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Spontaneous Fluctuations in Posterior alpha-Band EEG Activity Reflect Variability in Excitability of Human Visual Areas.: Cereb Cortex (18 December 2007)Neural activity fluctuates dynamically with time, and these changes have been reported to be of behavioral significance, despite occurring spontaneously. Through electroencepha lography (EEG), fluctuations in alpha-band (8-14 Hz) activity have been identified over posterior sites that covary on a trial-by-trial basis with whether an upcoming visual stimulus will be detected or not. These fluctuations are thought to index the momentary state of visual cortex excitability. Here, we tested this hypothesis by directly exciting human visual cortex via transcranial magnetic stimulation (TMS) to induce illusory visual percepts (phosphenes) in blindfolded participants, while simultaneously recording EEG. We found that identical TMS-stimuli evoked a percept (P-yes) or not (P-no) depending on prestimulus alpha-activity . Low prestimulus alpha-band power resulted in TMS reliably inducing phosphenes (P-yes trials), whereas high prestimulus alpha-values led the same TMS-stimuli failing to evoke a visual percept (P-no trials). Additional analyses indicated that the perceptually relevant fluctuations in alpha-activity /visual cortex excitability were spatially specific and occurred on a subsecond time scale in a recurrent pattern. Our data directly link momentary levels of posterior alpha-band activity to distinct states of visual cortex excitability, and suggest that their spontaneous fluctuation constitutes a visual operation mode that is activated automatically even without retinal input.

Source: Cereb Cortex (18 December 2007)
Posterior ? activity is not phase-reset by visual stimuli: Proceedings of the National Academy of Sciences of the United States of America, Vol. 103, No. 8. (21 February 2006), pp. 2948-2952.10.1 073/pnas.05057 85103 There is currently a debate as to whether event-related potentials and fields measured by using electroencepha lography or magnetoencepha lography are generated by ongoing oscillatory activity becoming phase-reset in response to a given stimulus. We performed a magnetoencepha lography study measuring brain activity in response to visual stimuli. Using a measure termed the phase-preserva tion index we investigated the phase of oscillatory ? activity (8?13 Hz) before and after the stimulus. We found that in single trials the ? oscillations after visual stimuli preserve their phase relationship with respect to the phase before the stimuli. This finding argues against phase-resettin g of ongoing oscillations as being responsible for visually evoked responses. The event-related field can be explained primarily by stimulus-locke d activity in the ? band that is absent before the stimulus. These findings suggest that different neuronal events are responsible for generating the ongoing oscillations and the visually evoked responses.

Source: Proceedings of the National Academy of Sciences of the United States of America, Vol. 103, No. 8. (21 February 2006), pp. 2948-2952.
Long-range temporal correlations in alpha and beta oscillations: effect of arousal level and test-retest reliability: Clinical Neurophysiolog y, Vol. 115, No. 8. (August 2004), pp. 1896-1908.Obje ctive: The aim of the present study was to evaluate test-retest reliability and condition sensitivity of long-range temporal correlations in the amplitude dynamics of electroencepha lographic alpha and beta oscillations.M ethods: Twelve normal subjects were measured two times with a test-retest interval of several days. Open- and closed-eyes conditions were used, representing different levels of arousal. The amplitude of the alpha and beta oscillations was extracted with bandpass filtering and the Hilbert transform. The long-range temporal correlations were quantified with detrended fluctuation analysis.Resul ts: The amplitude dynamics of the alpha and beta oscillations demonstrated power-law long-range temporal correlations lasting for tens of seconds. These correlations were degraded in the open- compared to the closed-eyes condition. Test-retest statistics demonstrated that the long-range temporal correlations had significant reliability, which was greatest in the closed-eyes condition.Conc lusions: The presence of long-range temporal correlations indicates that the amplitude of neuronal oscillations at a given time is dependent on the amplitude at times as remote in the past as tens of seconds. The reliability of long-range temporal correlations suggests that the mechanisms generating the amplitude fluctuations are not perturbed over several days. The systematic changes in the scaling exponents at different levels of arousal indicate that these changes occur on many time scales (5-80 s) as a result of modifications in the intrinsic dynamics of the neuronal oscillations.S ignificance: This study demonstrates that the dynamics of spontaneous neuronal oscillations possess long-range temporal correlations with properties suitable for functional and clinical studies.

Source: Clinical Neurophysiology, Vol. 115, No. 8. (August 2004), pp. 1896-1908.
Exercise preconditionin g reduces brain damage and inhibits TNF-alpha receptor expression after hypoxia/reoxyg enation: an in vivo and in vitro study.: Curr Neurovasc Res, Vol. 3, No. 4. (November 2006), pp. 263-271.Exerci se reduces ischemia and reperfusion injury in rat stroke models. We investigated whether gradual increases in tumor necrosis factor-alpha (TNF-alpha) reported during exercise down-regulates expression of TNF-alpha receptors I and II (TNFRI and II) in stroke, leading to reduced brain damage. Adult male Sprague Dawley rats were subjected to 30 minutes of exercise on a treadmill each day for 3 weeks. Then, stroke was induced by a 2-hour middle cerebral artery (MCA) occlusion using an intra-luminal filament. Expressions of TNFRI and II mRNA in the brain were detected using a real-time reverse transcriptase- polymerase chain reaction (RT-PCR). Protein expressions of TNFRI and II were determined by enzyme-linked immunoabsorban t assay (ELISA) in serum and brain homogenates. Spatial distribution of TNF-alpha receptors in brain regions was determined with immunocytochem istry. In human umbilical vein endothelial cells (HUVEC), we addressed the causal effect of TNF-alpha pretreatment on TNF I and II expression using ELISA and real-time PCR. In exercised rats after stroke, brain infarct was significantly (p

Source: Curr Neurovasc Res, Vol. 3, No. 4. (November 2006), pp. 263-271.
Stroke upregulates TNFalpha transport across the blood-brain barrier.: Exp Neurol, Vol. 198, No. 1. (March 2006), pp. 222-233.To determine how cytokine transport systems at the blood-brain barrier (BBB) participate in stroke progression and recovery, we generated a mouse model of transient middle cerebral artery occlusion (tMCAO). After 1 h of occlusion followed by nearly complete reperfusion, the neurological deficits lasted more than a week as shown by several behavioral tests. Despite the prominent infarct area indicated by reduced cerebral perfusion and confirmed by vital staining, the volume of distribution of (131)I-albumin in various brain regions was not significantly altered over time (12 h to 14 days). In sharp contrast, the blood-to-brain permeation of 125I-TNFalpha was significantly increased 5 days after tMCAO. Furthermore, excess unlabeled TNFalpha abolished this enhanced 125I-TNFalpha uptake. Thus, not only did the known saturable transport system for TNFalpha persist, but it functioned at a higher capacity in tMCAO mice. Upregulation of TNFR1 and TNFR2 partially explains the increased transport, as mRNA for both receptors showed the most pronounced increase (15-fold and 30-fold, respectively) in the ischemic hemisphere 5-7 days after tMCAO. However, even in the hemisphere contralateral to the ischemia induced by stroke, there was increased TNFalpha transport. The bilateral increase in 125I-TNFalpha entry from blood to brain suggests that TNFalpha trafficking in cerebral endothelial cells is influenced by global mediators in addition to the transporting receptors. Given the known multiple modulatory effects of TNFalpha after stroke, the results indicate that the TNFalpha transport system at the BBB facilitates neuroplasticit y and plays an important role in stroke recovery.

Source: Exp Neurol, Vol. 198, No. 1. (March 2006), pp. 222-233.
Optimized Color Sampling for Robust Matting: Computer Vision and Pattern Recognition, 2007. CVPR '07. IEEE Conference on (2007), pp. 1-8.Image matting is the problem of determining for each pixel in an image whether it is foreground, background, or the mixing parameter, "alpha", for those pixels that are a mixture of foreground and background. Matting is inherently an ill-posed problem. Previous matting approaches either use naive color sampling methods to estimate foreground and background colors for unknown pixels, or use propagation-ba sed methods to avoid color sampling under weak assumptions about image statistics. We argue that neither method itself is enough to generate good results for complex natural images. We analyze the weaknesses of previous matting approaches, and propose a new robust matting algorithm. In our approach we also sample foreground and background colors for unknown pixels, but more importantly, analyze the confidence of these samples. Only high confidence samples are chosen to contribute to the matting energy function which is minimized by a Random Walk. The energy function we define also contains a neighborhood term to enforce the smoothness of the matte. To validate the approach, we present an extensive and quantitative comparison between our algorithm and a number of previous approaches in hopes of providing a benchmark for future matting research.

Source: Computer Vision and Pattern Recognition, 2007. CVPR '07. IEEE Conference on (2007), pp. 1-8.
EEG-correlated fMRI of human alpha activity.: Neuroimage, Vol. 19, No. 4. (August 2003), pp. 1463-1476.Elec troencephalogr aphy-correlate d functional magnetic resonance imaging (EEG/fMRI) can be used to identify blood oxygen level-dependen t (BOLD) signal changes associated with both physiological and pathological EEG events. Here, we implemented continuous and simultaneous EEG/fMRI to identify BOLD signal changes related to spontaneous power fluctuations in the alpha rhythm (8-12 Hz), the dominant EEG pattern during relaxed wakefulness. Thirty-two channels of EEG were recorded in 10 subjects during eyes-closed rest inside a 1.5-T magnet resonance (MR) scanner using an MR-compatible EEG recording system. Functional scanning by echoplanar imaging covered almost the entire cerebrum every 4 s. Off-line MRI artifact subtraction software was applied to obtain continuous EEG data during fMRI acquisition. The average alpha power over 1-s epochs was derived at several electrode positions using a Fast Fourier Transform. The power time course was then convolved with a canonical hemodynamic response function, down-sampled, and used for statistical parametric mapping of associated signal changes in the image time series. At all electrode positions studied, a strong negative correlation of parietal and frontal cortical activity with alpha power was found. Conversely, only sparse and nonsystematic positive correlation was detected. The relevance of these findings is discussed in view of the current theories on the generation and significance of the alpha rhythm and the related functional neuroimaging findings.

Source: Neuroimage, Vol. 19, No. 4. (August 2003), pp. 1463-1476.
Distinguishing theoretical synaptic potentials computed for different soma-dendritic distributions of synaptic input.: J Neurophysiol, Vol. 30, No. 5. (September 1967), pp. 1138-1168.

Source: J Neurophysiol, Vol. 30, No. 5. (September 1967), pp. 1138-1168.
Study of human occipital alpha rhythm: the alphon hypothesis and alpha suppression: International Journal of Psychophysiolo gy, Vol. 26, No. 1-3. (June 1997), pp. 63-76.Alpha rhythm of the parieto-occipi tal area is comprised of a parade of short-lived cortical excitations (alphons), each of which exhibits oscillations having a stable period within the alpha bandwidth. Strong alpha rhythm is produced by alphons extending over a larger cortical area, although an enhanced cortical current density may also contribute. Local suppression of alpha rhythm indicates when specific cortical areas become engaged in sensory or cognitive functions. Examples are provided for mental imagery, visual memory, auditory memory, and silent rhythming. (c) 1997 Elsevier Science B.V.

Source: International Journal of Psychophysiology, Vol. 26, No. 1-3. (June 1997), pp. 63-76.
Complex haplotypes derived from noncoding polymorphisms of the intronless alpha2A-adrene rgic gene diversify receptor expression: PNAS, Vol. 103, No. 14. (4 April 2006), pp. 5472-5477.alph a 2A-adrenergic receptors (alpha2AAR) regulate multiple central nervous system, cardiovascular , and metabolic processes including neurotransmitt er release, platelet aggregation, blood pressure, insulin secretion, and lipolysis. Complex diseases associated with alpha2AAR dysfunction display familial clustering, phenotypic heterogeneity, and interindividua l variability in response to therapy targeted to alpha2AARs, suggesting common, functional polymorphisms. In a multiethnic discovery cohort we identified 16 single-nucleot ide polymorphisms (SNPs) in the alpha2AAR gene organized into 17 haplotypes of two major phylogenetic clades. In contrast to other adrenergic genes, variability of the alpha2AAR was primarily due to SNPs in the promoter, 5' UTR and 3' UTR, as opposed to the coding block. Marked ethnic variability in the frequency of SNPs and haplotypes was observed: one haplotype represented 70% of Caucasians, whereas Africans and Asians had a wide distribution of less common haplotypes, with the highest haplotype frequencies being 16% and 35%, respectively. Despite the compact nature of this intronless gene, local linkage disequilibrium between a number of SNPs was low and ethnic-depende nt. Whole-gene transfections into BE(2)-C human neuronal cells using vectors containing the entire approx5.3-kb gene without exogenous promoters were used to ascertain the effects of haplotypes on alpha2AAR expression. Substantial differences (P < 0.001) in transcript and cell-surface protein expression, by as much as approx5-fold, was observed between haplotypes, including those with common frequencies. Thus, signaling by this virtually ubiquitous receptor is under major genetic influence, which may be the basis for highly divergent phenotypes in complex diseases such as systemic and pulmonary hypertension, heart failure, diabetes, and obesity. 10.1073/pnas.0 601345103

Source: PNAS, Vol. 103, No. 14. (4 April 2006), pp. 5472-5477.

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