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Spatial Embedding and Wiring Cost Constrain the Functional Layout of the Cortical Network of Rodents and Primates
(2016-07-21) Horvát, Szabolcs; Gămănuț, Răzvan; Ercsey-Ravasz, Mária; Magrou, Loïc; Gămănuț, Bianca; Van Essen, David C.; Burkhalter, Andreas; Knoblauch, Kenneth; Toroczkai, Zoltán; Kennedy, Henry; Department of Computer Science
Mammals show a wide range of brain sizes, reflecting adaptation to diverse habitats. Comparing interareal cortical networks across brains of different sizes and mammalian orders provides robust information on evolutionarily preserved features and species-specific processing modalities. However, these networks are spatially embedded, directed, and weighted, making comparisons challenging. Using tract tracing data from macaque and mouse, we show the existence of a general organizational principle based on an exponential distance rule (EDR) and cortical geometry, enabling network comparisons within the same model framework. These comparisons reveal the existence of network invariants between mouse and macaque, exemplified in graph motif profiles and connection similarity indices, but also significant differences, such as fractionally smaller and much weaker long-distance connections in the macaque than in mouse. The latter lends credence to the prediction that long-distance cortico-cortical connections could be very weak in the much-expanded human cortex, implying an increased susceptibility to disconnection syndromes such as Alzheimer disease and schizophrenia. Finally, our data from tracer experiments involving only gray matter connections in the primary visual areas of both species show that an EDR holds at local scales as well (within 1.5 mm), supporting the hypothesis that it is a universally valid property across all scales and, possibly, across the mammalian class.
Verk
Quark number scaling in fluid dynamics and hadronization via quarkyonic matter
(2012) Csernai, L. P.; Cheng, Y.; Horvat, Sz; Mishustin, I.; Zschocke, S.; Department of Computer Science
NCQ scaling of elliptic flow is studied in a non-equilibrium hadronization and freeze-out model from ideal, deconfined and chirally symmetric Quark Gluon Plasma (QGP), to final non-interacting hadrons. In this transition the quarks gain constituent quark mass while the background Bag-field breaks up. The constituent quarks then recombine into simplified hadron states, while chemical, thermal and flow equilibrium break down. Then the resulting temperatures and flow velocities of baryons and mesons will be different. In a simplified model, we reproduce the constituent quark number scaling.
Verk
A spatially explicit model for tropical tree diversity patterns
(2010-08) Horvát, Szabolcs; Derzsi, A.; Néda, Z.; Balog, A.; Department of Computer Science
A simple two-parameter model resembling the classical voter model is introduced to describe macroecological properties of tropical tree communities. The parameters of the model characterize the speciation- and global-dispersion rates. Monte Carlo type computer simulations are performed on the model, investigating species abundances and the spatial distribution of individuals and species. Simulation results are critically compared with the experimental data obtained from a tree census on a 50 hectare area of the Barro Colorado Island (BCI), Panama. Fitting to only two observable quantities from the BCI data (total species number and the slope of the log-log species-area curve at the maximal area), it is possible to reproduce the full species-area curve, the relative species abundance distribution, and a more realistic spatial distribution of species.
Verk
Unexpected synchronization
(2009) Horvát, Szabolcs; Horváth, E. Ágnes; Máté, Gabriell; Káptalan, Erna; Néda, Zoltán; Department of Computer Science
An ensemble of oscillators capable of a highly nontrivial synchronization is investigated. The oscillators are stochastic units which can emit a signal and detect signals emitted by others. They have two operational modes characterized by two different oscillation periods. Switching between the modes is governed by a simple rule: the average output intensity is kept around a prescribed threshold. This simple dynamical rule realizes the coupling of the units and leads to a complex collective behaviour. Computer simulations proved that for a given interval of the threshold parameter, partial synchronization of the units occurs. The appearance and disappearance of this synchronization as a function of the threshold parameter indicates a phase-transition type behaviour.

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