1,720,961 research outputs found
Oszillatorische Gamma-Band-Aktivität bei der Verarbeitung auditorischer Reize im Kurzzeitgedächtnis im MEG
No full textRecent studies have suggested an important role of cortical gamma oscillatory activity (30-100 Hz) as a correlate of encoding, maintaining and retrieving auditory, visual or tactile information in and from memory. It was shown that these cortical stimulus representations were modulated by attention processes. Gamma-band activity (GBA) occurred as an induced response peaking at approximately 200-300 ms after stimulus presentation. Induced cortical responses appear as non-phase-locked activity and are assumed to reflect active cortical processing rather than passive perception. Induced GBA peaking 200-300 ms after stimulus presentation has been assumed to reflect differences between experimental conditions containing various stimuli. By contrast, the relationship between specific oscillatory signals and the representation of individual stimuli has remained unclear. The present study aimed at the identification of such stimulus-specific gamma-band components. We used magnetoencephalography (MEG) to assess gamma activity during an auditory spatial delayed matching-to-sample task. 28 healthy adults were assigned to one of two groups R and L who were presented with only right- or left-lateralized sounds, respectively. Two sample stimuli S1 with lateralization angles of either 15° or 45° deviation from the midsagittal plane were used in each group. Participants had to memorize the lateralization angle of S1 and compare it to a second lateralized sound S2 presented after an 800-ms delay phase. S2 either had the same or a different lateralization angle as S1. After the presentation of S2, subjects had to indicate whether S1 and S2 matched or not. Statistical probability mapping was applied to the signals at sensor level to identify spectral amplitude differences between 15° and 45° stimuli. We found distinct gamma-band components reflecting each sample stimulus with center frequencies ranging between 59 and 72 Hz in different sensors over parieto-occipital cortex contralateral to the side of stimulation. These oscillations showed maximal spectral amplitudes during the middle 200-300 ms of the delay phase and decreased again towards its end. Additionally, we investigated correlations between the activation strength of the gamma-band components and memory task performance. The magnitude of differentiation between oscillatory components representing 'preferred' and 'nonpreferred' stimuli during the final 100 ms of the delay phase correlated positively with task performance. These findings suggest that the observed gamma-band components reflect the activity of neuronal networks tuned to specific auditory spatial stimulus features. The activation of these networks seems to contribute to the maintenance of task-relevant information in short-term memory.Ergebnisse aus aktuellen Studien legen nahe, dass kortikale oszillatorische Aktivität im Gamma-Bereich (30-100 Hz) eine wichtige Rolle für verschiedene kognitive Prozesse spielt. Dazu zählen das Kodieren, die Aufrechterhaltung und der Abruf auditorischer, visueller oder taktiler Informationen in das bzw. aus dem Gedächtnis. Es konnte gezeigt werden, dass diese kortikale Aktivität durch Aufmerksamkeitsprozesse beeinflusst wird. Gamma-Aktivität trat bei vorangegangenen Untersuchungen als induzierte Antwort ca. 200-300 ms nach Stimuluspräsentation auf. Es wird angenommen, dass diese nicht phasengebundenen kortikalen Reizantworten aktive kortikale Verarbeitungs-prozesse widerspiegeln. In früheren Studien wurde induzierte Gamma-Aktivität während der Aufrechterhaltung von Stimulusinformationen über Regionen gefunden, die an der Verarbeitung aufgabenrelevanter Reizmerkmale beteiligt sind. Diese Antworten im Gamma-Bereich spiegelten Unterschiede zwischen verschieden experimentellen Bedingungen wider, jedoch ist wenig über die Repräsentation spezifischer Stimuluseigenschaften durch Gamma-Aktivität bekannt. Mit der vorliegenden Studie haben wir versucht, solche stimulus spezifischen Gamma-Komponenten zu untersuchen. Dafür verwendeten wir Magnetenzephalographie (MEG) und eine auditorische räumliche “delayed matching-to-sample“ Aufgabe. 28 gesunde Erwachsene wurden dabei zwei verschiedenen Gruppen zugeordnet. Gruppe R bekam rechtslateralisierte Stimuli präsentiert, während diese in Gruppe L linkslateralisiert waren. Dabei unterschieden sich die Reize nur in ihrer räumlichen Charakteristik, die Klangmuster blieben unverändert. In beiden Gruppen wurden zwei Beispielstimuli S1 mit Lateralisierungswinkeln von 15° bzw. 45° verwendet. Die Probanden mussten sich den Lateralisierungswinkel von S1 merken und anschließend mit einem zweiten Stimulus S2, der nach einer Verzögerungsphase von 800 ms präsentiert wurde, vergleichen. S2 hatte dabei entweder den gleichen Lateralisierungswinkel wie S1, oder unterschied sich darin von dem ersten Stimulus. Nach der Präsentation von S2 mussten die Probanden signalisieren, ob die Lateralisierungswinkel der beiden Stimuli übereinstimmten oder nicht. Die Signale der einzelnen Sensoren wurden mit einem statistischen Wahrscheinlichkeitsmapping untersucht. Dabei wollten wir Unterschiede in der spektralen Amplitude für Stimuli mit 15° bzw. 45° Lateralisierungswinkel identifizieren. Wir konnten spezifische Gamma-Aktivität für alle Beispielstimuli nachweisen. Die Signale wurden im Bereich von 59-72 Hz gefunden und waren über dem parieto-okzipitalen Kortex jeweils kontralateral zur stimulierten Seite lokalisiert. Die maximalen Spektralamplituden dieser Oszillationen traten während der mittleren 200-300 ms der Verzögerungsphase auf und nahmen zu ihrem Ende hin ab. Zusätzlich haben wir Korrelationen zwischen der Aktivierungsstärke der Gamma-Komponenten und dem Abschneiden bei der Gedächtnisaufgabe untersucht. Dabei zeigte sich, dass der Unterschied der oszillatorischen Antworten auf bevorzugte und nicht-bevorzugte Stimuli während der letzten 100 ms der Verzögerungsphase positiv mit der Leistung in der Gedächtnisaufgabe korrelierte. Diese Ergebnisse sprechen dafür, dass die beobachteten Gamma Komponenten die Aktivität neuronaler Netzwerke, die auf die Verarbeitung räumlicher auditorischer Information spezialisiert sind, widerspiegeln. Die Aktivierung dieser Netzwerke scheint zur Aufrechterhaltung aufgabenbezogener Information im Kurzzeitgedächtnis beizutragen
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Cortical excitability and interhemispheric connectivity in early relapsing–remitting multiple sclerosis studied with TMS-EEG
Get PDFEvoked potentials (EPs) are well established in clinical practice for diagnosis and prognosis in multiple sclerosis (MS). However, their value is limited to the assessment of their respective functional systems. Here, we used transcranial magnetic stimulation (TMS) coupled with electroencephalography (TMS-EEG) to investigate cortical excitability and spatiotemporal dynamics of TMS-evoked neural activity in MS patients. Thirteen patients with early relapsing–remitting MS (RRMS) with a median Expanded Disability Status Scale (EDSS) of 1.0 (range 0–2.5) and 16 age- and gender-matched healthy controls received single-pulse TMS of left and right primary motor cortex (L-M1 and R-M1), respectively. Resting motor threshold for L-M1 and R-M1 was increased in MS patients. Latencies and amplitudes of N45, P70, N100, P180, and N280 TMS-evoked EEG potentials (TEPs) were not different between groups, except a significantly increased amplitude of the N280 TEP in the MS group, both for L-M1 and R-M1 stimulation. Interhemispheric signal propagation (ISP), estimated from the area under the curve of TEPs in the non-stimulated vs. stimulated M1, also did not differ between groups. In summary, findings show that ISP and TEPs were preserved in early-stage RRMS, except for an exaggerated N280 amplitude. Our findings indicate that TMS-EEG is feasible in testing excitability and connectivity in cortical neural networks in MS patients, complementary to conventional EPs. However, relevance and pathophysiological correlates of the enhanced N280 will need further study
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
