4,218 research outputs found
The Contribution of Thalamocortical Core and Matrix Pathways to Sleep Spindles.
Sleep spindles arise from the interaction of thalamic and cortical neurons. Neurons in the thalamic reticular nucleus (TRN) inhibit thalamocortical neurons, which in turn excite the TRN and cortical neurons. A fundamental principle of anatomical organization of the thalamocortical projections is the presence of two pathways: the diffuse matrix pathway and the spatially selective core pathway. Cortical layers are differentially targeted by these two pathways with matrix projections synapsing in superficial layers and core projections impinging on middle layers. Based on this anatomical observation, we propose that spindles can be classified into two classes, those arising from the core pathway and those arising from the matrix pathway, although this does not exclude the fact that some spindles might combine both pathways at the same time. We find evidence for this hypothesis in EEG/MEG studies, intracranial recordings, and computational models that incorporate this difference. This distinction will prove useful in accounting for the multiple functions attributed to spindles, in that spindles of different types might act on local and widespread spatial scales. Because spindle mechanisms are often hijacked in epilepsy and schizophrenia, the classification proposed in this review might provide valuable information in defining which pathways have gone awry in these neurological disorders
Delay Differential Analysis of Seizures in Multichannel Electrocorticography Data
High-density electrocorticogram (ECoG) electrodes are capable of recording neurophysiological data with high temporal resolution with wide spatial coverage. These recordings are a window to understanding how the human brain processes information and subsequently behaves in healthy and pathologic states. Here, we describe and implement delay differential analysis (DDA) for the characterization of ECoG data obtained from human patients with intractable epilepsy. DDA is a time-domain analysis framework based on embedding theory in nonlinear dynamics that reveals the nonlinear invariant properties of an unknown dynamical system. The DDA embedding serves as a low-dimensional nonlinear dynamical basis onto which the data are mapped. This greatly reduces the risk of overfitting and improves the method's ability to fit classes of data. Since the basis is built on the dynamical structure of the data, preprocessing of the data (e.g., filtering) is not necessary. We performed a large-scale search for a DDA model that best fit ECoG recordings using a genetic algorithm to qualitatively discriminate between different cortical states and epileptic events for a set of 13 patients. A single DDA model with only three polynomial terms was identified. Singular value decomposition across the feature space of the model revealed both global and local dynamics that could differentiate electrographic and electroclinical seizures and provided insights into highly localized seizure onsets and diffuse seizure terminations. Other common ECoG features such as interictal periods, artifacts, and exogenous stimuli were also analyzed with DDA. This novel framework for signal processing of seizure information demonstrates an ability to reveal unique characteristics of the underlying dynamics of the seizure and may be useful in better understanding, detecting, and maybe even predicting seizures
The Deliberate Speed of the Tar Heel State: North Carolina’s Efforts to Resist School Desegregation, 1954-1966
The Deliberate Speed of the Tar Heel State offers readers an examination of the efforts undertaken by North Carolina in hope of resisting public school desegregation between the Brown v. Board decisions of 1954, 1955, and 1966. It will examine the state’s use of a series of legal, legislative maneuvers, The Pupil Assignment Act of 1955 and the Pearsall Plan of 1956, which attempted to show definitive progress to the federal government while simultaneously ensuring the segregated public school system remained intact. By examining the efforts of individuals such as William Umstead, Luther Hodges, Terry Sanford, Thomas Pearsall, and others, this thesis will analyze how North Carolina attempted to use more “moderate” means of resisting federally mandated school desegregation and whether the state was successful in their efforts
Think about your heart: The Effects of Cognitive Dissonance on cardiovascular functioning
Cognitive dissonance (CD) occurs when an individual’s attitudes are inconsistent with his/her behavior, and can result in emotional distress. Individuals may regulate and reduce this emotional distress by changing their attitudes to match behaviors. Individuals with higher resting heart rate variability (HRV), a marker of overall health, have been shown to better regulate and control negative emotions. Thus, the following investigation sought to examine the relationship between cognitive dissonance, emotional distress, HRV, and other physiological indicators of health. HRV data were collected using an electrocardiogram (EKG) from 81 participants during a baseline evaluation, randomized CD induction of high or low choice, and recovery. In the low choice group, individuals were instructed to write a counter-attitudinal essay and therefore, attribute feelings of dissonance to experimenter demands. In the high choice condition, while urging them to comply, individuals were told that it is optional to write the counter-attitudinal essay; here, participants are motivated to change their attitudes to match behavior due to their compliance. I hypothesized that (1) The high choice group would be more likely to change their attitudes following the essay in comparison to the low choice group; (2) baseline HRV would predict attitude change following dissonance, especially in the high choice condition; (3) measures of arousal (e.g. self-reported mood, blood pressure) would be elevated in the high choice group in comparison to the low choice group. Results partially supported these hypotheses, showing that resting HRV does predict attitude change in both experimental conditions. Implication and future directions are discussed.Department of Psychology Summer Research FellowshipNo embargoAcademic Major: Psycholog
Neural Correlates of Auditory Perceptual Awareness and Release from Informational Masking Recorded Directly from Human Cortex: A Case Study.
In complex acoustic environments, even salient supra-threshold sounds sometimes go unperceived, a phenomenon known as informational masking. The neural basis of informational masking (and its release) has not been well-characterized, particularly outside auditory cortex. We combined electrocorticography in a neurosurgical patient undergoing invasive epilepsy monitoring with trial-by-trial perceptual reports of isochronous target-tone streams embedded in random multi-tone maskers. Awareness of such masker-embedded target streams was associated with a focal negativity between 100 and 200 ms and high-gamma activity (HGA) between 50 and 250 ms (both in auditory cortex on the posterolateral superior temporal gyrus) as well as a broad P3b-like potential (between ~300 and 600 ms) with generators in ventrolateral frontal and lateral temporal cortex. Unperceived target tones elicited drastically reduced versions of such responses, if at all. While it remains unclear whether these responses reflect conscious perception, itself, as opposed to pre- or post-perceptual processing, the results suggest that conscious perception of target sounds in complex listening environments may engage diverse neural mechanisms in distributed brain areas
Optimization of grazing incidence mirrors and its application to surveying X-ray telescopes
Grazing incidence mirrors for X-ray astronomy are usually designed in the
parabola-hyperbola (Wolter I) configuration. This design allows for optimal
images on-axis, which however degrade rapidly with the off-axis angle. Mirror
surfaces described by polynomia (with terms higher than order two), have been
put forward to improve the performances over the field of view. Here we present
a refined procedure aimed at optimizing wide-field grazing incidence telescopes
for X-ray astronomy. We improve the angular resolution over existing
(wide-field) designs by ~ 20%. We further consider the corrections for the
different plate scale and focal plane curvature of the mirror shells, which
sharpen by another ~ 20% the image quality. This results in a factor of ~ 2
reduction in the observing time needed to achieve the same sensitivity over
existing wide-field designs and of ~ 5 over Wolter I telescopes. We demonstrate
that such wide-field X-ray telescopes are highly advantageous for deep surveys
of the X-ray sky.Comment: 8 pages 4 figures. Accepted for publication on A&A (macro included
An adaptive-binning method for generating constant-uncertainty/constant-significance light curves with Fermi-LAT data
We present a method enabling the creation of
constant-uncertainty/constant-significance light curves with the data of the
Fermi-Large Area Telescope (LAT). The adaptive-binning method enables more
information to be encapsulated within the light curve than with the
fixed-binning method. Although primarily developed for blazar studies, it can
be applied to any sources. This method allows the starting and ending times of
each interval to be calculated in a simple and quick way during a first step.
The reported mean flux and spectral index (assuming the spectrum is a power-law
distribution) in the interval are calculated via the standard LAT analysis
during a second step. The absence of major caveats associated with this method
has been established by means of Monte-Carlo simulations. We present the
performance of this method in determining duty cycles as well as power-density
spectra relative to the traditional fixed-binning method.Comment: 17 pages, 13 figures, 5 tables. Submitted to A&
Chemerin15 inhibits neutrophil-mediated vascular inflammation and myocardial ischemia-reperfusion injury through ChemR23
Neutrophil activation and adhesion must be tightly controlled to prevent complications associated with excessive inflammatory responses. The role of the anti-inflammatory peptide chemerin15 (C15) and the receptor ChemR23 in neutrophil physiology is unknown. Here, we report that ChemR23 is expressed in neutrophil granules and rapidly upregulated upon neutrophil activation. C15 inhibits integrin activation and clustering, reducing neutrophil adhesion and chemotaxis in vitro. In the inflamed microvasculature, C15 rapidly modulates neutrophil physiology inducing adherent cell detachment from the inflamed endothelium, while reducing neutrophil recruitment and heart damage in a murine myocardial infarction model. These effects are mediated through ChemR23. We identify the C15/ChemR23 pathway as a new regulator and thus therapeutic target in neutrophil-driven pathologies
Avalanche analysis from multi-electrode ensemble recordings in cat, monkey and human cerebral cortex during wakefulness and sleep
Self-organized critical states are found in many natural systems, from
earthquakes to forest fires, they have also been observed in neural systems,
particularly, in neuronal cultures. However, the presence of critical states in
the awake brain remains controversial. Here, we compared avalanche analyses
performed on different in vivo preparations during wakefulness, slow-wave sleep
and REM sleep, using high-density electrode arrays in cat motor cortex (96
electrodes), monkey motor cortex and premotor cortex and human temporal cortex
(96 electrodes) in epileptic patients. In neuronal avalanches defined from
units (up to 160 single units), the size of avalanches never clearly scaled as
power-law, but rather scaled exponentially or displayed intermediate scaling.
We also analyzed the dynamics of local field potentials (LFPs) and in
particular LFP negative peaks (nLFPs) among the different electrodes (up to 96
sites in temporal cortex or up to 128 sites in adjacent motor and pre-motor
cortices). In this case, the avalanches defined from nLFPs displayed power-law
scaling in double log representations, as reported previously in monkey.
However, avalanche defined as positive LFP (pLFP) peaks, which are less
directly related to neuronal firing, also displayed apparent power-law scaling.
Closer examination of this scaling using more reliable cumulative distribution
functions (CDF) and other rigorous statistical measures, did not confirm
power-law scaling. The same pattern was seen for cats, monkey and human, as
well as for different brain states of wakefulness and sleep. We also tested
other alternative distributions. Multiple exponential fitting yielded optimal
fits of the avalanche dynamics with bi-exponential distributions. Collectively,
these results show no clear evidence for power-law scaling or self-organized
critical states in the awake and sleeping brain of mammals, from cat to man.Comment: In press in: Frontiers in Physiology, 2012, special issue "Critical
Brain Dynamics" (Edited by He BY, Daffertshofer A, Boonstra TW); 33 pages, 13
figures. 3 table
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