Preparing pseudo-pure states with controlled-transfer gates

The preparation of pseudo-pure states plays a central role in the implementation of quantum information processing in high temperature ensemble systems, such as nuclear magnetic resonance. Here we describe a simple approach based on controlled-transfer gates which permits pseudo-pure states to be prepared efficiently using spatial averaging techniques.Comment: Significantly revised and extended: now 7 pages including 3 figures; Phys. Rev. A (in press

Multisensory Integration Produces an Initial Response Enhancement

The brain has evolved the ability to integrate information across the senses in order to improve the detection and disambiguation of biologically significant events. This multisensory synthesis of information leads to faster (and more accurate) behavioral responses, yet the underlying neural mechanisms by which these responses are speeded are as yet unclear. The aim of these experiments was to evaluate the temporal properties of multisensory enhancement in the physiological responses of neurons in the superior colliculus (SC). Of specific interest was the temporal evolution of their responses to individual modality-specific stimuli as well as to cross-modal combinations of these stimuli. The results demonstrate that cross-modal stimuli typically elicit faster, more robust, and more reliable physiological responses than do their modality-specific component stimuli. Response measures sensitive to the time domain showed that these multisensory responses were enhanced from their very onset, and that the acceleration of the enhancement was greatest within the first 40ms (or 50% of the response). The latter half of the multisensory response was typically only as robust and informative as predicted by a linear combination of the unisensory component responses. These results may reveal some of the key physiological changes underlying many of the SC-mediated behavioral benefits of multisensory integration

Temporal Profiles of Response Enhancement in Multisensory Integration

Animals have evolved multiple senses that transduce different forms of energy as a way of increasing their sensitivity to environmental events. Each sense provides a unique and independent perspective on the world, and very often a single event stimulates several of them. In order to make best use of the available information, the brain has also evolved the capacity to integrate information across the senses (“multisensory integration”). This facilitates the detection, localization, and identification of a given event, and has obvious survival value for the individual and the species. Multisensory responses in the superior colliculus (SC) evidence shorter latencies and are more robust at their onset. This is the phenomenon of initial response enhancement in multisensory integration, which is believed to represent a real time fusion of information across the senses. The present paper reviews two recent reports describing how the timing and robustness of sensory responses change as a consequence of multisensory integration in the model system of the SC

Non-Stationarity in Multisensory Neurons in the Superior Colliculus

The superior colliculus (SC) integrates information from multiple sensory modalities to facilitate the detection and localization of salient events. The efficacy of “multisensory integration” is traditionally measured by comparing the magnitude of the response elicited by a cross-modal stimulus to the responses elicited by its modality-specific component stimuli, and because there is an element of randomness in the system, these calculations are made using response values averaged over multiple stimulus presentations in an experiment. Recent evidence suggests that multisensory integration in the SC is highly plastic and these neurons adapt to specific anomalous stimulus configurations. This raises the question whether such adaptation occurs during an experiment with traditional stimulus configurations; that is, whether the state of the neuron and its integrative principles are the same at the beginning and end of the experiment, or whether they are altered as a consequence of exposure to the testing stimuli even when they are pseudo-randomly interleaved. We find that unisensory and multisensory responses do change during an experiment, and that these changes are predictable. Responses that are initially weak tend to potentiate, responses that are initially strong tend to habituate, and the efficacy of multisensory integration waxes or wanes accordingly during the experiment as predicted by the “principle of inverse effectiveness.” These changes are presumed to reflect two competing mechanisms in the SC: potentiation reflects increases in the expectation that a stimulus will occur at a given location relative to others, and habituation reflects decreases in stimulus novelty. These findings indicate plasticity in multisensory integration that allows animals to adapt to rapidly changing environmental events while suggesting important caveats in the interpretation of experimental data: the neuron studied at the beginning of an experiment is not the same at the end of it

An Emergent Model of Multisensory Integration in Superior Colliculus Neurons

Neurons in the cat superior colliculus (SC) integrate information from different senses to enhance their responses to cross-modal stimuli. These multisensory SC neurons receive multiple converging unisensory inputs from many sources; those received from association cortex are critical for the manifestation of multisensory integration. The mechanisms underlying this characteristic property of SC neurons are not completely understood, but can be clarified with the use of mathematical models and computer simulations. Thus the objective of the current effort was to present a plausible model that can explain the main physiological features of multisensory integration based on the current neurological literature regarding the influences received by SC from cortical and subcortical sources. The model assumes the presence of competitive mechanisms between inputs, nonlinearities in NMDA receptor responses, and provides a priori synaptic weights to mimic the normal responses of SC neurons. As a result, it provides a basis for understanding the dependence of multisensory enhancement on an intact association cortex, and simulates the changes in the SC response that occur during NMDA receptor blockade. Finally, it makes testable predictions about why significant response differences are obtained in multisensory SC neurons when they are confronted with pairs of cross-modal and within-modal stimuli. By postulating plausible biological mechanisms to complement those that are already known, the model provides a basis for understanding how SC neurons are capable of engaging in this remarkable process

Postnatal Experiences Influence How the Brain Integrates Information from Different Senses

Sensory processing disorder (SPD) is characterized by anomalous reactions to, and integration of, sensory cues. Although the underlying etiology of SPD is unknown, one brain region likely to reflect these sensory and behavioral anomalies is the superior colliculus (SC), a structure involved in the synthesis of information from multiple sensory modalities and the control of overt orientation responses. In the present review we describe normal functional properties of this structure, the manner in which its individual neurons integrate cues from different senses, and the overt SC-mediated behaviors that are believed to manifest this “multisensory integration.” Of particular interest here is how SC neurons develop their capacity to engage in multisensory integration during early postnatal life as a consequence of early sensory experience, and the intimate communication between cortex and the midbrain that makes this developmental process possible

Cohesin Releases DNA through Asymmetric ATPase-Driven Ring Opening

Cohesin stably holds together the sister chromatids from S phase until mitosis. To do so, cohesin must be protected against its cellular antagonist Wapl. Eco1 acetylates cohesin's Smc3 subunit, which locks together the sister DNAs. We used yeast genetics to dissect how Wapl drives cohesin from chromatin and identified mutants of cohesin that are impaired in ATPase activity but remarkably confer robust cohesion that bypasses the need for the cohesin protectors Eco1 in yeast and Sororin in human cells. We uncover a functional asymmetry within the heart of cohesin's highly conserved ABC-like ATPase machinery and find that both ATPase sites contribute to DNA loading, whereas DNA release is controlled specifically by one site. We propose that Smc3 acetylation locks cohesin rings around the sister chromatids by counteracting an activity associated with one of cohesin's two ATPase sites. Tight regulation of DNA entrapment and release by the cohesin complex is crucial for its multiple cellular functions. Elbatsh et al. find that cohesin's release from DNA requires an activity associated with one of its ATPase sites, whereas both sites control cohesin's loading onto DNA

Alcohol consumption and sport: a cross-sectional study of alcohol management practices associated with at-risk alcohol consumption at community football clubs

BackgroundExcessive alcohol consumption is responsible for considerable harm from chronic disease and injury. Within most developed countries, members of sporting clubs participate in at-risk alcohol consumption at levels above that of communities generally. There has been limited research investigating the predictors of at-risk alcohol consumption in sporting settings, particularly at the non-elite level. The purpose of this study was to examine the association between the alcohol management practices and characteristics of community football clubs and at-risk alcohol consumption by club members.MethodsA cross sectional survey of community football club management representatives and members was conducted. Logistic regression analysis (adjusting for clustering by club) was used to determine the association between the alcohol management practices (including alcohol management policy, alcohol-related sponsorship, availability of low- and non-alcoholic drinks, and alcohol-related promotions, awards and prizes) and characteristics (football code, size and location) of sporting clubs and at-risk alcohol consumption by club members.ResultsMembers of clubs that served alcohol to intoxicated people [OR: 2.23 (95% CI: 1.26-3.93)], conducted &lsquo;happy hour&rsquo; promotions [OR: 2.84 (95% CI: 1.84-4.38)] or provided alcohol-only awards and prizes [OR: 1.80 (95% CI: 1.16-2.80)] were at significantly greater odds of consuming alcohol at risky levels than members of clubs that did not have such alcohol management practices. At-risk alcohol consumption was also more likely among members of clubs with less than 150 players compared with larger clubs [OR:1.45 (95% CI: 1.02-2.05)] and amongst members of particular football codes.ConclusionsThe findings of this study suggest a need and opportunity for the implementation of alcohol harm reduction strategies targeting specific alcohol management practices at community football clubs.<br /