27,708 research outputs found
The Importance of Forgetting: Limiting Memory Improves Recovery of Topological Characteristics from Neural Data
We develop of a line of work initiated by Curto and Itskov towards
understanding the amount of information contained in the spike trains of
hippocampal place cells via topology considerations. Previously, it was
established that simply knowing which groups of place cells fire together in an
animal's hippocampus is sufficient to extract the global topology of the
animal's physical environment. We model a system where collections of place
cells group and ungroup according to short-term plasticity rules. In
particular, we obtain the surprising result that in experiments with spurious
firing, the accuracy of the extracted topological information decreases with
the persistence (beyond a certain regime) of the cell groups. This suggests
that synaptic transience, or forgetting, is a mechanism by which the brain
counteracts the effects of spurious place cell activity
Perspective: network-guided pattern formation of neural dynamics
The understanding of neural activity patterns is fundamentally linked to an
understanding of how the brain's network architecture shapes dynamical
processes. Established approaches rely mostly on deviations of a given network
from certain classes of random graphs. Hypotheses about the supposed role of
prominent topological features (for instance, the roles of modularity, network
motifs, or hierarchical network organization) are derived from these
deviations. An alternative strategy could be to study deviations of network
architectures from regular graphs (rings, lattices) and consider the
implications of such deviations for self-organized dynamic patterns on the
network. Following this strategy, we draw on the theory of spatiotemporal
pattern formation and propose a novel perspective for analyzing dynamics on
networks, by evaluating how the self-organized dynamics are confined by network
architecture to a small set of permissible collective states. In particular, we
discuss the role of prominent topological features of brain connectivity, such
as hubs, modules and hierarchy, in shaping activity patterns. We illustrate the
notion of network-guided pattern formation with numerical simulations and
outline how it can facilitate the understanding of neural dynamics
Temporal Evolution of the Magnetic Topology of the NOAA Active Region 11158
We studied the temporal evolution of the magnetic topology of the active
region (AR) 11158 based on the reconstructed three-dimensional magnetic fields
in the corona. The \nlfff\ extrapolation method was applied to the 12 minutes
cadence data obtained with the \hmi\ (HMI) onboard the \sdo\ (SDO) during five
days. By calculating the squashing degree factor Q in the volume, the derived
quasi-separatrix layers (QSLs) show that this AR has an overall topology,
resulting from a magnetic quadrupole, including an hyperbolic flux tube (HFT)
configuration which is relatively stable at the time scale of the flare ( hours). A strong QSL, which corresponds to some highly sheared arcades
that might be related to the formation of a flux rope, is prominent just before
the M6.6 and X2.2 flares, respectively. These facts indicate the close
relationship between the strong QSL and the high flare productivity of AR
11158. In addition, with a close inspection of the topology, we found a
small-scale HFT which has an inverse tear-drop structure above the
aforementioned QSL before the X2.2 flare. It indicates the existence of
magnetic flux rope at this place. Even though a global configuration (HFT) is
recognized in this AR, it turns out that the large-scale HFT only plays a
secondary role during the eruption. In final, we dismiss a trigger based on the
breakout model and highlight the central role of the flux rope in the related
eruption.Comment: Accepted by Ap
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