1,721,073 research outputs found
Improving EEG source analysis using prior knowledge.
No full textItem does not contain fulltextKUN, 02 juli 2003Promotores : Oosterom, A. van, Stegeman, D.F. Co-promotor : Praamstra, P
Feeling the beat: the neurophysiology of cueing in Parkinson's disease
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199080.pdf (Publisher’s version ) (Open Access)Radboud University, 18 januari 2019Promotor : Bloem, B.R. Co-promotores : Praamstra, P., Lange, F.P. d
Absence of gaze direction effects on EEG measures of sensorimotor function
No full textObjective: Gaze direction is known to modulate the activation patterns of sensorimotor areas as seen at the single cell level and in functional magnetic resonance imaging (fMRI). To determine whether such gaze direction effects can be observed in scalp-recorded electroencephalogram (EEG) measures of sensorimotor function we investigated somatosensory evoked potentials (SEPs) and steady state movement related cortical potentials (MRPs).Methods: In two separate experiments, SEPs were elicited by electrical stimulation of the median nerve (experiment 1) and steady state MRPs were induced by 2 Hz tapping paced by an auditory cue (experiment 2), while subjects directed their gaze 15° to the left or to the right.Results: Gaze direction failed to produce any appreciable differences in the waveforms of the SEPs or MRPs. In particular, there was no effect on peak amplitude, peak latency and peak scalp topography measures of SEP and MRP components, or on spatial or temporal parameters of dipole models of the underlying cortical generators. Additional frequency domain analyses did not reveal reliable gaze-related changes in induced power at electrode sites overlying somatosensory and motor areas, or in coherence between pairs of parietal, central and frontal electrodes, across a broad range of frequencies.Conclusions: EEG measures of sensorimotor function, obtained in a non-visual motor task, are insensitive to modulatory effects of gaze direction in sensorimotor areas that are observable with fMRI
Proprioceptive sensory function in Parkinson's disease and Huntington's disease: evidence from proprioception-related EEG potentials
No full textIn both Parkinson's disease and Huntington's disease, proprioceptive sensory deficits have been suggested to contribute to the motor manifestations of the disease. Here, proprioceptive sensory function was investigated in Parkinson's disease patients, Huntington's disease patients, and healthy control subjects (each group n=8), using proprioception-related evoked potentials. Proprioception-related potentials were elicited by passive index finger movements and measured with high-density EEG. Conventional median nerve somatosensory evoked potentials (mnSEPs) were recorded in the same session. Analysis included amplitude and latency measures from selected scalp electrodes and dipole source reconstruction. We found a proprioception-related N90 component of normal latency in both Parkinson's disease and Huntington's disease. The source strength of the underlying cortical generator was normal in Parkinson's disease, but marginally reduced in Huntington's disease. Using the source location of the N20-P20 component of the mnSEP as a landmark for postcentral area 3b, the N90 was localized to the precentral motor cortex. At a latency around 170-180 ms proprioception-related potentials were explained by bilateral sensory cortex activation with an altered distribution in Parkinson's disease and a reduction of ipsilateral activation in Huntington's disease. Together, the results show largely normal early proprioception-related potentials, but changes in the cortical processing of kinaesthetic signals at longer latencies in both diseases
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
Proprioception-related evoked potentials: origin and sensitivity to movement parameters
No full textReafferentelectroencephalography (EEG) potentials evoked by active or passive movement are largely dependent on muscle spindle input, which projects to postrolandic sensory areas as well as the precentral motor cortex. The origin of these proprioception-related evoked potentials has previously been studied by using N20-P20 source locations of the median nerve somatosensory evoked potential as an landmark for postcentral area 3b. As this approach has yielded contradictory findings, likely due to spatial undersampling, we applied dipole source analysis on two independently collected sets of high-density EEG data, containing the proprioception-related N90 elicited by passive finger movement, and the N20-P20 elicited by median nerve stimulation. In addition, the influence of movement parameters on the N90 was explored by varying amplitude/duration and direction of passive movements. The results showed that the proprioceptive N90 component was not influenced by movement direction, but had a duration that covaried with the duration of the movement. Sources were localized in the precentral cortex, located on average 10 mm anterior to the N20-P20 sources. The latter result supports earlier claims that the motor cortex is involved in the generation of proprioception-related EEG potentials
Time-course of masked response priming and inhibition in Parkinson's disease
No full textParkinson's disease patients have enhanced interference effects arising from the conflict between competing responses, as probed in various 'conflict tasks'. The possibility that this is due to an inhibitory deficit received recent support from a masked response priming task [Seiss, E., & Praamstra, P. (2004). The basal ganglia and inhibitory mechanisms in response selection: Evidence from subliminal priming of motor responses in Parkinson's disease. Brain, 127, 330-339]. The added information from a masked priming task is that the introduction of a delay between presentation of prime and target stimuli reveals an inhibition of the covert response activation induced by the masked prime stimulus. This inhibition results in a reversal of normal priming effects, such that performance is better with incompatible than with compatible prime-target pairs. We previously found that this reversal is attenuated in Parkinson's disease, when tested at a prime-target delay of 100 ms, thus revealing deficient inhibition of covert response activation. The present study was undertaken to investigate the time course of the underlying inhibition process, using five prime-target ISIs between 0 and 200 ms. While we reproduced the attenuation at ISI 100 ms, the time course information revealed that the rate of change of the compatibility effect over ISIs from 0 to 200 ms was identical for patients and controls. This result indicates that the inhibition underlying the reversal of masked priming effects is normal in Parkinson's disease
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