1,721,498 research outputs found
Repetitive transcranial magnetic stimulation or transcranial direct current stimulation?
No full textIn recent years two techniques have become available to stimulate the human brain noninvasively through the scalp: repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS). Prolonged application of either method (eg, several hundred TMS pulses [rTMS] or several minutes of tDCS) leads to changes in excitability of the cortex that outlast the period of stimulation. Because of this, besides the implications for experimental neuroscientists, there is increasing interest in the potential for applying either method as a therapy in neurology, psychiatry, rehabilitation, and pain. Given that both techniques lead to the same final result, this article discusses in theory several issues that can help an investigator to decide whether rTMS or tDCS would be more suitable for the scope of the planned work. (C) 2009 Elsevier Inc
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
SOME SACCADIC EYE-MOVEMENTS CAN BE DELAYED BY TRANSCRANIAL MAGNETIC STIMULATION OF THE CEREBRAL-CORTEX IN MAN
No full textIn 15 normal subjects we investigated the effect on visually guided saccadic eye movements of giving a single transcranial magnetic stimulus through a circular coil centred at the vertex. In the normal paradigm, subjects fixated a target which moved randomly to the left or right by 11-degrees. The mean saccadic reaction time of 189 ms was increased by 40 - 50 ms if a magnetic stimulus was given in random trials some 60 ms prior to the expected onset time of control saccades. The duration and amplitude of the saccades was unchanged. The delay was smaller if the stimulus was given earlier in the reaction period, or if the coil was moved anterior or posterior to the vertex. Larger stimulus intensities produced longer delays. Three subjects were trained to produce express saccades (mean saccadic reaction times of 107 - 141 ms) in a 'gap' paradigm. The latency of these saccades, which are thought to be mediated by collicular mechanisms without involvement of the cortex, was not affected by magnetic stimulation. This suggests that magnetic stimulation delays normal visually guided saccades by an action on the cerebral cortex, rather than on the oculomotor centres of the brainstem. Five subjects made nontargeted saccades in darkness in response to an auditory stimulus. These saccades, like visually guided saccades, could be delayed by magnetic brain stimulation. We conclude that saccadic delay is produced by interference with cortical areas involved in the execution of saccades rather than by interfering with the perception of the visual or auditory 'go' stimulus. These probably include supplementary and frontal eye field and posterior parietal cortex. The fact that visually guided saccades emerged intact after the delay indicates that the instructions for amplitude and direction were stored separately from those involved in timing when the movement was to occur
CORTICAL PROJECTION TO ERECTOR SPINAE MUSCLES IN MAN AS ASSESSED BY FOCAL TRANSCRANIAL MAGNETIC STIMULATION
No full textWe stimulated the motor cortex in 9 subjects using focal transcranial magnetic stimulation with a figure of 8 coil in order to examine the cortical representation of the erector Spinae muscles. Recordings were made from the erector spinae 3.5 cm lateral to the third lumbar vertebra. In 5 subjects clearly reproducible responses could be obtained which had a latency compatible with transmission via fast conducting fibers in a mono- or oligosynaptic pathway. In the remaining 4 subjects responses were poorly defined. Latencies in surface recordings varied between 13 and 24 msec but were longer when needle recordings were used. Mapping of the motor cortex was performed by moving the coil in 2 cm steps on either side of Cz. Different patterns of hemispheric representation were found ranging from a contralateral projection in either hemisphere to a representation of both back muscles in one hemisphere (2 subjects). Responses were followed by a silent period. The latter was interrupted orterminated by a response between 52 and 85 msec post stimulus which was found predominantly in the muscle ipsilateral to the side of stimulation
EVIDENCE THAT TRANSCRANIAL MAGNETIC STIMULATION DELAYS SACCADIC EYE-MOVEMENTS BY INTERFERING WITH ACTIVITY IN OCULOMOTOR AREAS OF CORTEX IN MAN
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Inhibitory action of forearm flexor muscle afferents on corticospinal outputs to antagonist muscles in humans
No full text1. To find out whether muscle afferents influence the excitability of corticospinal projections to antagonist muscles, we studied sixteen healthy subjects and one patient with a focal brain lesion. 2. Using transcranial magnetic and electrical brain stimulation we tested the excitability of corticomotoneuronal connections to right forearm muscles at rest after conditioning stimulation of the median nerve at the elbow. Somatosensory potentials evoked by median nerve stimulation were also recorded in each subject. 3. Test stimuli delivered at 13-19 ms after median nerve stimulation significantly inhibited EMG responses elicited in forearm extensor muscles by transcranial magnetic stimulation, but did not inhibit responses to electrical stimulation. In contrast, magnetically and electrically elicited responses in forearm flexor muscles were suppressed to the same extent. 4. The higher the intensity of the test shocks, the smaller was the amount of median nerve-elicited inhibition. Inhibition in extensor muscles was also smaller during tonic wrist extension, or if the induced electrical stimulating current in the brain flowed from posterior to anterior over the motor strip rather than vice versa. Test responses evoked by magnetic transcranial stimulation in the first dorsal interosseous and in brachioradialis muscles were not inhibited after median nerve stimulation at the elbow. Stimulation of digital nerves failed to inhibit motor potentials in extensor muscles. 5. Test stimuli delivered at 15 and 17 ms after radial nerve stimulation significantly inhibited EMG responses elicited in forearm flexor muscles by magnetic transcranial stimulation. 6. In the patient with a focal thalamic lesion, who had dystonic postures and an absent N20 component of the somatosensory-evoked potentials but normal strength, median nerve stimulation failed to inhibit magnetically evoked responses in forearm extensor muscles. 7. We propose that activation of median nerve muscle afferents can suppress the excitability of cortical areas controlling the antagonist forearm extensor muscles acting on the hand. The inhibitory effect occurs at short latency and might assist spinal pathways mediating reciprocal inhibition by contrasting the co-activation of antagonistic pools of corticospinal cells
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