2,556 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
Unified Schemes for Radio-Loud Active Galactic Nuclei
The appearance of active galactic nuclei (AGN) depends so strongly on
orientation that our current classification schemes are dominated by random
pointing directions instead of more interesting physical properties. Light from
the centers of many AGN is obscured by optically thick circumnuclear matter and
in radio-loud AGN, bipolar jets emanating from the nucleus emit light that is
relativistically beamed along the jet axes. Understanding the origin and
magnitude of radiation anisotropies in AGN allows us to unify different classes
of AGN; that is, to identify each single, underlying AGN type that gives rise
to different classes through different orientations.
This review describes the unification of radio-loud AGN, which include radio
galaxies, quasars, and blazars. We describe the classification and properties
of AGN and summarize the evidence for anisotropic emission. We outline the two
most plausible unified schemes for radio-loud AGN, one linking quasars and
luminous radio galaxies and another linking BL~Lac objects and less luminous
radio galaxies. Using the formalism appropriate to samples biased by
relativistic beaming, we show the population statistics for two schemes are in
accordance with available data. We analyze the possible connections between
low- and high-luminosity radio-loud AGN. We review potential difficulties with
unification and conclude that none currently constitutes a serious problem. We
discuss likely complications to unified schemes that are suggested by realistic
physical considerations; these will be important to consider when more
comprehensive data for larger complete samples become available. We conclude
with a list of the ten questions we believe are the most pressing in this
field.Comment: 88 pages, latex file, uses aaspp.sty macro (available via ftp from
ftp://aas.org/pubs/aastex/). Accompanying 22 figures and 3 tables available
at http://itovf2.roma2.infn.it/padovani/review.html. (Abstract is abridged.)
The only change is that the revised version indicates this paper is an
invited review for PASP, in press, September 1995 issu
Macaque's Cortical Functional Connectivity Dynamics at the Onset of Propofol-Induced Anesthesia
Propofol, when administered for general anesthesia, induces oscillatory
dynamic brain states that are thought to underlie the drug's pharmacological
effects. Despite the elucidation of propofol's mechanisms of action at the
molecular level, its effects on neural circuits and overall cortical
functioning, which eventually lead to unconsciousness, are still unclear. To
identify possible mechanisms, the spatial-temporal patterns of functional
connectivity established among specialized cortical areas in anesthetized
subjects need to be described. Within this context, the present research
involved the analysis of dense sub-dural ECoG electrode array recordings from
macaques under propofol anesthetic induction. Granger causality methodology was
used to infer functional connectivity interactions in five physiological
frequency bands serially over time, every five seconds throughout the
experiment. The time-resolved networks obtained permitted us to observe the
unfolding of the anesthetic induction and compare the networks obtained under
different experimental conditions. About one minute after administering
propofol, functional connectivity started to increase for 4-5 minutes, then
decreased until the LOC was achieved. A predominant Granger causality flow from
the occipital and temporal areas towards the frontal and parietal regions was
also evidenced during the transition. During general anesthesia, the local
connectivity of the occipital lobe increased, as did the interactions between
the occipital and temporal lobes. Conversely, the functional connectivity from
the frontal and parietal lobes toward the temporal and occipital regions was
mainly impaired. The research is one of the first studies to describe the
dynamics of the functional connectivity during the transitional state that
precedes the LOC.Comment: 20 pages, 5 figure
High-energy Astrophysics and the Virtual Observatory
The Virtual Observatory (VO) will revolutionise the way we do Astronomy by
allowing easy access to all astronomical data and by making the handling and
analysis of datasets at various locations across the globe much simpler and
faster. I report here on the need for the VO and its status in Europe,
concentrating on the recently started EURO-VO project, and then give two
specific applications of VO tools to high-energy astrophysics.Comment: 12 pages, 3 figures, invited talk at the Workshop ``Multifrequency
Behaviour of High Energy Cosmic Sources'', Vulcano, Italy, May 2005, F.
Giovannelli et al., in pres
Proof Systems for Retracts in Simply Typed Lambda Calculus
Abstract. This paper concerns retracts in simply typed lambda calculus assuming βη-equality. We provide a simple tableau proof system which characterises when a type is a retract of another type and which leads to an exponential decision procedure.
Mosaico de imagens de satélite do Pantanal no ano 2000.
O Pantanal devido a sua extensão e dificuldade de acesso representa um desafio para o desenvolvimento de atividades de produção e conservação da natureza. Nesse sentido as tecnologias de Sensoriamento Remoto podem contribuir muito para o conhecimento e manejo desse ecossistema. O presente trabalho apresenta o mosaico de imagens Landsat 7 ETM do ano 2000 do Pantanal, onde ao contrário dos demais produtos dessa natureza, apresenta uma maior precisão de posicionamento em função de um extenso trabalho de campo realizado para o georreferenciamento das imagens. Esse trabalho é o resultado da parceria entre a Embrapa Pantanal e a WWF Brasil e está disponível também na homepage da Embrapa Pantanal. Esperamos com essa iniciativa estar cumprindo com nosso objetivo de levar à comunidade informações sobre o Pantanal.bitstream/item/81191/1/DOC43.pd
- …