1,721,048 research outputs found
Bilateral Interactions between hands: Associated activity and bilateral deficit
Get PDFMensen hebben een erg goede controle over de bewegingen die hun handen maken en ze zijn ook erg goed in het maken van bewegingen met twee handen tegelijkertijd (bimanuele bewegingen, bijv. pianospelen). Ondanks dat er al veel bekend is over de werking van het motorische systeem, is het nog niet precies bekend welke neurofysiologische mechanismen mensen in staat stelt gecoördineerde bimanuele bewegingen te maken.
Het maken van een gecoördineerde bimanuele beweging vereist uitwisseling van informatie tussen de motor cortices in beide hersenhelften. Deze informatie-uitwisselingen worden ook wel bilaterale interacties genoemd. Ondanks dat voor het verkrijgen van precieze bilaterale interacties tussen de handen veel oefening en training nodig is (bijv. leren je veters te strikken), zijn sommige bilaterale interacties al aanwezig bij de geboorte. De aanwezigheid van deze ingeboren interacties uit zich bijvoorbeeld in de sterke tendens van mensen om hun handen in symmetrie te bewegen (bijv. handen klappen). Wat erg interessant is, is dat de tendens tot symmetrisch bewegen niet alleen zichtbaar is tijdens bimanuele maar ook tijdens unimanuele bewegingen (met 1 hand). Tijdens een sterke of vermoeiende contractie bijvoorbeeld, zal ook de contralaterale hand gaan meebewegen. Deze uiting van ongewilde bimanuele interacties is interessant omdat het ons kan helpen bilaterale interacties tussen de handen te bestuderen. In dit proefschrift onderzoeken we neurofysiologische aspecten van bilaterale interacties tussen de handen, met behulp van ‘ongewilde’ bilaterale interacties zichtbaar tijdens sterke of vermoeiende contracties.
Neuronal mechanisms of motor learning are age dependent
No full textThere is controversy whether age-related neuroanatomical and neurophysiological changes in the central nervous system affect healthy old adults' abilities to acquire and retain motor skills. We examined the effects of age on motor skill acquisition and retention and potential underlying mechanisms by measuring corticospinal and intracortical excitability, using transcranial magnetic stimulation. Healthy young (n = 24, 22 years) and old (n = 22, 71 years) adults practiced a wrist flexion-extention visuomotor task or only watched the templates as an attentional control for 20 minutes. Old compared with young adults performed less well at baseline. Although the absolute magnitude of skill acquisition and retention was similar in the 2 age groups (age x intervention x time, p - 0.425), a comparison of baseline-similar age sub-groups revealed impaired skill acquisition but not retention in old versus young. Furthermore, the neuronal mechanisms differed as revealed by an opposite direction of associations in the age-groups between relative skill acquisition and intracortical facilitation during the task, and opposite changes during skill retention in corticospinal excitability at rest and during the task and intracortical inhibition during the task. (C) 2016 Elsevier Inc. All rights reserved
Perceived fatigue and muscle fatigability in persons with multiple sclerosis
Get PDFPatients with multiple sclerosis (MS) often report increased levels of perceived fatigue, which negatively influence their life. The current thesis studied fatigue in MS patients from different angles. The increased perceived fatigue in MS patients is multifactorial, and a combination of factors is necessary to explain the perceived fatigue. One of these factors is the fatigability of the muscle. The muscle fatigability is caused by both central and peripheral mechanisms. In MS patients the contribution of central factors is larger than in controls, and it seems to be stronger for SPMS patients than RRMS patients. This knowledge may influence future treatments. Muscle fatigability does not only affect physical output, but also a concurrent cognitive task. During a dual task. the greater the muscle fatigability, the stronger the effect on cognitive performance, especially in MS patients. Also, a more complex bimanual task versus a simple bimanual task reduces performance of MS patients more than that of controls. Furthermore, we found that dual tasks are executed differently by young and middle-aged participants. Middle-aged participants prepare less, which results in slower but more accurate responses
Corticospinal excitability during observation and imagery of simple and complex hand tasks: Implications for motor rehabilitation
No full textMovement observation and imagery are increasingly propagandized for motor rehabilitation. Both observation and imagery are thought to improve motor function through repeated activation of mental motor representations. However, it is unknown what stimulation parameters or imagery conditions are optimal for rehabilitation purposes. A better understanding of the mechanisms underlying movement observation and imagery is essential for the optimization of functional outcome using these training conditions. This study systematically assessed the corticospinal excitability during rest, observation, imagery and execution of a simple and a complex finger-tapping sequence in healthy controls using transcranial magnetic stimulation (TMS). Observation was conducted passively (without prior instructions) as well as actively (in order to imitate). Imagery was performed visually and kinesthetically. A larger increase in corticospinal excitability was found during active observation in comparison with passive observation and visual or kinesthetic imagery. No significant difference between kinesthetic and visual imagery was found. Overall, the complex task led to a higher corticospinal excitability in comparison with the simple task. In conclusion, the corticospinal excitability was modulated during both movement observation and imagery. Specifically, active observation of a complex motor task resulted in increased corticospinal excitability. Active observation may be more effective than imagery for motor rehabilitation purposes. In addition, the activation of mental motor representations may be optimized by varying task-complexity. (C) 2010 Elsevier B.V. All rights reserved
Age-related changes in neural plasticity after motor learning
Get PDFIncreasing age is accompanied by structural deteriorations in the brain. Yet, somehow, older adults are still able to learn new motor skills, sometimes even as well as young adults. How do older adults accomplish this? Do they use different (sub)cortical strategies than young adults? It is important to understand the underlying neural mechanisms of motor learning and how these change with increasing age in order to further develop and improve neurorehabilitation programs in patients suffering from impaired motor function. This thesis examined age-related differences in the underlying neural mechanisms of motor learning. The authors used neurostimulation and neuroimaging techniques to examine markers of neural plasticity after both the acquisition and motor memory consolidation of a visuomotor tracking skill in young and older adults. The results show that, while acquiring and retaining the visuomotor skill at similar rates, older compared with young adults use different neural mechanisms when the visuomotor tracking skill is consolidated into motor memory. This might be indicative of alternative neural strategies in older adults to compensate for declines in gray matter volume in the aging brain. The results in this thesis provides new knowledge that is important for tailoring neurostimulation programs to the patient’s age and the stage of motor learning
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
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
Inter-limb mechanisms and clinical relevance of cross-education in humans
Get PDFAl meer dan 100 jaar is bekend dat krachttraining met één arm of been zowel het getrainde als niet-getrainde ledemaat sterker maakt. Dit fenomeen wordt cross-education genoemd. De krachttoename van het niet-getrainde ledemaat bedraagt gemiddeld 52% van het getrainde ledemaat en kan worden verklaard door middel van twee theorieën. Het geheugenspoor van de getrainde beweging is of toegankelijk voor beide hersenhelften of bevindt zich in beide hersenhelften. De literatuurstudie laat zien dat het spiegelneuronen systeem, dat visuele informatie van de beweging via sensorische neuronen verbindt met de motoneuronen die de beweging uitvoeren, ook een rol speelt in cross-education. Observatie van eenzijdige bewegingen in een spiegel zou daarom de transfer naar de niet-getrainde zijde moeten vergroten ten opzichte van training zonder een spiegel. Als verondersteld, spiegeltraining leidt acuut tot een afname in intracorticale prikkelbaarheid van de primaire motorische cortex en chronisch tot een toename van het cross-education effect en een afname in intracorticale inhibitie. Onderzoek naar de klinische relevantie van deze neurofysiologische bevindingen laat zien dat patiënten na een voorste kruisband (VKB) ruptuur neuromusculaire gebreken vertonen in zowel het geblesseerde als niet-geblesseerde been. Een randomized clinical trial werd uitgevoerd om te zien of quadriceps zwakte in het geopereerde been na een VKB reconstructie kan worden verminderd door extra krachttraining te doen met het niet-geblesseerde been. De cross-education training leidde niet tot sneller herstel na de VKB operatie ten opzichte van de reguliere revalidatie. Cross-education zou wel zinvol kunnen zijn voor patiënten die de aangedane zijde niet kunnen trainen vanwege immobilisatie
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