1,720,976 research outputs found
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
Hypothalamic dopamine neurons project to brainstem regions related to movement
No full textLocomotion is a complex behaviour resulting from interactions between the brain and spinal cord. Dopamine modulates locomotion via ascending projections to the basal ganglia and descending projections to the mesencephalic locomotor region (MLR). The MLR is a region in the brainstem known to initiate and control locomotion. Motor commands from supraspinal structures are relayed to the spinal cord via the medullary reticular formation (MRF). However, it remains uncertain if dopamine neurons also innervate regions of the MRF known to influence locomotor activity. Using a retrograde viral tracing approach, I identified a discrete dopaminergic pathway that extends from the A11 region of the posterior hypothalamus to locomotor regions of the MRF. Furthermore, using an anterograde viral tracing technique, I found that dopamine neurons of the A11 region project throughout the rostrocaudal extent of the MRF and terminate predominantly ipsilaterally. Contrastingly, using immunohistochemistry, I show that neurons in the MRF are devoid of D1 receptors. Lastly, using the genetically encoded dopamine sensor dLight1.2 and fibre photometry, I provide evidence of altered dopamine transients during locomotor activity. Together, these results suggest that dopaminergic innervation of the MRF is sparse and originates primarily from the A11 region of the posterior hypothalamus. Further investigation is required to determine the functional contributions to neural circuits in the MRF
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
Rapid feedback responses when planning, performing and terminating goal-directed reaching movements
No full textThe healthy nervous system transitions seamlessly between actions with different goals. A tennis player, for example, waits in a ready position before lunging sideways to return a serve. This simple action involves disengaging from posture to perform the movement and then stabilizing again after contact to prepare for the next return. These transitions occur seamlessly despite evidence that the neural control supporting these goals may be distinct. We know little about how neural control changes when transitioning between these distinct goals. Here, we examined how healthy participants corrected their movements when disturbed by mechanical perturbations (n = 40; 20 females) while planning, performing, and terminating a movement (Experiment 1). Hand displacement and muscle activity were measured to quantify feedback responses and assess changes in neural control. We found that participants were displaced less and generated larger muscle responses when disturbed during movement compared to when holding posture prior to movement or after reengaging posture control in the goal target. Additionally, peak displacements were smaller, and muscle responses were larger when reengaging posture control in the goal target compared to holding posture during the planning phase before movement. The contribution of each muscle varied across the phases of movement and was shaped by the level of activity when the disturbance occurred. Pre-existing muscle activity impacted the responsiveness of individual muscles. Therefore, we added a background load to observe how it altered the amplitude and scaling of corrective responses. Participants countered a background load that excited the elbow extensor muscles (Experiment 2). They also encountered the same perturbations as Experiment 1. When the background load was applied, it reduced peak displacements and increased the amplitude of muscle responses, particularly when the loaded muscle was stretched by the perturbation. Indeed, the background load increased sensitivity to proprioceptive information, especially when the loaded muscle was stretched by the perturbation. Overall, our findings demonstrate that the nervous system alters its neural control when engaging in movement from posture (and vice versa). The nervous system is more sensitive to sensory feedback when moving and the least sensitive to the same perturbations when maintaining posture before movement
Electrical Vestibular Stimulation for Probing the Effect of Combat Sports on Balance Control
No full textCombat athletes are at a high risk for head injuries such as concussion. Recent work has uncovered that even repetitive head impacts (RHIs) may have lasting effects on cognitive, emotional, and motor function. This thesis will focus on the changes to vestibulospinal processing seen in combat athletes. Electrical vestibular stimulation (EVS) was used to evoke vestibulospinal reflexes, comparing the resulting responses between combat athletes and healthy sex/age matched controls. This is described through three separate chapters. First, I test the differences in electromyography (EMG) responses, then develop a novel EVS-induced postural sway thresholding technique, and finally investigate the EVS threshold differences between the fighters and controls. The experimental results of the first study demonstrated frequency-specific changes in vestibular sensitivity to EVS for combat athletes, via EMG responses. Combat athletes showed an increased sensitivity to low frequency EVS, and a decreased sensitivity to high frequency EVS, resulting in increased latencies on short and medium latency reflexes, scaling with increasing career RHI exposure. The second study presented shows that stochastic electric vestibular stimulation (SVS) can be used to determine EVS postural sway thresholds much lower than those that have previously been shown in the literature. The second study also shows that humans appear to be more sensitive to bipolar EVS than monopolar EVS. The third study found that combat athletes had lower EVS-induced sway thresholds using low frequency EVS than their matched controls. Taken together this thesis displays significant changes to vestibulospinal processing with increased RHI exposure in combat athletes
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
Learning to Balance an Inverted Pendulum at the Fingertip: A Window Into the Task and Context-Dependent Control of Unstable Dynamical Objects
Full text linkOur ability to control unstable objects highlights the sophistication of voluntary motor behaviour. In this thesis, we used an inverted pendulum (i.e., stick) balancing paradigm to investigate the task, learning and context-dependent attributes of unstable object control. We hypothesized that learning would mediate the functional integration of posture and upper limb dynamics and expected changes in the task demand and context to be reflected in the control of posture and the upper limb. We found that training increased the average length of balancing trials and applied this result to further investigate the circumstantial properties of unstable object control. We investigated the temporal structure of posture and upper limb dynamics using statistical and nonlinear time series analysis. We demonstrated that subjects used an intermittent strategy to control the inverted pendulum (Chapters 3 and 5) and found that motor learning modulated the statistical and spatiotemporal attributes of posture (Chapter 5) and upper limb displacements (Chapters 2, 3 and 5). We confirmed the balance control strategy was intermittent by showing that posture and upper limb time series are composed of two independent timescale components: a fast component linked to small stochastic displacements and a slow component related to feedback control (Chapters 3, 4 and 5). The interplay between timescale components was affected by the balancing context (Chapter 3) and task demand (Chapter 4). Chapter 5 investigated the acquisition of individual and coupled posture-upper limb control mechanisms. We found that motor learning involved two independent adaptation processes. The first process modified the timescale composition of posture and upper limb displacements and was followed by incremental changes in the occurrence and duration of correlated posture-upper limb trajectories. In Chapter 6, we investigated learning-mediated changes in multijoint coordination and control. Motor learning led to the flexible, error-compensating recruitment of individual joints and we showed that the preferential constraint of destabilizing joint angle variance was the putative mechanism underlying performance. This thesis performed a detailed examination of unstable object control mechanisms. The undertaken studies have provided knowledge about the acquisition and adaptation of control mechanisms at multiple levels of the motor system. Our data provide convergent evidence that the control mechanisms governing complex human balancing tasks are intermittent and modulated by the task and context.Doctor of Philosophy (PhD
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