Dynamical complexity in the C.elegans neural network

We model the neuronal circuit of the C.elegans soil worm in terms of a Hindmarsh-Rose system of ordinary differential equa- tions, dividing its circuit into six communities which are determined via the Walktrap and Louvain methods. Using the numerical solution of these equations, we analyze important measures of dynamical com- plexity, namely synchronicity, the largest Lyapunov exponent, and the ?AR auto-regressive integrated information theory measure. We show that ?AR provides a useful measure of the information contained in the C.elegans brain dynamic network. Our analysis reveals that the C.elegans brain dynamic network generates more information than the sum of its constituent parts, and that attains higher levels of integrated information for couplings for which either all its communities are highly synchronized, or there is a mixed state of highly synchronized and de- synchronized communities

Spike timing-dependent plasticity induces non-trivial topology in the brain.

We study the capacity of Hodgkin-Huxley neuron in a network to change temporarily or permanently their connections and behavior, the so called spike timing-dependent plasticity (STDP), as a function of their synchronous behavior. We consider STDP of excitatory and inhibitory synapses driven by Hebbian rules. We show that the final state of networks evolved by a STDP depend on the initial network configuration. Specifically, an initial all-to-all topology evolves to a complex topology. Moreover, external perturbations can induce co-existence of clusters, those whose neurons are synchronous and those whose neurons are desynchronous. This work reveals that STDP based on Hebbian rules leads to a change in the direction of the synapses between high and low frequency neurons, and therefore, Hebbian learning can be explained in terms of preferential attachment between these two diverse communities of neurons, those with low-frequency spiking neurons, and those with higher-frequency spiking neurons

Self-sustained activity of low firing rate in balanced networks

Self-sustained activity in the brain is observed in the absence of external stimuli and contributes to signal propagation, neural coding, and dynamic stability. It also plays an important role in cognitive processes. In this work, by means of studying intracellular recordings from CA1 neurons in rats and results from numerical simulations, we demonstrate that self-sustained activity presents high variability of patterns, such as low neural firing rates and activity in the form of small-bursts in distinct neurons. In our numerical simulations, we consider random networks composed of coupled, adaptive exponential integrate-and-fire neurons. The neural dynamics in the random networks simulates regular spiking (excitatory) and fast spiking (inhibitory) neurons. We show that both the connection probability and network size are fundamental properties that give rise to self-sustained activity in qualitative agreement with our experimental results. Finally, we provide a more detailed description of self-sustained activity in terms of lifetime distributions, synaptic conductances, and synaptic currents

Does Astronomical and Geographical Information of Plutarch's de Facie Describe a Trip beyond the North Atlantic Ocean?

In Plutarch's book On the Apparent Face in the Orb of the Moon, the interlocutors develop a dialogue about a trip to the "great continent" beyond the North Atlantic Ocean. By applying modern scientific data, the present reappraisal of the astronomical and geographical elements within this dialogue has produced a novel interpretation of the date and place of the meeting and a journey to the northern Atlantic Ocean. A described solar eclipse is dated to AD 75, making use of the National Aeronautics and Space Administration (NASA)/Espenak/Meeus list, as well as historical information. The described peculiar, recurrent trips take place every 30 years (when the planet Saturn reaches the Taurus constellation) from the Mediterranean Sea to the Cronian Open Sea, which is identified with northern Atlantic Ocean coasts. It has been suggested that the last mission had returned homeland in April AD 56. The information provided concerns, distances between coastal sites and islands, duration of sea paths in days, and the reported setting and size between the destination place and its gulf with regards to Azov (in Crimea) and the Caspian Sea. Implications of sea currents and the coastal geomorphology of those lands are given. Following strictly the Gulf Stream current, as well as other known sea currents in the northern Atlantic Ocean, and introducing estimated speed for the ship, the geographical location of destination of the Greek settlers is proposedly identified with St. Lawrence Gulf and Newfoundland island. Other unnamed islands mentioned in this dialogue are identified with Norway's islands, Azores, Iceland, Greenland, and Baffin islands. It has been shown that the journey is made with good knowledge of sea currents but by using bright stars and stellar configurations as astronomical nightscape markers that determine the exact orientation of the sailing toward the Iberian Peninsula and back to the eastern Mediterranean, making the current working hypothesis a plausible event. © 2018 Coastal Education and Research Foundation, Inc