1,720,983 research outputs found
High temporal resolution microdialysis reveals cholinergic spikes preceding upshifts in attentional performance.
No full textPrefrontal cholinergic neurotransmission mediates the cognitive control of attention and the detection of cues. Two modes of cholinergic neurotransmission can be separated. Relatively slow or tonic (tens of seconds or minutes) modulate cortical circuitry as a function of the demands on attention (St. Peters et al, 2011). Fast, second-based release events (or transients) are generated via local cortical circuitry and are necessary for the detection of cues (Hasselmo & Sarter 2011). Transients are recorded using amperometry and enzyme-coated microelectrodes. Tonic levels of cholinergic neurotransmission are monitored by microdialysis; importantly this is not a confound of the necessity of long collection intervals but our evidence indicates that tonic levels are not merely representing integrated transients. To further test this hypothesis and to explore the timescale of variations in tonic cholinergic activity in a given behavioral context and to refine the relationships between behavioral/cognitive processes and such variations, we employed a novel HPLC-tandem mass spectrometry (MS) method (Song et al, 2012) to detect acetylcholine (ACh) and several monoamines and amino acids from 3-min collections (1 μL/min; no AChesterase inhibitor added). The focus on 3-min collections was based on our observation that rats performing the sustained attention task (SAT) frequently shift between good and poor levels of performance (defined as SAT scores >0.34 and at chance, or <0.17, respectively). Averaged across SAT sessions, ACh release levels corresponded with those previously obtained from 8-min collections and conventional HPLC-EC methods. However, performance-associated ACh levels fluctuated drastically across 3-min collections, ranging from pre-task baseline levels to 500% above baseline. Cholinergic spikes were observed just prior to shifts from random levels of performance to good levels of performance. Specifically, over 14 animals, 75% of such up-shifts were preceded by increases in cholinergic neurotransmission that were at least 3 SD above baseline levels. These findings indicate the usefulness of high temporal resolution microdialysis. The results are consistent with the hypothesis that tonic cholinergic activity modulates cortical target circuitry as a function of the subjects’ motivation to enhance attentional performance and to orchestrate, the mechanisms designed to enhance signal processing, noise filtering and task compliance (Sarter & Paolone 2011). Tonic cholinergic activity in SAT performing animals is a major target of treatments designed to benefit cognitive performance in ADHD, schizophrenia, PD and other disorders
Sampling from injured tissue as a blessing in disguise: tonic changes in cholinergic neurotransmission using microdialysis
No full textPrefrontal cholinergic transmission in damaged and intact tissue from naive and treated rats via in-vivo microdialysi
Sampling from injured tissue as a blessing in disguise: tonic changes in cholinergic neurotransmission using microdialysis.
No full textWith the advent of enzyme-coated microelectrodes and the amperometric method for assessing synaptic acetylcholine (ACh) release [1], and following the demonstration of behavioral performance-associated cholinergic transients [2], microdialysis no longer appeared to be a useful or even justifiable method for measuring extracellular ACh concentrations. Numerous major limitations have been cited to plague this method, ranging from the implications of tissue injury resulting from the implantation of relatively large probes to the poor spatial definition of the area that contributes to recovered ACh. Moreover, microdialysis-based claims for (tonic) changes in ACh levels on the scale of minutes have been considered mere artifacts of the limits of detection of conventional analytical methods. The hypothesis that all cholinergic neurotransmission is phasic (scale of [milli-] seconds) contrasts with the hypothesis that low micromolar “ambient levels” of extracellular ACh are regulated by levels of acetylcholinesterase (AChE) [3]. Because our experiments using choline oxidase (CO)-coated microelectrodes as well as electrodes with co-coatings of AChE plus CO did not indicate the presence of non-hydrolized ACh even after (massive) neuronal depolarization [4], the presence - or at least the concentration - of such “ambient levels” of extracellular ACh has remain unsettled. Below we summarize evidence indicating that by using microdialysis we can observe systematic relationships between minutes-based extracellular ACh levels and behavioral/cognitive manipulations and performance, and that it is unlikely that these minute-based changes merely represent integrated cholinergic transients. We speculate that the pathological consequences of microdialysis probe insertion produces a sphere with reduced or absent AChE concentrations, allowing a tonic component of cholinergic neurotransmission to be detected by this method. Although the physiological significance of such measures remains unclear, their psychobiological relevance suggests that the aspects of the microdialysis method that were previously considered detrimental may in fact conspire to allow the measurement of meaningful, slow changes in cholinergic activity. Method
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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