nominal 25 kg MicroSat with 200-300 m/s delta-v including a warm-gas attitude control system. The avionics is based on the latest PowerPC processor using a CompactPCI bus architecture, which is modular, high-performance and processor-independent. This leverages commercial-off-the-shelf (COTS) technologies and minimizes the effects of future changes in processors. The MicroSat software development environment uses the Vx-Works real-time operating system (RTOS) that provides a rapid development environment for integration of new software modules, allowing early integration and test. We will summarize results of recent integrated ground flight testing of our latest non-toxic pumped propulsion MicroSat testbed vehicle operated on our unique dynamic air-rail

RIC-7 Promotes Neuropeptide Secretion

Secretion of neurotransmitters and neuropeptides is mediated by exocytosis of distinct secretory organelles, synaptic vesicles (SVs) and dense core vesicles (DCVs) respectively. Relatively little is known about factors that differentially regulate SV and DCV secretion. Here we identify a novel protein RIC-7 that is required for neuropeptide secretion in Caenorhabditis elegans. The RIC-7 protein is expressed in all neurons and is localized to presynaptic terminals. Imaging, electrophysiology, and behavioral analysis of ric-7 mutants indicates that acetylcholine release occurs normally, while neuropeptide release is significantly decreased. These results suggest that RIC-7 promotes DCV–mediated secretion