Evolution and Analysis of Embodied Spiking Neural Networks Reveals Task-Specific Clusters of Effective Networks

Elucidating principles that underlie computation in neural networks is currently a major research topic of interest in neuroscience. Transfer Entropy (TE) is increasingly used as a tool to bridge the gap between network structure, function, and behavior in fMRI studies. Computational models allow us to bridge the gap even further by directly associating individual neuron activity with behavior. However, most computational models that have analyzed embodied behaviors have employed non-spiking neurons. On the other hand, computational models that employ spiking neural networks tend to be restricted to disembodied tasks. We show for the first time the artificial evolution and TE-analysis of embodied spiking neural networks to perform a cognitively-interesting behavior. Specifically, we evolved an agent controlled by an Izhikevich neural network to perform a visual categorization task. The smallest networks capable of performing the task were found by repeating evolutionary runs with different network sizes. Informational analysis of the best solution revealed task-specific TE-network clusters, suggesting that within-task homogeneity and across-task heterogeneity were key to behavioral success. Moreover, analysis of the ensemble of solutions revealed that task-specificity of TE-network clusters correlated with fitness. This provides an empirically testable hypothesis that links network structure to behavior.Comment: Camera ready version of accepted for GECCO'1

Masterov Kliuch and the Early Upper Palaeolithic of the Transbaikal, Siberia

In 1996, archaeological excavations were conducted at the Masterov Kliuch site, located east of Lake Baikal, Siberia. Three archaeological components were uncovered, all occurring in colluvial deposits. The two lower components (I and II) are Palaeolithic in age and character. Component I is an early Upper Palaeolithic industry dated to 32,500-30,000 years ago (B.P.), and is in a primary context. Component II is undated but is also assignable to the early Upper Palaeolithic based on typology, although it appears to have been redeposited. Artifact assemblages from these two components are blade-based and include retouched blades and flakes, knives, denticulates, end scrapers, gravers, and burins. Component III represents a Bronze Age occupation dated to around 2900 B.P. The Palaeolithic industries at Masterov Kliuch are technologically/typologically similar to other initial Upper Palaeolithic industries in Siberia, and appear to represent some of the easternmost manifestations of an early Upper Palaeolithic technocomplex that spanned inner Asia from Uzbekistan to the Transbaikal between about 42,000 and 30,000 B.P. Our findings have further implications for Upper Palaeolithic research in northern Asia, especially regarding site formation processes and hunter-gatherer raw material procurement. First, like Masterov Kliuch, most early Upper Palaeolithic sites across northern Asia lie in colluvial settings and may not be in pristine, primary contexts, so that interpretations of stone features such as hearths or dwellings may be suspect. Second, study of the Masterov Kliuch lithic industries indicates that huntergatherers exclusively utilized local lithic resources in the manufacture of tools, and that raw material procurement strategies were embedded within other subsistence pursuits. This pattern of local, embedded raw material procurement is seen in virtually all other early Upper Palaeolithic sites in Siberia, while "logistical," longdistance procurement strategies, characteristic of the early Upper Palaeolithic of western Eurasia, did not appear in Siberia until much later in time, after about 25,000 B.P. KEYWORDS: Siberia, early Upper Palaeolithic, geoarchaeology, lithic technology, raw material procurement

Study of the performance and capability of the new ultra-fast 2 GSample/s FADC data acquisition system of the MAGIC telescope

In February 2007 the MAGIC Air Cherenkov Telescope for gamma-ray astronomy was fully upgraded with an ultra fast 2 GSamples/s digitization system. Since the Cherenkov light flashes are very short, a fast readout can minimize the influence of the background from the light of the night sky. Also, the time structure of the event is an additional parameter to reduce the background from unwanted hadronic showers. An overview of the performance of the new system and its impact on the sensitivity of the MAGIC instrument will be presented.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of the MAGIC Collaboratio

Is the NIH policy for sharing GWAS data running the risk of being counterproductive?

Through their current policy on data sharing, the National Institutes of Health (NIH) are inadvertently placing a serious and potentially insuperable burden upon non-US researchers who perform patient-based genomics studies in collaboration with US institutions. Because this policy could adversely affect future transnational scientific collaborations, we explore some of its likely consequences and suggest possible courses of remedial action wherever feasible

Dirac Relation and Renormalization Group Equations for Electric and Magnetic Fine Structure Constants

The quantum field theory describing electric and magnetic charges and revealing a dual symmetry was developed in the Zwanziger formalism. The renormalization group (RG) equations for both fine structure constants - electric $\alpha$ and magnetic $\tilde \alpha$ - were obtained. It was shown that the Dirac relation is valid for the renormalized $\alpha$ and $\tilde \alpha$ at the arbitrary scale, but these RG equations can be considered perturbatively only in the small region: $0.25 \stackrel{<}{\sim} \alpha, \tilde \alpha \stackrel{<}{\sim} 1$ with $\tilde \alpha$ given by the Dirac relation: $\alpha {\tilde \alpha}$ = 1/4.Comment: 15 pages, 4 figures, made corrections of physics after comments from Kim Milto

Self-consistent model for ambipolar tunneling in quantum-well systems

We present a self-consistent approach to describe ambipolar tunneling in asymmetrical double quantum wells under steady-state excitation and extend the results to the case of tunneling from a near-surface quantum well to surface states. The results of the model compare very well with the behavior observed in photoluminescence experiments in $InGaAs/InP$ asymmetric double quantum wells and in near-surface $AlGaAs/GaAs$ single quantum wells.Comment: 10 pages, REVTeX 3.

When the brain takes 'BOLD' steps: Real-time fMRI neurofeedback can further enhance the ability to gradually self-regulate regional brain activation

Brain-computer interfaces (BCIs) based on real-time functional magnetic resonance imaging (rtfMRI) are currently explored in the context of developing alternative (motor-independent) communication and control means for the severely disabled. In such BCI systems, the user encodes a particular intention (e.g., an answer to a question or an intended action) by evoking specific mental activity resulting in a distinct brain state that can be decoded from fMRI activation. One goal in this context is to increase the degrees of freedom in encoding different intentions, i.e., to allow the BCI user to choose from as many options as possible. Recently, the ability to voluntarily modulate spatial and/or temporal blood oxygenation level-dependent (BOLD)-signal features has been explored implementing different mental tasks and/or different encoding time intervals, respectively. Our two-session fMRI feasibility study systematically investigated for the first time the possibility of using magnitudinal BOLD-signal features for intention encoding. Particularly, in our novel paradigm, participants (n=10) were asked to alternately self-regulate their regional brain-activation level to 30%, 60% or 90% of their maximal capacity by applying a selected activation strategy (i.e., performing a mental task, e.g., inner speech) and modulation strategies (e.g., using different speech rates) suggested by the experimenters. In a second step, we tested the hypothesis that the additional availability of feedback information on the current BOLD-signal level within a region of interest improves the gradual-self regulation performance. Therefore, participants were provided with neurofeedback in one of the two fMRI sessions. Our results show that the majority of the participants were able to gradually self-regulate regional brain activation to at least two different target levels even in the absence of neurofeedback. When provided with continuous feedback on their current BOLD-signal level, most participants further enhanced their gradual self-regulation ability. Our findings were observed across a wide variety of mental tasks and across clinical MR field strengths (i.e., at 1.5T and 3T), indicating that these findings are robust and can be generalized across mental tasks and scanner types. The suggested novel parametric activation paradigm enriches the spectrum of current rtfMRI-neurofeedback and BCI methodology and has considerable potential for fundamental and clinical neuroscience applications

Sound Categories Are Represented as Distributed Patterns in the Human Auditory Cortex

SummaryThe ability to recognize sounds allows humans and animals to efficiently detect behaviorally relevant events, even in the absence of visual information. Sound recognition in the human brain has been assumed to proceed through several functionally specialized areas, culminating in cortical modules where category-specific processing is carried out [1–5]. In the present high-resolution fMRI experiment, we challenged this model by using well-controlled natural auditory stimuli and by employing an advanced analysis strategy based on an iterative machine-learning algorithm [6] that allows modeling of spatially distributed, as well as localized, response patterns. Sounds of cats, female singers, acoustic guitars, and tones were controlled for their time-varying spectral characteristics and presented to subjects at three different pitch levels. Sound category information—not detectable with conventional contrast-based methods analysis—could be detected with multivoxel pattern analyses and attributed to spatially distributed areas over the supratemporal cortices. A more localized pattern was observed for processing of pitch laterally to primary auditory areas. Our findings indicate that distributed neuronal populations within the human auditory cortices, including areas conventionally associated with lower-level auditory processing, entail categorical representations of sounds beyond their physical properties

Platelet inhibitors versus anticoagulants for prevention of aorto-coronary bypass graft occlusion

The effects of the antiaggregant substance ticlopidine and of the anticoagulant acenocoumarol on patency rates of aorto-coronary bypass grafts were compared in a prospective randomized trial. Ticlopidine, 250 mg b.i.d. was administered orally from the first postoperative day till angiography, while anticoagulation with acenocoumarol was initiated on the second to third postoperative day. Side-effects of ticlopidine were rare and patient management with the standard dosage of this drug was easier than oral anticoagulation. From an initial group of 166 randomized patients 149 completed the trial by coronary angiography three months postoperatively. The 78 patients in the ticlopidine group showed a compliance of 85%. The average prothrombin time in the 71 patients receiving acenocoumarol was 26.9%. Detailed statistical analysis of the two study groups revealed no reason to doubt the correctness of randomization. Coronary angiography showed an average patency rate per patient of 84% with ticlopidine and of 82% with acenocoumarol. This and various other measures of graft occlusion did not reveal any substantial difference in graft patency of patients receiving ticlopidine or acenocoumarol. It is concluded that ticlopidine may well be used instead of anticoagulants forprevention of postoperative occlusion of aorto-coronary bypass graft