Modulation of ipsilateral motor evoked potentials during bimanual coordination tasks

IntroductionIpsilateral motor evoked potentials (iMEPs) are difficult to obtain in distal upper limb muscles of healthy participants but give a direct insight into the role of ipsilateral motor control.MethodsWe tested a new high-intensity double pulse transcranial magnetic stimulation (TMS) protocol to elicit iMEPs in wrist extensor and flexor muscles during four different bimanual movements (cooperative—asymmetric, cooperative—symmetric, non-cooperative—asymmetric and non-cooperative—symmetric) in 16 participants.ResultsNine participants showed an iMEP in the wrist extensor in at least 20% of the trials in each of the conditions and were classified as iMEP+ participants. iMEP persistence was greater for cooperative (50.5 ± 28.8%) compared to non-cooperative (31.6 ± 22.1%) tasks but did not differ between asymmetric and symmetric tasks. Area and amplitude of iMEPs were also increased during cooperative (area = 5.41 ± 3.4 mV × ms; amplitude = 1.60 ± 1.09 mV) compared to non-cooperative (area = 3.89 ± 2.0 mV × ms; amplitude = 1.12 ± 0.56 mV) tasks and unaffected by task-symmetry.DiscussionThe upregulation of iMEPs during common-goal cooperative tasks shows a functional relevance of ipsilateral motor control in bimanual movements. The paired-pulse TMS protocol is a reliable method to elicit iMEPs in healthy participants and can give new information about neural control of upper limb movements. With this work we contribute to the research field in two main aspects. First, we describe a reliable method to elicit ipsilateral motor evoked potentials in healthy participants which will be useful in further advancing research in the area of upper limb movements. Second, we add new insight into the motor control of bimanual movements. We were able to show an upregulation of bilateral control represented by increased ipsilateral motor evoked potentials in cooperative, object-oriented movements compared to separate bimanual tasks. This result might also have an impact on neurorehabilitation after stroke

Proactive modulation of long-interval intracortical inhibition during response inhibition

Daily activities often require sudden cancellation of preplanned movement, termed response inhibition. When only a subcomponent of a whole response must be suppressed (required here on Partial trials), the ensuing component is markedly delayed. The neural mechanisms underlying partial response inhibition remain unclear. We hypothesized that Partial trials would be associated with nonselective corticomotor suppression and that GABA(B) receptor-mediated inhibition within primary motor cortex might be responsible for the nonselective corticomotor suppression contributing to Partial trial response delays. Sixteen right-handed participants performed a bimanual anticipatory response inhibition task while single- and paired-pulse transcranial magnetic stimulation was delivered to elicit motor evoked potentials in the left first dorsal interosseous muscle. Lift times, amplitude of motor evoked potentials, and long-interval intracortical inhibition were examined across the different trial types (Go, Stop-Left, Stop-Right, Stop-Both). Go trials produced a tight distribution of lift times around the target, whereas those during Partial trials (Stop-Left and Stop-Right) were substantially delayed. The modulation of motor evoked potential amplitude during Stop-Right trials reflected anticipation, suppression, and subsequent reinitiation of movement. Importantly, suppression was present across all Stop trial types, indicative of a “default” nonselective inhibitory process. Compared with blocks containing only Go trials, inhibition increased when Stop trials were introduced but did not differ between trial types. The amount of inhibition was positively correlated with lift times during Stop-Right trials. Tonic levels of inhibition appear to be proactively modulated by task context and influence the speed at which unimanual responses occur after a nonselective “brake” is applied

Aproximaciones metodológicas a la investigación en artes

La ciencia, entendida como saber científico, puede definirse como una forma de llegar al conocimiento. Pero ¿qué es realmente y cómo iniciarse en esta forma de trabajo? Este artículo expone algunas estrategias y orientaciones sobre cómo elaborar y planificar una investigación en artes, atendiendo a las actividades y conocimientos necesarios para desarrollarla. El objetivo principal es ayudar al estudiante que se dispone a dar sus primeros pasos en el camino de la investigación, por lo que se abordan algunas de las cuestiones más comunes entre los investigadores nóveles y que, con frecuencia, presentan dificultades notables, tales como: cuáles son los tipos de investigaciones en este ámbito, el posicionamiento teórico a adoptar por parte del investigador; la elección de una metodología o el procedimiento para recogida y análisis de datos, entre otras. Science, as a scientific knowledge, can be defined as a means to reach knowledge. Nevertheless, what is it actually and how can I get started with this work method? This article shows some strategies and orientations about elaborating and planning art investigations by paying attention to those activities and knowledge that are necessary to develop it. The main scope is helping the student who is trying to take their first steps in the investigation field; thus, some of the most frequent questions among novel investigators will be approached. In many occasions, these issues cause difficulties, such as: the type of investigations that can be found in this field; the theoretical position to be adopted by the investigator; or the selection of a method or a procedure to collect and analyse data, among many other

Uncoupling response inhibition

The ability to prevent unwanted movement is fundamental to human behavior. When healthy adults must prevent a subset of prepared actions, execution of the remaining response is markedly delayed. We hypothesized that the delay may be sensitive to the degree of similarity between the prevented and continued actions. Fifteen healthy participants performed an anticipatory response inhibition task that required bilateral index finger extension or thumb abduction with homogeneous digit pairings, or a heterogeneous pairing of a combination of the two movements. We expected that the uncoupling of responses required for selective movement prevention would be more difficult with homogeneous (same digit, homologous muscles) than heterogeneous pairings (different digits, nonhomologous muscles). Measures of response times (and asynchrony between digits) during action execution, stopping performance, and electromyography from EIP (index finger extension) and APB (thumb abduction) were analyzed. As expected, selective trials produced a delay in the remaining movement compared with execution trials. Successful performance in the selective condition occurred via suppression of the entire prepared response and subsequent selective reinitiation of the remaining component. Importantly, the delayed reinitiation of motor output was sensitive to the degree of similarity between responses, occurring later but at a faster rate with homogeneous digits. There were persistent aftereffects from the selective condition on the motor system, which indicated greater levels of inhibition and a higher gain were necessary to successfully perform selective trials with homogeneous pairings. Overall, the results support a model of inhibition of a unitary response and selective reinitiation, rather than selective inhibition. </jats:p

Lymphoproliferation und Antigenspezifität von Lymphozyten frisch manifestierter Typ I Diabetiker gegen die Proteine Bovines Serum Albumin und Beta-Casein sowie Insulin

Ziel dier Arbeit war der Nachweis T-Lymphozyten, die spezifisch auf in der Nahrung vorkommende bzw. körpereigene Antigene reagieren, sowie die Bildung antigenspezifischer T-Zelllinien.Es wurde dabei untersucht, ob Unterschiede in Lyphoproliferation und Antigenspezifität zwischen frisch manifestierten Typ I Diabetikern sowie gesunden Kontrollpersonen nachweisbar sind.Nach der Isolation von Lymphozyten aus dem peripher venösen Blut der Probanden erfolgte die Kultivierung der Zellen mit den verschiedenen Antigenen sowie Tetanol als Kontrolle. Es folgten 5-7 Stimulationen mit Interleukin-2, im Anschluß daran der Test auf antigenspezifische Proliferation. Dabei wurden die Zellen der generierten Linien erneut mit ihren jeweiligen Antigenen kultiviert, nach 56 h radioaktiv markiert und nach 72 h geerntet. Die intrazelluläre Radioaktivität wurde gemessen, und galt als ein Maß für die Proliferationsaktivität der Zellen. Weiterhin wurde ein Proliferationsindex gebildet als Maß für die antigenspezifische Proliferation.Beim Vergleich zwischen den Gruppen ergaben sich keine signifikannten Unterschiede. Typ I Diabetiker wiesen tendeziell die höhere Lymphoproliferatin auf.The aim of this study was T-lymphocytes, specific for cow´s milk antigens and insulin, and the generation of antigen specific T-cellines.Furhtermore was tried to give evidence for differences in lymphoproliferation and antigen specificity between newly diagnosed patients with type I diabetes and healthy controls.After isolation of lymphocytes from peripheral blood, they were cocultered with the investigated antigens BSA, Casein and insulin, tetanol was used as control; followed by 5-7 stimulations with interleukin-2.After this generation of T-cellines the test for antigen specific proliferation was assesed.The generated t-cells were cultured again with the specific antigen, marked with a radioactive amino acid, and harvested after 72 h. The incorporated radioactivity was the expression for lymphoproliferation. To determine antigen specific proliferation the proliferation index was developed.The results of the tested groups were compared. No significant differebces were found. Type I diabetic patinets seem to express higher activity of T-lymphocytes

PREP2 Algorithm Predictions Are Correct at 2 Years Poststroke for Most Patients

Background. The PREP2 algorithm combines clinical and neurophysiological measures to predict upper-limb (UL) motor outcomes 3 months poststroke, using 4 prediction categories based on Action Research Arm Test (ARAT) scores. The algorithm was accurate at 3 months for 75% of participants in a previous validation study. Objective. This study aimed to evaluate whether PREP2 predictions made at baseline are correct 2 years poststroke. We also assessed whether patients’ UL performance remained stable, improved, or worsened between 3 months and 2 years after stroke. Methods. This is a follow-up study of 192 participants recruited and assessed in the original PREP2 validation study. Participants who completed assessments 3 months poststroke (n = 157) were invited to complete follow-up assessments at 2 years poststroke for the present study. UL outcomes were assessed with the ARAT, upper extremity Fugl-Meyer Scale, and Motor Activity Log. Results. A total of 86 participants completed 2-year follow-up assessments in this study. PREP2 predictions made at baseline were correct for 69/86 (80%) participants 2 years poststroke, and PREP2 UL outcome category was stable between 3 months and 2 years poststroke for 71/86 (83%). There was no difference in age, stroke severity, or comorbidities among patients whose category remained stable, improved, or deteriorated. Conclusions. PREP2 algorithm predictions made within days of stroke are correct at both 3 months and 2 years poststroke for most patients. Further investigation may be useful to identify which patients are likely to improve, remain stable, or deteriorate between 3 months and 2 years

The fall and rise of corticomotor excitability with cancellation and reinitiation of prepared action

The sudden cancellation of a motor action, known as response inhibition (RI), is fundamental to human motor behavior. The behavioral selectivity of RI can be studied by cueing cancellation of only a subset of a planned response, which markedly delays the remaining executed components. The present study examined neurophysiological mechanisms that may contribute to these delays. In two experiments, human participants received single- and paired-pulse transcranial magnetic stimulation while performing a bimanual anticipatory response task. Participants performed most trials bimanually (Go trials) and were sometimes cued to cancel the response with one hand while responding with the other (Partial trials). Motor evoked potentials were recorded from left first dorsal interosseous (FDI) as a measure of corticomotor excitability (CME) during Go and Partial trials. CME was temporally modulated during Partial trials in a manner that reflected anticipation, suppression, and subsequent initiation of a reprogrammed response. There was an initial increase in CME, followed by suppression 175 ms after the stop signal, even though the left hand was not cued to stop. A second increase in excitability occurred prior to the (delayed) response. We propose an activation threshold model to account for nonselective RI. To investigate the inhibitory component of our model, we investigated short-latency intracortical inhibition (sICI), but results indicated that sICI cannot fully explain the observed temporal modulation of CME. These neurophysiological and behavioural results indicate that the default mode for reactive partial cancellation is suppression of a unitary response, followed by response reinitiation with an inevitable time delay. </jats:p

Response inhibition activates distinct motor cortical inhibitory processes

We routinely cancel preplanned movements that are no longer required. If stopping is forewarned, proactive processes are engaged to selectively decrease motor cortex excitability. However, without advance information there is a nonselective reduction in motor cortical excitability. In this study we examined modulation of human primary motor cortex inhibitory networks during response inhibition tasks with informative and uninformative cues using paired-pulse transcranial magnetic stimulation. Long- (LICI) and short-interval intracortical inhibition (SICI), indicative of GABAB- and GABAA-receptor mediated inhibition, respectively, were examined from motor evoked potentials obtained in task-relevant and task-irrelevant hand muscles when response inhibition was preceded by informative and uninformative cues. When the participants (10 men and 8 women) were cued to stop only a subcomponent of the bimanual response, the remaining response was delayed, and the extent of delay was greatest in the more reactive context, when cues were uninformative. For LICI, inhibition was reduced in both muscles during all types of response inhibition trials compared with the pre-task resting baseline. When cues were uninformative and left-hand responses were suddenly canceled, task-relevant LICI positively correlated with response times of the responding right hand. In trials where left-hand responding was highly probable or known (informative cues), task-relevant SICI was reduced compared with that when cued to rest, revealing a motor set indicative of responding. These novel findings indicate that the GABAB-receptor-mediated pathway may set a default inhibitory tone according to task context, whereas the GABAA-receptor-mediated pathways are recruited proactively with response certainty. NEW &amp; NOTEWORTHY We examined how informative and uninformative cues that trigger both proactive and reactive processes modulate GABAergic inhibitory networks within human primary motor cortex. We show that GABAB inhibition was released during the task regardless of cue type, whereas GABAA inhibition was reduced when responding was highly probable or known compared with rest. GABAB-receptor-mediated inhibition may set a default inhibitory tone, whereas GABAA circuits may be modulated proactively according to response certainty. </jats:p

The excitability of ipsilateral motor evoked potentials is not task-specific and spatially distinct from the contralateral motor hotspot

Objective The role of ipsilateral descending motor pathways in voluntary movement of humans is still a matter of debate. Few studies have examined the task dependent modulation of ipsilateral motor evoked potentials (iMEPs). Here, we determined the location of upper limb biceps brachii (BB) representation within the ipsilateral primary motor cortex. Methods MR-navigated transcranial magnetic stimulation mapping of the dominant hemisphere was undertaken with twenty healthy participants who made tonic unilateral, bilateral homologous or bilateral antagonistic elbow flexion-extension voluntary contractions. Map center of gravity (CoG) and area for each BB were obtained. Results The map CoG of the ipsilateral BB was located more anterior-laterally than those of the contralateral BB within the primary motor cortex. However different tasks had no effect on either the iMEP CoG location or the size. Conclusion Our data suggests that ipsilateral and contralateral MEP might originate in distinct adjacent neural populations in the primary motor cortex, independent of task dependence