A method to estimate EMG crosstalk between two muscles based on the silent period following an H-reflex

The crosstalk phenomenon consists in recording the volume-conducted electromyographic activity of muscles other than that under study. This interference may impair the correct interpretation of the results in a variety of experiments. A new protocol is presented here for crosstalk assessment between two muscles based on changes in their electrical activity following a reflex discharge in one of the muscles in response to nerve stimulation. A reflex compound muscle action potential (H-reflex) was used to induce a silent period in the muscle that causes the crosstalk, called here the remote muscle. The rationale is that if the activity recorded in the target muscle is influenced by a distant source (the remote muscle) a silent period observed in the electromyogram (EMG) of the remote muscle would coincide with a decrease in the EMG activity of the target muscle. The new crosstalk index is evaluated based on the root mean square (RMS) values of the EMGs obtained in two distinct periods (background EMG and silent period) of both the remote and the target muscles. In the present work the application focused on the estimation of the degree of crosstalk from the soleus muscle to the tibialis anterior muscle during quiet stance. However, the technique may be extended to other pairs of muscles provided a silent period may be evoked in one of them. (C) 2009 IPEM. Published by Elsevier Ltd. All rights reserved.

Excitability changes in human forearm corticospinal projections and spinal reflex pathways during rhythmic voluntary movement of the opposite limb

Rhythmic movements brought about by the contraction of muscles on one side of the body give rise to phase-locked changes in the excitability of the homologous motor pathways of the opposite limb. Such crossed facilitation should favour patterns of bimanual coordination in which homologous muscles are engaged simultaneously, and disrupt those in which the muscles are activated in an alternating fashion. In order to examine these issues, we obtained responses to transcranial magnetic stimulation (TMS), to stimulation of the cervicomedullary junction (cervicomedullary-evoked potentials, CMEPs), to peripheral nerve stimulation (H-reflexes and f-waves), and elicited stretch reflexes in the relaxed right flexor carpi radialis (FCR) muscle during rhythmic (2 Hz) flexion and extension movements of the opposite (left) wrist. The potentials evoked by TMS in right FCR were potentiated during the phases of movement in which the left FCR was most strongly engaged. In contrast, CMEPs were unaffected by the movements of the opposite limb. These results suggest that there was systematic variation of the excitability of the motor cortex ipsilateral to the moving limb. H-reflexes and stretch reflexes recorded in right FCR were modulated in phase with the activation of left FCR. As the f-waves did not vary in corresponding fashion, it appears that the phasic modulation of the H-reflex was mediated by presynaptic inhibition of Ia afferents. The observation that both H-reflexes and f-waves were depressed markedly during movements of the opposite indicates that there may also have been postsynaptic inhibition or disfacilitation of the largest motor units. Our findings indicate that the patterned modulation of excitability in motor pathways that occurs during rhythmic movements of the opposite limb is mediated primarily by interhemispheric interactions between cortical motor areas.

The effects of prepulse-blink reflex trial repetition and prepulse change on blink reflex modification at short and long lead intervals

Prepulse inhibition and facilitation of the blink reflex are said to reflect different responses elicited by the lead stimulus, transient detection and orienting response respectively. Two experiments investigated the effects of trial repetition and lead stimulus change on blink modification. It was hypothesized that these manipulations will affect orienting and thus blink facilitation to a greater extent than they will affect transient detection and thus blink inhibition. In Experiment 1 (N = 64), subjects were trained with a sequence of 12 lead stimulus and 12 blink stimulus alone presentations, and 24 lead stimulus-blink stimulus pairings. Lead interval was 120 ms for 12 of the trials and 2000 ms for the other 12. For half the subjects this sequence was followed by a change in pitch of the lead stimulus. In Experiment 2 (N = 64), subjects were trained with a sequence of 36 blink alone stimuli and 36 lead stimulus-blink stimulus pairings. The lead interval was 120 ms for half the subjects and 2000 ms for the other half. The pitch of the lead stimulus on prestimulus trials 31-33 was changed for half the subjects in each group. In both experiments, the amount of blink inhibition decreased during training whereas the amount of blink facilitation remained unchanged. Lead stimulus change had no effect on blink modification in either experiment although it resulted in enhanced skin conductance responses and greater heart rate deceleration in Experiment 2. The present results are not consistent with the notion that blink facilitation is linked to orienting whereas blink inhibition reflects a transient detection mechanism. (C) 1998 Elsevier Science B.V.

The effect of repeated prepulse and reflex stimulus presentations on startle prepulse inhibition

The magnitude of a startle reflex is inhibited if the reflex-eliciting stimuli is preceded by a prepulse stimulus at a short lead interval. Previous research in humans has shown that the extent of prepulse inhibition decreases over repeated presentations of reflex stimuli and prepulse-reflex stimulus pairings. The present study (N=70) investigated the effect of repeated presentations of prepulse stimuli, reflex stimuli, or prepulse-reflex stimulus pairings on prepulse inhibition. Five groups of subjects were presented during habituation training with either (a) reflex stimuli, (b) prepulse-reflex stimulus pairings, (c) a random sequence of prepulse and reflex stimuli, (d) prepulse stimuli, or (e) experimentally irrelevant light stimuli. Prepulse inhibition was reduced if startle stimuli were presented during habituation ((a), (b), (c)), but not after repeated presentation of the prepulse or the light stimulus ((d), (e)). The reduction in prepulse inhibition was abolished after dishabituation of the startle reflex. The present results indicate that habituation of the startle reflex can result in a reduction of prepulse inhibition. (C) 1998 Elsevier Science B.V.

H-reflex modulation during passive lengthening and shortening of the human triceps surae

1. The present study investigated the effects of lengthening and shortening actions on IT-reflex amplitude. H-reflexes were evoked in the soleus (SOL) and medial gastroenemius (MG) of human subject, during passive isometric, lengthening and shortening actions performed at angular velocities of 0, +/-2, +/-5 and +/- 15 deg s(-1). 2. H-reflex amplitude, in froth SOL and MG were significantly depressed during passive lengthening actions and facilitated during passive shortening actions, when compared with the isometric R-reflex amplitude. 3. Four experiments were performed in which the latencies front the onset of movement to delivery of the stimulus were altered. Passive H-reflex modulation during lengthening actions was found tee begin at latencies of less than 60 ms suggesting that this inhibition was due to peripheral and/or spinal mechanisms. 4. It is postulated that, the H-reflex modulation seen in the present study is related to the tunic discharge of muscle spindle afferents and the consequent effects of transmission within the la pathway. Inhibition of the H-reflex at less than 60 ms after the onset of muscle lengthening may he attributed to several mechanisms, which cannot be distinguished using the current protocol. These may include the inability to evoke volleys in la fibres that are refractory following muscle spindle discharge during; rapid muscle lengthening, a reduced probability of transmitter release front the presynaptic terminal (homosynaptic post.-activation depression) and presynaptic inhibition of la afferents from plantar flexor agonists. Short latency facilitation of the H-reflex may be attributed to temporal summation of excitatory postsynaptic potentials arising from muscle spindle afferents during rapid muscle lengthening. At longer latencies, presynaptic inhibition of Ia afferents cannot be excluded as a potential inhibitory mechanism.

Attentional modulation of the startle reflex during threat of shock

The present study (N532) investigated attentional modulation of the startle blink reflex at long lead intervals under conditions of differing emotional valence. Participants performed a visual discrimination and counting task while coloured lights indicated whether it was possible for the participant to receive an electrotactile shock (threat of shock) or if no shock would be presented (safe). Latency and magnitude of startle responses to probes during inter-stimulus intervals were facilitated during threat periods relative to safe periods. Startle latency and magnitude modulation were enhanced during attended discrimination and counting task stimuli relative to startle during ignored stimuli. This attention effect did not vary under threat or safe conditions, suggesting that attentional startle modulation is not affected by the emotional valence of the context.

Catheter ablation of severe neurally meditated reflex (neurocardiogenic or vasovagal) syncope: cardioneuroablation long-term results

Aims Neurally meditated reflex or neurocardiogenic or vasovagal syncope (NMS) is usually mediated by a massive vagal reflex. This study reports the long-term outcome of NMS therapy based on endocardial radiofrequency (RF) catheter ablation of the cardiac vagal nervous system aiming permanent attenuation or elimination of the cardioinhibitory reflex (cardioneuroablation). Methods and results A total of 43 patients (18F/25M, 32.9+/-15 years) without apparent cardiopathy (left ventricular ejection fraction=68.6+/-5%) were included. All had recurrent NMS (4.7+/-2 syncope/patient) with important cardioinhibition (pauses=13.5+/-13 s) at head-up tilt test (HUT), normal electrocardiogram (ECG), and normal atropine test (AT). The patients underwent atrial endocardial RF ablation using spectral mapping to track the neurocardiac interface (AF Nest Mapping). The follow-up (FU) consisted of clinical evaluation, ECG (1 month/every 6 months/or symptoms), Holter (every 6 months/or symptoms), HUT (>= 4 months/or symptoms), and AT (end of ablation and >= 6 months). A total of 44 ablations (48+/-9 points/patient) were performed. Merely three cases of spontaneous syncope occurred in 45.1+/-22 months (two vasodepressor, one undefined). Only four partial cardioinhibitory responses occurred in post-ablation HUT without pauses or asystole (sinus bradycardia). Long-term AT (21.7+/-11 months post) was negative in 33 (76.7%, P<0.01), partially positive in 7(16.3%), and normal in three patients only (6.9%) reflecting long-term vagal denervation (AT-Delta% HR pre 79.4% x 23.2% post). The post-ablation stress test and Holter showed no abnormalities. No major complications occurred. Conclusion Endocardial RF catheter ablation of severe neurally meditated reflex syncope prevented pacemaker implantation and showed excellent long-term results in well selected patients. Despite no action in vasodepression it seems to cause enough long-term vagal reflex attenuation, eliminating the cardioinhibition, and keeping most patients asymptomatic. Indication was based on clinical symptoms, reproduction of severe cardioinhibitory syncope, and normal atropine response.

Modeling upper eyelid kinematics during spontaneous and reflex blinks

To test a mathematical model for measuring blinking kinematics. Spontaneous and reflex blinks of 23 healthy subjects were recorded with two different temporal resolutions. A magnetic search coil was used to record 77 blinks sampled at 200 Hz and 2 kHz in 13 subjects. A video system with low temporal resolution (30 Hz) was employed to register 60 blinks of 10 other subjects. The experimental data points were fitted with a model that assumes that the upper eyelid movement can be divided into two parts: an impulsive accelerated motion followed by a damped harmonic oscillation. All spontaneous and reflex blinks, including those recorded with low resolution, were well fitted by the model with a median coefficient of determination of 0.990. No significant difference was observed when the parameters of the blinks were estimated with the under-damped or critically damped solutions of the harmonic oscillator. On the other hand, the over-damped solution was not applicable to fit any movement. There was good agreement between the model and numerical estimation of the amplitude but not of maximum velocity. Spontaneous and reflex blinks can be mathematically described as consisting of two different phases. The down-phase is mainly an accelerated movement followed by a short time that represents the initial part of the damped harmonic oscillation. The latter is entirely responsible for the up-phase of the movement. Depending on the instantaneous characteristics of each movement, the under-damped or critically damped oscillation is better suited to describe the second phase of the blink. (C) 2010 Elsevier B.V. All rights reserved.

Anticipation of a non-aversive reaction time task facilitates the blink startle reflex

The conditions under which blink startle facilitation can be found in anticipation of a reaction time task were investigated to resolve inconsistent findings across previous studies. Four groups of participants (n = 64) were presented with two visual stimuli, one predicting a reaction time task (S+) and the second presented alone (S-). Participants were asked to make a speeded response to the offset of the S+ (S1 paradigm) or were asked to respond to a tactile stimulus presented at the offset of the S+ (S1-S2 paradigm). Half of the participants in each paradigm condition received performance feedback. Overall, blink latency shortening and magnitude facilitation were larger during S+ than during S-. More detailed analyses, however, found these differences to be reliable only in the Feedback conditions. Ratings of S+ pleasantness did not change across the experiment. Electrodermal responses to S+ were larger than to S- in all groups with differential electrodermal responding emerging earlier in the S1 paradigm. Taken together, the data support the notion that startle facilitation can occur during non-aversive Pavlovian conditioning. (C) 2002 Elsevier Science B.V. All rights reserved.

Lead stimulus modality change and the attentional modulation of the acoustic and electrical blink reflex

Two experiments investigated the effects of the sensory modality of the lead and of the blink-eliciting stimulus during lead stimulus modality change on blink modulation at lead intervals of 2500 and 3500 ins. Participants were presented with acoustic, visual, or tactile change stimuli after habituation training with lead stimuli from the same or a different sensory modality. In Experiment 1, latency and magnitude of the acoustic blink were facilitated during a change to acoustic or visual lead stimuli, but not during a change to tactile lead stimuli. After habituation to acoustic lead stimuli, blink magnitude was smaller during tactile change stimuli than during habituation stimuli. The latter finding was replicated in Experiment 2 in which blink was elicited by electrical stimulation of the trigeminal nerve. The consistency of the findings across different combinations of lead stimulus and blink-eliciting stimulus modalities does not support a modality-specific account of attentional blink modulation. Rather, blink modulation during generalized orienting reflects modality non-specific processes, although modulation may not always be found during tactile lead stimuli. (C) 2002 Elsevier Science B.V. All rights reserved.

Projeto b??sico: oficina de reflex??o e alinhamento das pol??ticas de promo????o e incentivo ?? leitura em nosso pa??s

Contrata????o de servi??os t??cnicos profissionais especializados de doc??ncia para modera????o na Oficina, sob medida, de reflex??o e alinhamento das pol??ticas de promo????o e incentivo ?? leitura em nosso Pa??s, sendo a execu????o da Oficina norteada pelas diretrizes expressas no inciso I do art. 2?? da Resolu????o n?? 01 de 31 de janeiro de 2013 e nos incisos I do art. 2?? do Decreto n?? 8.091, de 03 de setembro de 2013

Texto para discuss??o 3: Reflex??es sobre a proposta de reforma do Estado brasileiro

A reforma do Estado ?? uma preocupa????o comum a quase todos os pa??ses do mundo. No ??mbito nacional, ap??s um per??odo mais exacerbado de radicaliza????es e polariza????es, o debate sobre o assunto vem adquirindo maior serenidade, profundidade e rigor. Seu foco tem se deslocado de uma defini????o aprior??stica e descontextualizada do tamanho ideal do Estado (e, com isso, vem conseguindo, paulatinamente, ultrapassar os manique??smos iniciais), para se centrar em quest??es realmente estrat??gicas: que tipo de Estado se deseja construir? Como dever?? se relacionar com a sociedade e o mercado? Quais ser??o sua miss??o, objetivos, papel, formas e meios de interven????o e fun????es? Que caracter??sticas organizacionais e gerenciais necessitar?? adquirir para lograr ??xito? O primeiro volume desta s??rie ?? um exemplo dessa mudan??a oportuna de enfoque, partindo do Estado necess??rio e conseguindo avan??ar em rela????o a, pelo menos, algumas das quest??es estrat??gicas j?? mencionadas

Texto para discuss??o 6: a tecnologia da informa????o na reforma do Estado: uma reflex??o sobre os dilemas e perspectivas para as grandes empresas de processamento de dados da ??rea p??blica

O presente texto procura focalizar mais especificamente a quest??o dos modelos organizacionais adotados pelas empresas p??blicas de processamento de dados, e sua poss??vel reestrutura????o para fazer frente ??s novas necessidades de seus usu??rios, em meio a mudan??as profundas nas plataformas tecnol??gicas tradicionalmente adotadas. A inten????o ?? contribuir para que o debate iniciado tenha prosseguimento, pela relev??ncia desse tema para a reforma do aparelho estatal ora em andamento no pa??s, tanto em n??vel federal quanto no ??mbito de Estados e munic??pios

Reflex??es para Ibero-Am??rica: avalia????o de programas sociais

A ENAP Escola Nacional de Administra????o P??blica, com o apoio do Minist??rio do Planejamento, Or??amento e Gest??o, da Ag??ncia Brasileira de Coopera????o do Minist??rio das Rela????es Exteriores, do Centro Latino-americano de Administra????o para o Desenvolvimento (Clad) e da Caixa Econ??mica Federal, construiu uma s??rie de atividades de aprendizagem direcionadas a dirigentes e t??cnicos que atuam nas ??reas de planejamento estrat??gico e avalia????o de programas. Esses eventos de aprendizagem permitiram uma intensa troca de experi??ncias entre os 60 dirigentes e t??cnicos representantes de organismos governamentais de 16 pa??ses ibero-americanos ??? Argentina, Bol??via, Brasil, Chile, Col??mbia, Costa Rica, El Salvador, Guatemala, M??xico, Panam??, Paraguai, Peru, Portugal, Rep??blica Dominicana, Uruguai e Venezuela. A consolida????o desse per??odo de rica troca de experi??ncias est?? retratada nesta publica????o, que mostra o avan??o na constru????o de um conhecimento coletivo referente a desafios contempor??neos de nossos governos nas ??reas de planejamento e de avalia????o de programas sociais