Auto-structure of spike trains matters for testing on synchronous activity

Poster presentation: Coordinated neuronal activity across many neurons, i.e. synchronous or spatiotemporal pattern, had been believed to be a major component of neuronal activity. However, the discussion if coordinated activity really exists remained heated and controversial. A major uncertainty was that many analysis approaches either ignored the auto-structure of the spiking activity, assumed a very simplified model (poissonian firing), or changed the auto-structure by spike jittering. We studied whether a statistical inference that tests whether coordinated activity is occurring beyond chance can be made false if one ignores or changes the real auto-structure of recorded data. To this end, we investigated the distribution of coincident spikes in mutually independent spike-trains modeled as renewal processes. We considered Gamma processes with different shape parameters as well as renewal processes in which the ISI distribution is log-normal. For Gamma processes of integer order, we calculated the mean number of coincident spikes, as well as the Fano factor of the coincidences, analytically. We determined how these measures depend on the bin width and also investigated how they depend on the firing rate, and on rate difference between the neurons. We used Monte-Carlo simulations to estimate the whole distribution for these parameters and also for other values of gamma. Moreover, we considered the effect of dithering for both of these processes and saw that while dithering does not change the average number of coincidences, it does change the shape of the coincidence distribution. Our major findings are: 1) the width of the coincidence count distribution depends very critically and in a non-trivial way on the detailed properties of the inter-spike interval distribution, 2) the dependencies of the Fano factor on the coefficient of variation of the ISI distribution are complex and mostly non-monotonic. Moreover, the Fano factor depends on the very detailed properties of the individual point processes, and cannot be predicted by the CV alone. Hence, given a recorded data set, the estimated value of CV of the ISI distribution is not sufficient to predict the Fano factor of the coincidence count distribution, and 3) spike jittering, even if it is as small as a fraction of the expected ISI, can falsify the inference on coordinated firing. In most of the tested cases and especially for complex synchronous and spatiotemporal pattern across many neurons, spike jittering increased the likelihood of false positive finding very strongly. Last, we discuss a procedure [1] that considers the complete auto-structure of each individual spike-train for testing whether synchrony firing occurs at chance and therefore overcomes the danger of an increased level of false positives

Anticipated results from dust experiments on cometary missions

The major scientific objectives of a mission are: to determine the chemical nature and physical structure of comet nuclei, and to characterize the changes that occur as a function of time orbital position; to characterize the chemical and physical nature of the atmospheres and ionospheres of comets as well as the processes that occur in them, and to characterize the development of the atmospheres and ionospheres as functions of time and orbital position; and to determine the nature of comet tails and processes by which they are formed, and to characterize the interaction of comets with the solar wind. Since dust is a major constituent of a comet, the achievement of these goals requires the intensive study of the paticulate emission from a comet

Climate Change, Risk and Grain Production in China

This paper employs the production function-based method proposed by Just and Pope (1978, 1979) to explicitly analyze production risk in the context of Chinese grain farming and climate change, and test for a potential endogeneity of climate factors in Chinese grain production. Our results indicate that China might, at least in the short run, become a net beneficiary of climate change. In particular, we find that increases in annual average temperature increase mean output at the margin and at the same time lead to a reduction of production risk. Further calculations suggest that a 1 °C increase in annual average temperature would entail an economic benefit of $1.1 billion due to the increasing mean output. Furthermore, a Hausman test reveals no endogeneity of climate variables in Chinese grain production.Agriculture, grain production, climate change, production risk, China, Crop Production/Industries, Environmental Economics and Policy, Risk and Uncertainty, Q1, Q54,

Direct Dating of Human Fossils

The methods that can be used for the direct dating of human remains comprise of radiocarbon, U-series, electron spin resonance (ESR), and amino acid racemization (AAR). This review gives an introduction to these methods in the context of dating human bones and teeth. Recent advances in ultrafiltration techniques have expanded the dating range of radiocarbon. It now seems feasible to reliably date bones up to 55,000 years. New developments in laser ablation mass spectrometry permit the in situ analysis of U-series isotopes, thus providing a rapid and virtually non-destructive dating method back to about 300,000 years. This is of particular importance when used in conjunction with non-destructive ESR analysis. New approaches in AAR analysis may lead to a renaissance of this method. The potential and present limitations of these direct dating techniques are discussed for sites relevant to the reconstruction of modern human evolution, including Florisbad, Border Cave, Tabun, Skhul, Qafzeh, Vindija, Banyoles, and Lake Mungo

Letter from S. C. Grun to P. M. Colson

Letter from S. C. Grun to P. M. Colson. The one-page handwritten note is dated 18 May 1907

Future European Ground Segment

lhe existing European ground infrastructure is capable to support earth observation satellites, the present ARIANE program and scientific manned spaceflight missions as demonstrated during the first German Spacelab D 1 mission flown as payload onboard NSTS in October 85. Future European space program like EURECA, COLUMBUS, HERMES, ARIANE 5, DRS and scientifi~ satellites will require a ground based end-to-end o~eration and verification infrastructure (GEOVI) of a new order of magnitude. Individual program needs and required user support ground segments exceed the very tight budgetary frame available for the European space com~unity (agencies and i ndust.ry) . Investments are\u27 necessary for i ndust ri a 1 development faci- 1 iti es to ~upport the AIV phase, support facilities for development and operation, launch and landing facilities operation~ facilities for mission and payload control and payload data facilities for data dissemination, archiving, retrieval etc

Ground Based Operations Support By Artificial Intelligence

The increasing number and sustained duration of future manned or unmanned space missions, the growing complexity of spacecraft, the increasing variety of payloads and the demand for maximum economic efficiency of space operations will lead to the evolution of large-scale ground based operations infrastructures of increasing complexity and sophistication. In order to enhance the manageability and safety of operations under these aspects and to limit the amount of highly skilled personnel required, thereby supporting an early economic attractivity of space, the utilization of Artificial Intelligence (AI) as support for ground based operations appears to be a promising method which has received growing attention in recent years. In this paper, after an outline of the main areas of ground based operations support by AI, also these questions of the management of large distributed AI-systems within a complex communication environment are therefore addressed and required technology developments indicated which comprise in particular the direct or indirect utilization of databases and simulation facilities as knowledge sources for large AI-systems

Answer format effects revisited

The effect of answer formats presented to respondents in written surveys are investigated for two constructs (attitudes and behavioral intentions) and three response scales (binary, ordinal and metric). Results indicate that (1) formats differ in their susceptibility to response styles but lead to the same results with respect to average values and underlying dimensions; (2) binary format is quicker to complete and perceived as quicker while all formats are perceived as equally simple, pleasant, and useful to express feelings; (3) an interaction between the construct measured and the answer format clearly exists which should be investigated more systematically in future research