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Role of the cerebellum in externally paced rhythmic finger movements
No full textSeveral studies have suggested that the
cerebellum has an important role in timing of subsecond intervals.
Previous studies using transcranial magnetic stimulation (TMS) to test
this hypothesis directly have produced inconsistent results. Here we
used 1-Hz repetitive TMS (rTMS) for 10 min over the right or left
cerebellar hemisphere to interfere transiently with cerebellar processing to assess its effect on the performance of a finger-tapping task.
Subjects tapped with their right index finger for 1 min (synchronization phase) with an auditory or visual cue at 0.5, 1, or 2 Hz; they
continued for a further 1 min at the same rate with no cues (continuation phase). The blocks of trials were performed in a random order.
rTMS of the cerebellum ipsilateral to the movement increased the
variability of the intertap interval but only for movements at 2 Hz that
were made while subjects were synchronizing with an auditory cue.
There was no effect on the continuation phase of the task when the
cues were no longer present or on synchronization with a visual cue.
Similar results were seen after stimulation over the contralateral
dorsal premotor cortex but not after rTMS over supplementary motor
area. There was no effect after rTMS over the ipsilateral right cervical
nerve roots or over the ipsilateral primary motor cortex. The results
support the hypothesis of neural network for event-related timing in
the subsecond range that involves a cerebellar-premotor network
Functional interplay between posterior parietal and ipsilateral motor cortex revealed by twin-coil transcranial magnetic stimulation during reach planning toward contralateral space
No full textPosterior parietal cortex (PPC) has connections with motor and premotor cortex, thought to transfer information relevant for planning
movements in space. We used twin-coil transcranial magnetic stimulation (tcTMS) methods to show that the functional interplay
between human right PPC and ipsilateral motor cortex (M1) varies with current motor plans. tcTMS during the reaction time of a reach
task revealed facilitatory influences of right PPC on right M1 only when planning a (contralateral) leftward rather than rightward reach,
attwo specifictime intervals (50 and 125 ms) after an auditory cue. The earlier reach-direction-specificfacilitatory influencefrom PPC on
M1 occurred when subjects were blindfolded or when the targets were presented briefly, so that visual feedback corrections could not
occur. PPC–M1 interplay was similar withinthe left hemisphere but was specificto (contralateral) rightward planned reaches, with peaks
at 50 and 100 ms. Functional interplay between human parietal and motor cortex is enhanced during early stages of planning a reach in
the contralateral directio
Time course of functional connectivity between dorsal premotor and contralateral motor cortex during movement selection
No full textThe left dorsal premotor cortex (PMd) is thought to play a dominant role in the selection of movements made by either hand. We used
transcranial magnetic stimulation to study the functional connectivity of the left PMd and right primary motor cortex (M1) during an
acoustic choice reaction time (RT) task involving contraction of the thumb and forefinger. The facilitatory and inhibitory pathways that
can be demonstrated between left PMd and right M1 at rest were suppressed during most of the reaction period. However, they were
activated briefly at the start of the reaction period, depending on whether the cue indicated that the forthcoming movement had to be
made withthe left orthe right hand. Thefacilitatory pathway was active at 75msinthosetrialsin whichthe subjects were requiredtomove
the left hand, whereastheinhibitory pathway was active at 100 msintrialsin whichthe subjects hadto movethe right hand. These changes
in excitability did not occur in hand muscles not used in the task. There were no significant changes in the excitability of intracortical
circuits [short intracortical inhibition (SICI) and intracortical facilitation (ICF)] in the right M1. Interhemispheric interactions between
the right PMd and left M1 were mainly inhibitory at rest and showed the same temporal profile of interhemispheric inhibition as for left
PMd–right M1, although no evidence was found for facilitatory interactions. The results illustrate the importance of PMd not only in
facilitating cued movements but also in suppressing movements that have been prepared but are not use
Focal stimulation of the posterior parietal cortex increases the excitability of the ipsilateral motor cortex
No full textPaired-pulse transcranial magnetic stimulation (TMS) has been applied as a probe to test functional connectivity within distinct cortical
areas ofthe human motor system. Here, wetestedthe interaction betweenthe posterior parietal cortex (PPC) and ipsilateral motor cortex
(M1). A conditioning TMS pulse over the right PPC potentiates motor evoked-potentials evoked by a test TMS pulse over the ipsilateral
motor cortex, with a time course characterized by two phases: an early peak at 4 ms interstimulus interval (ISI) and a late peak at 15 ms
ISI. Activation of this facilitatory pathway depends on the intensity of stimulation, because the effects are induced with a conditioning
stimulus of 90% resting motor threshold but not at lower or higher intensities. Similar results were obtained testing the ipsilateral
interaction inthe left hemisphere with a slightly differenttime course. In control experiments, wefoundthat activation ofthisfacilitatory
pathway depends on the direction of induced current in the brain and is specific for stimulation of the caudal part of the inferior parietal
sulcus (cIPS) site, because it is not observed for stimulation of adjacent scalp sites. Finally, we found that by using poststimulus time
histogram analysis of single motor unit firing, the PPC conditioning increases the excitability of ipsilateral M1, enhancing the relative
amount of late I wave input recruited by the test stimulus over M1, suggesting that such interaction is mediated by specific interneurons
in the motor cortex. The described facilitatory connections between cIPS and M1 may be important in a variety of motor tasks and
neuropsychiatric disorder
Altered dorsal premotor-motor interhemispheric pathway activity in focal arm dystonia
No full textGiven the possible role of dorsal premotor cortex(PMd) in the pathophysiology of dystonia, we used transcranialmagnetic stimulation (TMS) methods to study PMd and PMd–primary motor cortex (M1) interactions in patients with focalarm dystonia. Here, we tested the connectivity between leftPMd and right M1 as well as the intracortical excitability ofPMd in 11 right-handed patients with focal arm/hand dystoniaand nine age-matched healthy controls. The results showed thatexcitability of the inhibitory connection between PMd and M1was reduced in patients, but there was no significant differenceto healthy subjects in the excitability of the facilitatory con-nection. A triple stimulation technique in which pairs of TMSpulses are given over PMd and their interaction measured interms of the effect on the baseline PMd-M1 connection failedto reveal the usual pattern of interaction between the pairs ofPMd stimuli. Indeed, the results in patients were similar tothose seen in a group of young healthy subjects after theexcitability of PMd had been changed by pretreatment withhigh-frequency rTMS. We suggest that reduced transcallosalinhibition from the PMd may be involved in the altered patternof abnormal muscle contractions of agonists and antagonists(overflow
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
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