1,721,186 research outputs found
Combining muscle-computer interface guided training with bihemispheric tDCS improves upper limb function in patients with chronic stroke
No full textTranscranial direct current stimulation (tDCS) may facilitate neuroplasticity but with a limited effect when administered while patients with stroke are at rest. Muscle-computer interface (MCI) training is a promising approach for training patients with stroke even if they cannot produce overt movements. However, using tDCS to enhance MCI training has not been investigated. We combined bihemispheric tDCS with MCI training of the paretic wrist and examined the effect of this intervention in patients with chronic stroke. A crossover, double-blind, randomized trial was conducted. Twenty-six patients with chronic stroke performed MCI wrist training for three consecutive days at home while receiving either real tDCS or sham tDCS in counterbalanced order and separated by at least 8 mo. The primary outcome measure was the Fugl-Meyer Assessment Upper Extremity Scale (FMA-UE) that was measured 1 wk before training, on the first training day, on the last training day, and 1 wk after training. There was neither a significant difference in the baseline FMA-UE score between groups nor between intervention periods. Patients improved 3.9 +/- 0.6 points in FMA-UE score when receiving real tDCS, and 1.0 +/- 0.7 points when receiving sham tDCS (P = 0.003). In addition, patients also showed continuous improvement in their motor control of the MCI tasks over the training days. Our study showed that the training paradigm could lead to functional improvement in patients with chronic stroke. We argue that appropriate MCI training in combination with bihemispheric tDCS could be a useful adjuvant for neurorehabilitation in patients with stroke.Flanders Fund for Scientific Research [G. 0758.10]; ETH Zurich; Nationa
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
Heart–Brain Interactions in the MR Environment: Characterization of the Ballistocardiogram in EEG Signals Collected During Simultaneous fMRI
No full textThe ballistocardiographic (BCG) artifact is linked to cardiac activity and occurs in electroencephalographic (EEG) recordings acquired inside the magnetic resonance (MR) environment. Its variability in terms of amplitude, waveform shape and spatial distribution over subject’s scalp makes its attenuation a challenging task. In this study, we aimed to provide a detailed characterization of the BCG properties, including its temporal dependency on cardiac events and its spatio-temporal dynamics. To this end, we used high-density EEG data acquired during simultaneous functional MR imaging in six healthy volunteers. First, we investigated the relationship between cardiac activity and BCG occurrences in the EEG recordings. We observed large variability in the delay between ECG and subsequent BCG events (ECG–BCG delay) across subjects and non-negligible epoch-by-epoch variations at the single subject level. The inspection of spatial–temporal variations revealed a prominent non-stationarity of the BCG signal. We identified five main BCG waves, which were common across subjects. Principal component analysis revealed two spatially distinct patterns to explain most of the variance (85% in total). These components are possibly related to head rotation and pulse-driven scalp expansion, respectively. Our results may inspire the development of novel, more effective methods for the removal of the BCG, capable of isolating and attenuating artifact occurrences while preserving true neuronal activity
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
Sensorimotor cortical processing of back pain-related stimuli in patients with chronic lower back pain and healthy controls
No full textKarakteristieken van het humane spiegelsysteem Activiteitsmetingen in de primaire motorische cortex aan de hand van transcraniale magnetische stimulatie
No full textDuring the past decade, neuroscience has increasingly focused on the rol e of the so-called mirror system in a variety of functions such as act ion recognition, action understanding, and imitation. Mirror neurons wer e initially discovered in the ventral premotor cortex of the macaque bra in and have the striking property to discharge not only when the monkey performs an action, but also when it merely observes a similar action pe rformed by another individual. To study the human mirror system at work during action perception, transcranial magnetic stimulation (TMS) has pr oven to be an excellent technique, as it can be used to obtain fast and focal measurements of cortical activity within the primary motor area (M 1) of subjects observing actions performed by others. In the present doc toral project, the TMS technique is extensively used to investigate whet her and how the mirror system is responsive to action observation. To do so, different parameters of perceived actions are manipulated to assess their relative importance in mediating resonant activity in the obser vers motor system. When a voluntary action is generated, the brain must encode the directio n of the movement in space, specified in an external coordinate frame, a nd translate this directional information into a set of muscle activatio n patterns, specified in an intrinsic coordinate frame. From single cell recordings in monkeys, it was shown that M1 contains both direction-rel ated and muscle-related neurons to a nearly equal extent. However, it re mains largely unclear which of the two reference frames is used during t he process of observation-to-execution mapping. To address this question , our first study adopted a paradigm from which it was possible to disen tangle whether the observers primary motor cortex is facilitated in acc ordance to either the observed movement direction or the observed muscle activation. Overall, data indicated that the mirror system, at least at the level of M1, reflects the muscular requirements of observed actions , rather than the directional features. Based on the findings of our first study (i.e., muscle specific activity modulations at the level of M1 during movement observation) and the not ion that observation-induced reactivation of motor areas may have a posi tive impact on recovery of motor functions after stroke, the second stud y aimed to identify the most effective observation settings that mediate muscle specific facilitation of the motor system during action observat ion. More specifically, we explored the effects of varying body configur ations between the observer and observed model on observation-induced ac tivity in M1. Overall, it was shown that activity within the mirror syst em may depend substantially upon the laterality of the observed hand (i. e., left or right) and the perspective from which the action is observed (i.e., first or third person perspective). More specifically, facilitat ion of the observers M1 was shown to be particularly high when right ha nd actions were observed from a first person perspective, whereas, for l eft hand actions, the third person perspective was more efficient. On th e other hand, the degree of postural congruency between body parts of th e observer and observed model only mildly influenced the extent of M1 fa cilitation. Overall, the results of these first two studies indicated that M1 activi ty is strongly driven by a muscle-specific mapping between the observed movement and the observers motor system. This raised the question wheth er the mirror system and, particularly M1, encodes also other parameters related to the muscular requirements of the observed movement, such as the produced force. This hypothesis was tested in the third and fourth s tudy of the project. Overall, data indicated that observation-induced ac tivity in M1 reflects the level of observed grip force when subjects obs erve the lifting of different object weights. Moreover, the encoding of grip force requirements in M1 appeared to be mediated by distinct visual cues of the observed lifting actions, such as the associated kinematica l profile as well as the muscle tension/pressure produced in the acting hand. Surprisingly, object-related information on object weight (and con sequently on exerted grip force) appeared to have only minor influences on the encoding of force within M1. Finally, the focus shifted slightly in the last study in which we invest igated how different types of sensory input drive the human mirror syste m. Although it has been shown that the mirror system responds to either action-specific vision or sound, it remains a topic of debate whether mi rror activity reflects multisensory convergence of vision and sound during action perception. To address this question, M1 activity w as measured while subjects perceived unimodal visual (V), unimodal audit ory (A), or multimodal (V + A) stimuli of a simple hand action. In short , data indicated that perception-induced activity in M1 increases substa ntially from the simultaneous presentation of visual and auditory input about a perceived action. As such, these data speak in favour of multimo dal audio-visual action representations in the human motor system. In summary, the present doctoral project provides novel insights on the process of observation-to-execution mapping within motor areas by measur ing observation-induced activity modulations at the level of the primary motor cortex. More specifically, our data support the hypothesis that M 1 may contribute to action observation, by representing the muscle-relat ed features of observed actions. The application of movement observation in motor rehabilitation is theor etically based on the finding that cortical motor circuits are activated in a similar way during movement observation as during execution. Incre asing our insights into the visual features that actually mediate activi ty modulations in the motor system during movement perception may theref ore help to identify the most effective conditions for stimulating the m otor system during action observation.status: Publishe
Hemisferische asymmetrieën van de premotorische en primaire motorische cortex in motorische controle aangetoond door "virtuele laesie" TMS
No full textIt is generally known that the cortical motor system of each hemisphere controls the movements executed with the contralateral body side, such that left motor areas control the right body side, while the right motor areas control the left body side. Interestingly, the primary motor cortex (M1) seems to be also activated when movements are executed with the ipsilateral hand. In this doctoral project, we have used several transcranial magnetic stimulation (TMS) paradigms to investigate which potential mechanisms underlie this ipsilateral facilitation of motor areas. Our first study showed that the cortical excitability in M1 increased when the ipsilateral hand performed rhythmical flexion-extension movements. This facilitation increased further when movements were performed in the context of a complex coordination task requiring that wrist and ankle were moved rhythmically into opposite directions. Furthermore, the facilitation revealed a hemispheric asymmetry, such that more facilitation was seen in the left M1 when the left body side was activated than in the right M1 when a movement was executed with the right body side. We corroborated these findings with our second study using a virtual lesion approach. This TMS technique allows to test a causal relationship of a specific cortical area and a specific behavior. Subjects had to produce an unimanual tapping task while disruptive TMS was applied to the ipsilateral M1. In right handed subjects, more disruptions of the tapping task were observed when left than when right M1 was stimulated, showing that particularly the left ipsilateral M1 is involved in unimanual digit control. However, in left handed subjects we observed two subgroups, such that half of the left handed subjects exhibited more disruptions when the ipsilateral left hemisphere was stimulated while the other half showed more disruptions when the ipsilateral right hemisphere was stimulated. Overall, we showed that the important role of the ipsilateral M1 in unimanual movements is influenced by handedness as well as (left) hemispheric specialization.The potential mechanisms underlying the functional lateralization of the ipsilateral M1 can emerge at different levels of the nervous system. Hemispheric asymmetries of the ipsilateral M1 could either reflect asymmetries in direct uncrossed corticospinal fibers or in transcallosal pathways suggesting that the left M1 has a stronger influence on the right M1 than vice versa. We tried to directly test the second hypothesis, but found no support for the notion that hemispheric asymmetries arise predominantly via transcallosal pathways. Based on our results, we speculate that hemispheric asymmetries might arise from areas upstream from M1, such as the premotor cortex. To test this hypothesis, we explored asymmetries of the premotor involvement in coordination movements using a virtual lesion approach. In our third study we tested lateralization of the dorsal premotor cortex (PMd) during bimanual movements, and found more disruptions of a complex bimanual coordination patternwhen the right PMd than when the left PMd was stimulated. Moreover, this asymmetry was influenced by handedness, as left handed subjects were more frequently disrupted when the non-dominant left PMd was stimulated. In the last study, we applied TMS in a virtual lesion approach over the ventral (PMv) and dorsal (PMd) premotor cortex while right-handed subjects performed either a bimanual coordination task or unimanual movement with the hand ipsilateral to the stimulated hemisphere. We found that particularly the PMv exhibited hemispheric asymmetries in ipsilateral unimanual movements, such that the left PMv was stronger involved in the control of movements executed with the left hand than the right PMv in right handed movements. Moreover, this asymmetry was not seen in the PMd, although we demonstrated the same lateralization as in the 3rd study (i.e. more disruptions when right than when left PMd was stimulated). Overall, we suggest that the left PMv primarily influences the ipsilateral M1 to control movements of the ipsilateral left hand, while the right PMd primarily regulates the transcallosal effects on the non-dominant right M1 to prevent unwanted mirror movements.In summary, the present PhD thesis provides novel insights into the role of the hemisphere ipsilateral to the moving hand. We have demonstrated that the involvement of the ipsilateral motor areas exhibits hemispheric asymmetries which depend on the task that is executed, the investigated motor area and the subjects handedness.status: Publishe
Centrale representatiestructuur van interledematen coördinatiepatronen: analyse van gedrag en hersenactiviteit
No full textstatus: Publishe
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