Replay as wavefronts and theta sequences as bump oscillations in a grid cell attractor network.

Grid cells fire in sequences that represent rapid trajectories in space. During locomotion, theta sequences encode sweeps in position starting slightly behind the animal and ending ahead of it. During quiescence and slow wave sleep, bouts of synchronized activity represent long trajectories called replays, which are well-established in place cells and have been recently reported in grid cells. Theta sequences and replay are hypothesized to facilitate many cognitive functions, but their underlying mechanisms are unknown. One mechanism proposed for grid cell formation is the continuous attractor network. We demonstrate that this established architecture naturally produces theta sequences and replay as distinct consequences of modulating external input. Driving inhibitory interneurons at the theta frequency causes attractor bumps to oscillate in speed and size, which gives rise to theta sequences and phase precession, respectively. Decreasing input drive to all neurons produces traveling wavefronts of activity that are decoded as replays

Genetic algorithms applied to the scheduling of the Hubble Space Telescope

A prototype system employing a genetic algorithm (GA) has been developed to support the scheduling of the Hubble Space Telescope. A non-standard knowledge structure is used and appropriate genetic operators have been created. Several different crossover styles (random point selection, evolving points, and smart point selection) are tested and the best GA is compared with a neural network (NN) based optimizer. The smart crossover operator produces the best results and the GA system is able to evolve complete schedules using it. The GA is not as time-efficient as the NN system and the NN solutions tend to be better

Spiking neural network connectivity and its potential for temporal sensory processing and variable binding

Copyright © 2013 Wall and Glackin. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these termsPeer reviewedFinal Published versio

Role of hilar mossy cells in the CA3-dentate gyrus network during sharp wave-ripple activity in vitro

Der Gyrus dentatus (DG) des Hippokampus wird als Eingangsstation für Informationen aus dem entorhinalen Kortex betrachtet. In das DG-Netzwerk sind zwei exzitatorische Zelltypen eingebettet: Körnerzellen, die Signale von dem entorhinalen Kortex empfangen, und Hilus-Mooszellen (MCs), die Signale von Körnerzellen als auch von feedback-Projektionen von CA3-Pyramidenzellen (PCs) empfangen. Postsynaptische Ziele von MC-Projektionen umfassen DG Körnerzellen und verschiedene Interneurone in der selben und in der kontralateralen Hemisphäre des Gehirns. Die Rolle von MCs während rhythmischer Populationsaktivität, und insbesondere während Sharp-Wave / Ripple-Komplexen (SWRs), ist bisher weitgehend unerforscht. SWRs sind prominente Ereignisse im Hippocampus während des Tiefschlafs (Slow wave sleep) und des ruhigen Wachzustandes, und sie sind an der Gedächtniskonsolidierung beteiligt. In der vorliegenden Arbeit, untersuchen wir mithilfe eines in-vitro-Modells von SWRs, inwieweit Mooszellen an SWRs in CA3 beteiligt sind. Mit CA3-Feldpotential-Ableitungen und gleichzeitigen ‚cell-attached‘ Messungen von einzelnen MCs konnten wir beobachten, dass ein wesentlicher Anteil von MCs (47%) während der SWRs in das aktive neuronale Netzwerk rekrutiert werden. Darüber hinaus fanden wir in MCs SWR-assoziierte synaptische Aktivität, bei denen sowohl die exzitatorischen als auch die inhibitorischen Komponenten phasenkohärent und verzögert zur Ripple Oszillation in CA3 auftreten. Simultane Patch-clamp Messungen von CA3-Pyramidenzellen und MCs zeigten längere exzitatorische und inhibitorische Latenzzeiten bei MCs, was die Hypothese einer von CA3 ausgehenden Feedback-Rekrutierung unterstützt. Unsere Daten zeigen zusätzlich, dass das Verhältnis exzitatorischer zu inhibitorischer Aktivität in MCs höher ist als in CA3-Pyramidenzellen, wodurch die MCs mit höherer Wahrscheinlichkeit während SWRs überschwellig aktiviert werden. Schließlich zeigen wir, dass ein signifikanter Anteil (66%) der getesteten Körnerzellen SWR-assoziierte exzitatorische Signale erhalten, im Vergleich zu MCs zeitlich verzögert, was auf eine indirekte Aktivierung von Körnerzellen durch CA3 PCs über MCs hinweist. Zusammengefasst zeigen unsere Daten die aktive Beteiligung von Mooszellen an SWRs und deuten auf eine funktionelle Bedeutung als Schaltstelle für das CA3- Gyrus dentatus Netzwerk in diesem wichtigen physiologischen Netzwerkzustand hin.The dentate gyrus (DG) is considered as the hippocampal input gate for the information arriving from the entorhinal cortex. Embedded into the DG network are two excitatory cell types –granule cells (GCs), which receive inputs from the entorhinal cortex, and hilar mossy cells (MCs), which receive input from GCs and feedback projections from CA3 pyramidal cells (PCs). The postsynaptic targets of MC projections are the GCs and hilar interneurons in both ipsilateral and contralateral hemispheres of the brain. The role of MCs during rhythmic population activity, and in particular during sharp-wave/ripple complexes (SWRs), has remained largely unexplored. SWRs are prominent field events in the hippocampus during slow wave sleep and quiet wakefulness, and are involved in memory consolidation and future planning. In this study, we sought to understand whether MCs participate during CA3 SWRs using an in vitro model of SWRs. With simultaneous CA3 field potential– and cell-attached recordings from MCs, we observed that a significant fraction of MCs (47%) are recruited into the active neuronal network during SWRs. Moreover, MCs receive pronounced, compound, ripple-associated synaptic input where both excitatory and inhibitory components are phase-coherent with and delayed to the CA3 ripple. Simultaneous patch recordings from CA3 pyramidal neurons and MCs revealed longer excitatory and inhibitory latencies in MCs, supporting a feedback recruitment from CA3. Our data also show that the excitatory to inhibitory charge transfer (E/I) ratio in MCs is higher than in the CA3 PCs, making the MCs more likely to spike during SWRs. Finally, we demonstrate that a significant fraction (66%) of tested GCs receive SWR-associated excitatory inputs that are delayed compared to MCs, indicating an indirect activation of GCs by CA3 PCs via MCs. Together, our data suggest the involvement of mossy cells during SWRs and their importance as a relay for CA3-dentate gyrus networks in this important physiological network state

Efficient Implementation of the Plan Graph in STAN

STAN is a Graphplan-based planner, so-called because it uses a variety of STate ANalysis techniques to enhance its performance. STAN competed in the AIPS-98 planning competition where it compared well with the other competitors in terms of speed, finding solutions fastest to many of the problems posed. Although the domain analysis techniques STAN exploits are an important factor in its overall performance, we believe that the speed at which STAN solved the competition problems is largely due to the implementation of its plan graph. The implementation is based on two insights: that many of the graph construction operations can be implemented as bit-level logical operations on bit vectors, and that the graph should not be explicitly constructed beyond the fix point. This paper describes the implementation of STAN's plan graph and provides experimental results which demonstrate the circumstances under which advantages can be obtained from using this implementation

Performance evaluation of broadband fixed wireless system based on IEEE 802.16

Fixed Wireless Access systems operating below 11 GHz have the potential to provide broadband wireless access for non line-of-sight operation. In this paper the performance of a typical broadband fixed wireless system based on the IEEE 802.16-2004 specifications is determined. A scenario for business applications with outdoor customer premises equipment is investigated in the 3.5 GHz frequency band. Different path loss models and terrain types are considered. Coverage and throughput in a sector are determined for this business scenario

Rapid, parallel path planning by propagating wavefronts of spiking neural activity

Efficient path planning and navigation is critical for animals, robotics, logistics and transportation. We study a model in which spatial navigation problems can rapidly be solved in the brain by parallel mental exploration of alternative routes using propagating waves of neural activity. A wave of spiking activity propagates through a hippocampus-like network, altering the synaptic connectivity. The resulting vector field of synaptic change then guides a simulated animal to the appropriate selected target locations. We demonstrate that the navigation problem can be solved using realistic, local synaptic plasticity rules during a single passage of a wavefront. Our model can find optimal solutions for competing possible targets or learn and navigate in multiple environments. The model provides a hypothesis on the possible computational mechanisms for optimal path planning in the brain, at the same time it is useful for neuromorphic implementations, where the parallelism of information processing proposed here can fully be harnessed in hardware