1,721,004 research outputs found
Hemispheric asymmetries in goal-directed hand movements are independent of hand preference
No full textAsymmetries in the kinematics and neural substrates of voluntary right and left eye-hand coordinated movements have been accredited to differential hemispheric specialization. An alternative explanation for between-hand movement differences could result from hand-preference related effects. To test both assumptions, an experiment was conducted with left- and right-handers performing goal-directed movements with either hand paced by a metronome. Spatiotemporal accuracy was comparable between hands, whereas hand peak velocity was reached earlier when moving with the left compared to the right hand. The underlying brain activation patterns showed that both left- and right-handers activated more areas involved in visuomotor attention and saccadic control when using their left compared to the right hand. Altogether, these results confirm a unique perceptuomotor processing specialization of the left brain/right hand system that is independent of hand preference.sponsorship: Werner Helsen and Ann Lavrysen acknowledge the KU Leuven Research Council for their support of this research project (OT/00/40). The authors also wish to thank Ir. Marc Beirinckx and Ir. Paul Meugens for providing invaluable guidance in designing the research equipment and the electronics. (KU Leuven Research Council|OT/00/40)status: Publishe
Het verbeteren van neuroplasticiteit en motorisch leren door middel van hersenstimulatietechnieken
No full textNeuroplasticity refers to the ability of the brain to change as a result of one's experience, indicating that the brain is plastic and malleable. Synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases of activity. In the clinical context it determines how patients with a brain injury can recover, e. g. after stroke, in order to regain independence and to perform daily life activities (e.g. dressing, eating, self-care and personal hygiene). Previous studies have demonstrated that plasticity can be enhanced by different mechanisms.
In this PhD project we tested the effectiveness of non-invasive brain stimulation techniques to influence neuro-plasticity.
First, we tested reward related interventions which previously have been proved to boost neuroplasticity. For example monetary reward has been shown to improve the acquisition and particularly long-term retention of a newly acquired motor skill in humans. The physiological substrate mediating this effect is most likely dopamine (DA), a neuromodulator influencing cognitive, emotional, motivational and motor processes.
Secondly, we tested the effect of transcranial Direct Current Stimulation (tDCS), known to promote neuroplasticity, in healthy young volunteers. Previous research suggests that anodal tDCS over the primary motor cortex (M1) modulates NMDA receptor dependent processes that mediate synaptic plasticity. We tested this proposal by applying anodal versus sham tDCS while the subjects practiced to flex their thumb as fast as possible. The repetitive practice of this task has been shown to result in performance improvements that reflect use-dependent plasticity resulting from NMDA receptor mediated, long-term potentiation (LTP)-like processes. While, tDCS has received much attention because it can be easily applied in a clinical context, its underlying mechanisms are not clear yet. In order to explore its mechanisms of action we decided to develop an animal model.
In the third experiment, we developed an animal model of stroke rehabilitation that better mimics tDCS applications in humans. Here we aimed to develop an animal model where the effect of anodal tDCS over ipsilesional M1 is tested while animals perform goal-directed limb training. Accordingly, rats were trained on the pasta matrix reaching task, which allows the manipulation of limb use in order to mimic human clinical phenomena. We induced photothrombotic stroke in the M1 contralateral to the preferred limb. The photothrombotic stroke animal model aims to induce ischemic damage within a cortical area through photo-activation of a light-sensitive dye previously injected in the blood system.
We concluded that behavioural markers of use-dependent plasticity are surprisingly insensitive to monetary reward or punishment which might result from the nature of the task. Our data suggest that anodal tDCS facilitates long-term memory formation reflecting use-dependent plasticity, supporting the idea that anodal tDCS facilitates synaptic plasticity mediated by an LTP-like mechanism. Our data also showed that the application of anodal tDCS during post-stroke training on a reaching and grasping task in rats is feasible. tDCS is beneficial to upper limb recovery, only when the animals performed the grasp training. The availability of an animal model that can be used to closely mimic recovery training in stroke patients opens new avenues for gaining more mechanistic understanding of the underlying principles. Our results suggest that tDCS is a promising adjuvant therapy to facilitate motor recovery following stroke.status: Publishe
Het vormen van motorisch geheugen: een neurale en gedragsmatige studie
No full textMemory formation covers unique and divergent stages. After performing a new action, encoding takes place and forms a representation of this action in the brain. The novel memory trace is then stabilized through subsequent stages of a time dependent process referred to as memory consolidation. Consolidation makes the memory more resistant against competing influences, interference or forgetting in the absence of further practice and allows retention and retrieval in the future. However, upon recall the memory becomes modifiable again since reactivation of a stable memory destabilizes the memory representation. In order to persist over longer time-periods, these reactivated memories require re-stabilization; i.e. a process called reconsolidation. The aim of this doctoral project was to investigate the dynamics of motor memory formation with a specific focus on the three fundamental underlying processes: encoding, consolidation, and recall.
In the first part of this doctoral project, we investigated the role of sleep in maintaining the capacity for motor memory encoding. The study rationale was based on the synaptic homeostasis hypothesis which suggests that the evident homeostatic regulation of sleep and sleep need is linked to mechanisms of plasticity and learning capabilities of the brain. We reported, in line with the synaptic homeostasis hypothesis, that baseline corticomotor excitability increased after a 12h-period awake and that the brain’s capacity to exhibit motor learning-induced plasticity was reduced by the end of the day. We show that especially slow wave sleep is necessary to renormalize the daily increase in synaptic strength due to spontaneous synaptic plasticity when awake and restore the brain’s capacity to encode new memories. In the second part, we focused on the role of movement observation in motor memory consolidation. We reported that observing the same type of movement as previously practiced (congruent movement stimuli) substantially improved performance on a retention test shortly after training in comparison to observing either an incongruent movement type or control stimuli. On the other hand, no differences in retention were found when either observation followed 24h after initial training. In summary, we showed that once a motor memory is encoded, movement observation is a practical tool to improve early consolidation. In the third part, we investigated the role of reconsolidation upon motor memory recall. We observed that the memory is only fragile for interference during a short time window and further physical practice or even the simple passage of time will re-stabilize the reactivated motor memory. This shows that both length of reactivation and timing of interference constrain whether a memory can be experimentally interfered with and suggests that the role of reconsolidation is to maintain memory relevance for future use.
In summary, this doctoral project reflects the complexity of human motor memory formation, and contributes to further the understanding of these fundamental processes for human memory.status: Publishe
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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