118,973 research outputs found
Gamma flicker triggers attentional selection without awareness
No full textGamma band modulations in neural activity have been proposed to mediate attentional processes. To support a causal link between gamma activity and attentional selection, we attempt to evoke gamma oscillations by a 50-Hz subliminal flicker. We find that a subliminal 50-Hz flicker at a target location, before target presentation, speeds up and enhances target detection and discrimination. This effect is specific to the middle of the gamma range because it is not evident at <35-Hz flicker. It requires 300 ms to build up, dissipates within 250 ms of flicker offset, and shows a tendency to invert after 500 ms. The results are discussed in relation to a role for gamma band neural synchrony in the allocation of visual attention
Efficacy of nicergoline in dementia and other age associated forms of cognitive impairment.
No full textBACKGROUND: Nicergoline is an ergot derivative currently in use in over fifty countries for more than three decades, for the treatment of cognitive, affective, and behavioral disorders of older people. It was initially considered as a vasoactive drug and mainly prescribed for cerebrovascular disorders. Recent findings suggest other actions which has provided a rationale for the use of nicergoline for the treatment of various forms of dementia, including Alzheimer's Disease. OBJECTIVES: To determine whether there is evidence of efficacy of nicergoline in the treatment of dementia and other age-associated forms of cognitive decline,and to assess the safety and tolerability of the drug. SEARCH STRATEGY: 1. Electronic databases search. The Cochrane Controlled Trials Register (which contains citations from the MEDLINE, EMBASE, Psych LIT, and hand searches of geriatric, dementia, psychogeriatric journals, and conference abstracts) was searched using the following terms: 'Nicergoline', 'Sermion'. 2. Reference search. The reference lists of all obtained studies was checked. 3. Pharmaceutical company Pharmacia & Upjohn, owners of the rights to produce and market nicergoline in various different countries, was asked to provide data and reports of clinical trials. In case of unavailability of numerical data in published studies, the authors of each paper, were asked for any published or unpublished data. SELECTION CRITERIA: - All unconfounded, double-blind, randomized, placebo-controlled, published and unpublished trials were sought. Non-randomized trials were excluded. Open trials were considered for inclusion if patients were randomized to the different treatment groups. - All patients diagnosed as having dementia or other cognitive disorder defined according to classification criteria accepted at the time of each study. - Nicergoline given at any dose for more than one day with placebo control. Type of outcome variables: 1. Cognitive function (as measured by psychometric tests). 2. Clinical impression (such as CIBIC or other clinical global measures of change). 3. Functional performance including dependency. 4. Behavioural disturbance. 5. Safety and acceptability as measured by the incidence of adverse effects (including side-effects) leading to withdrawal. 6. Death 7. Effect on carer 8. Use of services 9. Quality of life. DATA COLLECTION AND ANALYSIS: A comprehensive search of the international literature and the producing company archives has been performed to identify all possible sources of data for this review. Only those trials fulfilling the inclusion criteria of belonging to either category A or B of allocation concealment, as defined by the Cochrane Organisation, were examined for data extraction by one reviewer. If there was doubt then the other reviewer was consulted. Data availability restricted analyses to 'completers' analyses for the outcome measures. Outcomes able to be assessed included: Behaviour, Cognition, Clinical Judgment, Tolerability, EEG. MAIN RESULTS: The Sandoz Clinical Assessment Geriatric Scale (SCAG) was the outcome used in the largest number of patients (814 patients). The results from these studies were homogeneous in nature despite including patients observed for periods of time ranging from 2 months to 12 months. There was a difference in favour of the active treatment in reducing the behavioural symptoms described by this scale, -5.18 points [-8.03, -2.33]. This scale has a maximum of 133 points. The therapeutic effects of nicergoline seem to be evident by 2 months of treatment and maintained for 6 months. In general other behavioural outcome measures which include the GRS, the IADL, and the MACC and were episodically used in few studies, failed to demonstrate statistically significant results although there was a trend favouring treatment. Cognitive assessment has been performed in a moderate number of patients with the MMSE (261 patients) and the ADAS-Cog (342 patients). No significant heterogeneity was found for these trials, despite the trials extending over periods of treatment of 3 to 12 months. There was a difference between treatment and control groups on the MMSE favouring nicergoline treatment. At 12 months the effect size was 2.86 [0.98, 4.74] The effect size for the ADAS-Cog, used exclusively with Alzheimer's disease patients, did not reveal a significant benefit. At 12 months the trend favoured treatment (-1.64 [-4.62, 1.34]). The other results from various cognitive measures tended to favour nicergoline but this was based on a small number of cases. The clinical impression of change obtained from a total of 921 patients was homogeneous across the studies, despite reflecting changes over periods of time ranging from 2 to 12 months. The Peto odd ratio for improvement in the subjects treated with nicergoline over these varying time periods was 3.33 [2.50, 4.43]. Tolerability assessed in 1427 patients was homogeneous across all studies and demonstrated a mildly increased risk of adverse events on treatment, OR 1.51[1.10, 2.07]. REVIEWER'S CONCLUSIONS: The clinical studies on nicergoline were carried out with diverse criteria and modalities of evaluation. Despite this, the 14 studies included in this review, have presented generally consistent results. Results of this meta-analysis provide some evidence of positive effects of nicergoline on cognition and behaviour and these effects are supported by an effect on clinical global impression. There was some evidence that there were increased risk of adverse effects associated with nicergoline. These results were obtained on older patients with mild to moderate cognitive and behavioural impairment of various clinical origins, including chronic cerebrovascular disorders and Alzheimer's dementia. The few studies specifically performed on patients with Alzheimer's disease were performed with too few people to give a definitive answer to the questions concerning the use of nicergoline for this form of dementia. This drug has not been evaluated using current diagnostic categories such as MCI or in association with therapeutic agents of different nature such as cholinesterase or antioxidant drugs
Effects of “Short-Term” versus “Long-Term” L-Dopa Therapy in Parkinsonism on Critical Flicker Frequency
No full text This study investigated shorter and longer range effects of L-Dopa therapy in parkinsonism on critical flicker frequency (CFF) scores. Three equated groups of 15 Ss were selected to include “short-term,” “long-term,” L-Dopa patients and a control group. Binocular CFF thresholds were obtained for each S on two separate occasions. Results indicate that: (1) the control group scored significantly higher on CFF indicating superior neural integration when compared with the “short-term” or “long-term” L-Dopa group; (2) the “short-term” L-Dopa group scored significantly higher than the “long-term” L-Dopa group demonstrating better cerebral efficiency. Evidence suggests that a peculiar clinical state interfering with neural transmission may develop in parkinsonian patients on L-Dopa therapy prolonged 2 yr. or more. </jats:p
Voltage flicker estimation based on linearization and L-p norms
No full textThis paper presents an approach to estimate voltage flicker components magnitudes and frequencies. The approach is based on L-p norms (p = 1, 2 and infinity) and Taylor series linearization. Effects of sampling frequency, number of samples, time interval, and noise are introduced. The main result is that it is possible to design an L-p estimator to identify flicker frequency and amplitude from time series measurements
Lp norm approaches for estimating voltage flicker
No full textIt is important to accurately estimate instantaneous voltage flicker magnitudes and frequencies in order to correctly evaluate voltage fluctuations. Voltage flicker is a problem in electric power quality. Different approaches used to determine the magnitude of the voltage flicker have been presented: measurement methods generally use a flickermeter device. Simulation methods require a computer model of the disturbing load and the flickermeter. Calculation methods necessitate a simplified empirical formula. Estimation algorithms are based on the estimation of the voltage flicker components. In this paper, two models of voltage flicker are discussed: L-p estimation algorithms utilizing L-1.L-2 and L-infinity norms are used to estimate the voltage magnitudes of the flicker signals as well as the fundamental voltage magnitude. The main result is that it is possible to design an L-p estimator to identify flicker frequency and amplitude from time series measurements. (C) 2010 Elsevier B.V. All rights reserved
Assessment of human annoyance under flicker condition
No full textThe international standard EN 61000-4-15 gives functional and design specifications for the Flickermeter currently used to evaluate the flicker severity, as defined in the International Electrotechnical Vocabulary. That instrument doesn't work properly if light sources different than incandescent-filament one are considered. This paper is aimed at presenting a step towards an innovative Flickermeter which is able to account a larger variety of luminous sources. In particular, the goal of this study is to find a new method to define the human annoyance under flicker condition, based on the measurement of the pupil size in presence of different flicker stimuli. The design and characterization of an automatic system able to generate flicker and measure the pupil size will be presented. In addition, the results obtained on human subject will be illustrated
On a Relation between the Flicker value and the Working Condition
No full textThe appropriate disposition of the worker improves the ability of the worker and the efficiency of the labor and further decreases the rate of inferior goods and the rate of accidents. In previous paper, the variation of the flicker value, the trend of the miss frequency and the relation between them under the condition which has one surveillance point and one back-ground condition are analyzed. In this paper, the surveillance point is increased to two points and the back ground condition also two in order to examine which condition influences strongly to the flicker value in the working time. It was found that the variation of the flicker value is strongly connected with the qualification, the number of the surveillance and its miss-frequency
Experimental Evaluation of Flicker Effects on Human Subjects
No full textFlicker annoyance measurement, no matter if it is performed by processing the supplying voltage or by evaluating the light emitted by the lamp, relies on the assumption of a proper model of the behavior of the complex eye-brain system in presence of fluctuating light. The only experimental data available are the ones obtained, for a certain incandescent lamp, by asking several people to report their perception about flicker they were subjected to. In this paper, the possibility of achieving an "objective" evaluation of the flicker effects on human subject is investigated. In particular, the increment of the blood flow in a vessel at the optic nerve papilla is considered and taken as possible index of the annoyance due to flicker
A simple Lamp-Eye-Brain Model for Flicker Observations
No full textThis paper suggests a simple eye-brain model for light flicker studies and examines the response of such a model to voltage flicker. Calculated flicker curves representing the objectionable threshold of voltage fluctuation were found to match reasonably well the experimental IEEE curves. The model may be used to predict flicker curves for diverse voltage flicker waveforms and for lamps with different time constants and gain factors
Impaired endothelial function of the retinal vasculature in hypertensive patients
No full text<p><b>Background and Purpose:</b> Arterial hypertension constitutes a central factor in the pathogenesis of stroke. We examined endothelial function of the retinal vasculature as a model of the cerebral circulation.</p>
<p><b>Methods:</b> Thirty-eight young subjects (19 hypertensive and 19 normotensive) were treated with the AT1-receptor blocker candesartan cilexetil and placebo, each over 7 days. Retinal capillary flow and blood flow velocity in the central retinal artery were assessed with scanning laser Doppler flowmetry and pulsed Doppler ultrasound, respectively. NG-monomethyl-L-arginine (L-NMMA) was infused to inhibit nitric oxide (NO) synthesis. Diffuse luminance flicker was applied to stimulate NO release.</p>
<p><b>Results:</b> In normotensive subjects, L-NMMA decreased retinal capillary flow by 8.2%±13% (P<0.05) and flickering light increased mean blood flow velocity in the central retinal artery by 19%±29% (P<0.01). In contrast, no significant change to these provocative tests was seen in hypertensive subjects. Treatment with candesartan cilexetil restored a normal pattern of reactivity in retinal capillaries (L-NMMA: decrease in perfusion by 10%±17%, P<0.05) and the central retinal artery (flicker: increase in mean blood flow velocity by 42%±31%, P<0.001) in hypertensive patients.</p>
<p><b>Conclusions:</b> Endothelial function of the retinal vasculature is impaired in early essential hypertension but can be improved by AT1-receptor blockade.</p>
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