24,146 research outputs found
Characterization of Large Scale Functional Brain Networks During Ketamine-Medetomidine Anesthetic Induction
Several experiments evidence that specialized brain regions functionally
interact and reveal that the brain processes and integrates information in a
specific and structured manner. Networks can be used to model brain functional
activities constituting a way to characterize and quantify this structured form
of organization. Reports state that different physiological states or even
diseases that affect the central nervous system may be associated to
alterations on those networks, that might reflect in graphs of different
architectures. However, the relation of their structure to different states or
conditions of the organism is not well comprehended. Thus, experiments that
involve the estimation of functional neural networks of subjects exposed to
different controlled conditions are of great relevance. Within this context,
this research has sought to model large scale functional brain networks during
an anesthetic induction process. The experiment was based on intra-cranial
recordings of neural activities of an old world macaque of the species Macaca
fuscata. Neural activity was recorded during a Ketamine-Medetomidine anesthetic
induction process. Networks were serially estimated in time intervals of five
seconds. Changes were observed in various networks properties within about one
and a half minutes after the administration of the anesthetics. These changes
reveal the occurrence of a transition on the networks architecture. During
general anesthesia a reduction in the functional connectivity and network
integration capabilities were verified in both local and global levels. It was
also observed that the brain shifted to a highly specific and dynamic state.
The results bring empirical evidence and report the relation of the induced
state of anesthesia to properties of functional networks, thus, they contribute
for the elucidation of some new aspects of neural correlates of consciousness.Comment: 28 pages , 9 figures, 7 tables; - English errors were corrected;
Figures 1,3,4,5,6,8 and 9 were replaced by (exact the same)figures of higher
resolution; Three(3) references were added on the introduction sectio
Characterization of the Community Structure of Large Scale Functional Brain Networks During Ketamine-Medetomidine Anesthetic Induction
One of the central questions in neuroscience is to understand the way
communication is organized in the brain, trying to comprehend how cognitive
capacities or physiological states of the organism are potentially related to
brain activities involving interactions of several brain areas. One important
characteristic of the functional brain networks is that they are modularly
structured, being this modular architecture regarded to account for a series of
properties and functional dynamics. In the neurobiological context, communities
may indicate brain regions that are involved in one same activity, representing
neural segregated processes. Several studies have demonstrated the modular
character of organization of brain activities. However, empirical evidences
regarding to its dynamics and relation to different levels of consciousness
have not been reported yet. Within this context, this research sought to
characterize the community structure of functional brain networks during an
anesthetic induction process. The experiment was based on intra-cranial
recordings of neural activities of an old world macaque of the species Macaca
fuscata during a Ketamine-Medetomidine anesthetic induction process. Networks
were serially estimated in time intervals of five seconds. Changes were
observed within about one and a half minutes after the administration of the
anesthetics, revealing the occurrence of a transition on the community
structure. The awake state was characterized by the presence of large clusters
involving frontal and parietal regions, while the anesthetized state by the
presence of communities in the primary visual and motor cortices, being the
areas of the secondary associative cortex most affected. The results report the
influence of general anesthesia on the structure of functional clusters,
contributing for understanding some new aspects of neural correlates of
consciousness.Comment: 24 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1604.0000
Structure and Dynamics of Brain Lobes Functional Networks at the Onset of Anesthesia Induced Loss of Consciousness
Anesthetic agents are neurotropic drugs able to induce dramatic alterations
in the thalamo-cortical system, promoting a drastic reduction in awareness and
level of consciousness. There is experimental evidence that general anesthesia
impacts large scale functional networks leading to alterations in the brain
state. However, the way anesthetics affect the structure assumed by functional
connectivity in different brain regions have not been reported yet. Within this
context, the present study has sought to characterize the functional brain
networks respective to the frontal, parietal, temporal and occipital lobes. In
this experiment, electro-physiological neural activity was recorded through the
use of a dense ECoG-electrode array positioned directly over the cortical
surface of an old world monkey of the species Macaca fuscata. Networks were
serially estimated over time at each five seconds, while the animal model was
under controlled experimental conditions of an anesthetic induction process. In
each one of the four cortical brain lobes, prominent alterations on distinct
properties of the networks evidenced a transition in the networks architecture,
which occurred within about one and a half minutes after the administration of
the anesthetics. The characterization of functional brain networks performed in
this study represents important experimental evidence and brings new knowledge
towards the understanding of neural correlates of consciousness in terms of the
structure and properties of the functional brain networks.Comment: 41 pages; 30 figures; 30 tables. arXiv admin note: substantial text
overlap with arXiv:1604.0000
Democracy and social utopias : a study about Albrecht Wellmer and Axel Honneth
This work intends to analysis the philosophy of history and to discuss the consequences of this death to the Critical Theory. The concept of reason and the devices of democracy and human rights are discussed in a revision of the historical debate about the end of history operates the life in the interior of the modern society, especially about the intellectual condition at the information society
Locality-preserving allocations Problems and coloured Bin Packing
We study the following problem, introduced by Chung et al. in 2006. We are
given, online or offline, a set of coloured items of different sizes, and wish
to pack them into bins of equal size so that we use few bins in total (at most
times optimal), and that the items of each colour span few bins (at
most times optimal). We call such allocations -approximate. As usual in bin packing problems, we allow additive
constants and consider as the asymptotic performance ratios.
We prove that for \eps>0, if we desire small , no scheme can beat
(1+\eps, \Omega(1/\eps))-approximate allocations and similarly as we desire
small , no scheme can beat (1.69103, 1+\eps)-approximate allocations.
We give offline schemes that come very close to achieving these lower bounds.
For the online case, we prove that no scheme can even achieve
-approximate allocations. However, a small restriction on item
sizes permits a simple online scheme that computes (2+\eps, 1.7)-approximate
allocations
Time-dependent quantum transport and power-law decay of the transient current in a nano-relay and nano-oscillator
Time-dependent nonequilibrium Green's functions are used to study electron
transport properties in a device consisting of two linear chain leads and a
time-dependent interleads coupling that is switched on non-adiabatically. We
derive a numerically exact expression for the particle current and examine its
characteristics as it evolves in time from the transient regime to the
long-time steady-state regime. We find that just after switch-on the current
initially overshoots the expected long-time steady-state value, oscillates and
decays as a power law, and eventually settles to a steady-state value
consistent with the value calculated using the Landauer formula. The power-law
parameters depend on the values of the applied bias voltage, the strength of
the couplings, and the speed of the switch-on. In particular, the oscillating
transient current decays away longer for lower bias voltages. Furthermore, the
power-law decay nature of the current suggests an equivalent series
resistor-inductor-capacitor circuit wherein all of the components have
time-dependent properties. Such dynamical resistive, inductive, and capacitive
influences are generic in nano-circuites where dynamical switches are
incorporated. We also examine the characteristics of the dynamical current in a
nano-oscillator modeled by introducing a sinusoidally modulated interleads
coupling between the two leads. We find that the current does not strictly
follow the sinusoidal form of the coupling. In particular, the maximum current
does not occur during times when the leads are exactly aligned. Instead, the
times when the maximum current occurs depend on the values of the bias
potential, nearest-neighbor coupling, and the interleads coupling.Comment: version accepted for publication in JA
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