Neuromuscular electrical stimulation (NMES) has become an increasingly popular rehabilitative treatment approach for swallowing disorders (dysphagia). However, its precise effects on swallowing biomechanics and measures of swallowing neurophysiology are unclear. Clearly defined NMES treatment protocols that have been corroborated by thorough empirical research are lacking. The primary objective of this research programme was therefore to establish optimal NMES treatment parameters for the anterior hyo-mandibular (submental) musculature, a muscle group that is critically involved in the oral and pharyngeal phases of swallowing. Based on previous research, the primary hypothesis was that various NMES treatment protocols would have differential effects of either enhancing or inhibiting the excitability of corticobulbar projections to this muscle group. The research paradigm used to test this hypothesis was an evaluation of MEP amplitude and onset latency, recorded in the functional context of volitional contraction of the submental musculature (VC) and contraction of this muscle group during the pharyngeal phase of volitional swallowing (VPS, volitional pharyngeal swallow). Outcome measures were recorded before and at several time points after each NMES treatment trial. This methodology is similar to, but improved upon, research paradigms previously reported. Changes in corticobulbar excitability in response to various NMES treatment protocols were recorded in a series of experiments. Ten healthy research participants were recruited into a study that evaluated the effects of event-related NMES, whereas 15 healthy research participants were enrolled in a study that investigated the effects of non-event-related NMES. In a third cohort of 35 healthy research participants, task-dependent differences in corticobulbar excitability were evaluated during three conditions of submental muscle contraction: VC, VPS and submental muscle contraction during the pharyngeal phase of reflexive swallowing (RPS, reflexive pharyngeal swallowing). Event-related NMES induced frequency-depended changes in corticobulbar excitability. NMES administered at 80 Hz facilitated MEP amplitude, whereas NMES at 5 Hz and 20 Hz inhibited MEP amplitude. No changes were observed after NMES at 40 Hz. Maximal excitatory or inhibitory changes occurred 60 min post-treatment. Changes in MEP amplitude in response to event-related NMES were only observed when MEPs were recorded during the VC condition, whereas MEPs recorded during the VPS condition remained unaffected. Non-event-related NMES did not affect MEP amplitude in either of the muscle contraction conditions. Similarly, MEP onset latencies remained unchanged across all comparisons. MEPs were detected most consistently during the VC contraction condition. They were less frequently detected and were smaller in amplitude for the VPS condition and they were infrequently detected during pre-activation by RPS. The documented results indicate that event-related NMES has a more substantial impact on MEP amplitude than non-event-related NMES, producing excitatory and inhibitory effects. Comparison of MEPs recorded during VC, VPS and RPS suggests that different neural networks may govern the motor control of submental muscle activation during these tasks. This research programme is the first to investigate the effects of various NMES treatment protocols on the excitability of submental corticobulbar projections. It provides important new information for the use of NMES in clinical rehabilitation practices and our understanding of the neural networks governing swallowing motor control.

Neuromuscular electrical stimulation (NMES) has become an increasingly popular rehabilitative treatment approach for swallowing disorders (dysphagia). However, its precise effects on swallowing biomechanics and measures of swallowing neurophysiology are unclear. Clearly defined NMES treatment protocols that have been corroborated by thorough empirical research are lacking. The primary objective of this research programme was therefore to establish optimal NMES treatment parameters for the anterior hyo-mandibular (submental) musculature, a muscle group that is critically involved in the oral and pharyngeal phases of swallowing. Based on previous research, the primary hypothesis was that various NMES treatment protocols would have differential effects of either enhancing or inhibiting the excitability of corticobulbar projections to this muscle group. The research paradigm used to test this hypothesis was an evaluation of MEP amplitude and onset latency, recorded in the functional context of volitional contraction of the submental musculature (VC) and contraction of this muscle group during the pharyngeal phase of volitional swallowing (VPS, volitional pharyngeal swallow). Outcome measures were recorded before and at several time points after each NMES treatment trial. This methodology is similar to, but improved upon, research paradigms previously reported. Changes in corticobulbar excitability in response to various NMES treatment protocols were recorded in a series of experiments. Ten healthy research participants were recruited into a study that evaluated the effects of event-related NMES, whereas 15 healthy research participants were enrolled in a study that investigated the effects of non-event-related NMES. In a third cohort of 35 healthy research participants, task-dependent differences in corticobulbar excitability were evaluated during three conditions of submental muscle contraction: VC, VPS and submental muscle contraction during the pharyngeal phase of reflexive swallowing (RPS, reflexive pharyngeal swallowing). Event-related NMES induced frequency-depended changes in corticobulbar excitability. NMES administered at 80 Hz facilitated MEP amplitude, whereas NMES at 5 Hz and 20 Hz inhibited MEP amplitude. No changes were observed after NMES at 40 Hz. Maximal excitatory or inhibitory changes occurred 60 min post-treatment. Changes in MEP amplitude in response to event-related NMES were only observed when MEPs were recorded during the VC condition, whereas MEPs recorded during the VPS condition remained unaffected. Non-event-related NMES did not affect MEP amplitude in either of the muscle contraction conditions. Similarly, MEP onset latencies remained unchanged across all comparisons. MEPs were detected most consistently during the VC contraction condition. They were less frequently detected and were smaller in amplitude for the VPS condition and they were infrequently detected during pre-activation by RPS. The documented results indicate that event-related NMES has a more substantial impact on MEP amplitude than non-event-related NMES, producing excitatory and inhibitory effects. Comparison of MEPs recorded during VC, VPS and RPS suggests that different neural networks may govern the motor control of submental muscle activation during these tasks. This research programme is the first to investigate the effects of various NMES treatment protocols on the excitability of submental corticobulbar projections. It provides important new information for the use of NMES in clinical rehabilitation practices and our understanding of the neural networks governing swallowing motor control.

The reticular-activating hypofrontality model of acute exercise (RAH) predicts exercise-induced hypoactivity in frontal cortex which mediates executive function. Connors Continuous Performance Test (CCPT) was used to investigate changes in executive function during- and post treadmill running in healthy volunteers (n=30, 15 male). In a randomized order, subjects performed the CCPT at rest, during low- (LI; 63% maximal heart rate; MHR) and moderate intensity (MI; 75% MHR). Separately, subjects then performed isocalorifically matched exercise bouts of LI, MI and high intensity interval training (HIT) consisting of 4x4 min with 90% MHR and 3 min recovery at 60-70% MHR. Repeated measures ANOVAs revealed main effects of exercise intensity for reaction time RT during- (p≤0.001) and post exercise (p≤0.0001). Subsequent analyses showed an overall increase of RT during exercise compared to rest (p≤0.005). RT decreased significantly from rest to post exercise levels in an exercise intensity dependent, linear fashion (p≤0.0001). Commission errors showed a non significant linear trend to increase both during (p=0.057), and post exercise (p=0.052) as a function of intensity. In a follow up study, we sought to relate observed exercise effects to frontal cortex activity through the use of transcranial direct current stimulation (tDCS) (n=4) and transcranial magnetic stimulation (TMS) over the dorsolateral prefrontal cortex (DLPFC). Prior to TMS stimulation cortical excitability was estimated post running through motor-evoked potentials (MEP) elicited from the primary motor cortex (M1) induced by single burst TMS and measured in the first dorsal interosseous (FDI) muscle using electromyography. At rest, inhibitory cathodal tDCS with left DLPFC cathode and right supraorbital anode led to improved reaction time and increased amount of commission errors, whereas anodal stimulatory tDCS in the immediate post exercise period was unable to recover the post exercise effect. Continuous theta burst stimulation over the left DLPFC post running further impaired inhibitory control and facilitated reaction time. Different findings during- and after- exercise suggests that potential contributing mechanisms such as computational and metabolic factors may be differentially active during these respective conditions. Furthermore, the fact that an inhibitory TMS protocol pronounced the post running effects even more and that we were able to mimic the reported RAH effects at rest with inhibitory frontal tDCS, but observed different patterns during exercise, suggests that the latter state cannot be fully explained by reducing activity in the left frontal cortex alone. Failure to modify the after exercise effect with stimulatory tDCS also supports an interplay of different factors and might emphasize the strong, robust effects of exercise that cannot simply be attenuated by current application. Increases in MEP post running for 35min paired with the observed performance decrements imply an excited state of M1 and might serve as an explanatory cross-link to central fatigue suggesting that a hypofrontal state might enhance the motor cortical drive to activate muscles.

Transcranial magnetic stimulation (TMS) is a 37-year-old non-invasive tool and can be used for diagnostic, therapeutics, and research purposes. In research, TMS is mostly used to stimulate the motor cortex, resulting in a neuroelectric excitatory response called a motor evoked potential (MEP). The resulting nerve signal leads to muscle movement, which can be measured by electromyography (EMG). Majority of previous research has targeted muscles of the upper limbs, due to the relative inaccessibility of the cortical leg area. Thus, the aim of this study is to investigate whether asymmetry occurs during lower limb stimulation and if there is a difference in stimulated muscles between dominant and non-dominant leg. Nine healthy adults conducted cortical stimulation over the motor cortex using double cone coil. EMG was recorded from the rectus femoris, tibialis anterior and abductor hallucis on both left and right leg. Depending on the subject's tolerance, data was collected by delivering 30 or 35 pulses. For each intensity, five MEPs were recorded, starting at 30% of the intensity and increasing in steps of 10%. Results showed no significant difference (p>0,05) between the dominant and non-dominant leg in all three muscles. In conclusion, the study no stimulus response asymmetry between the dominant and non-dominant leg in the respective muscle.

O potencial evocado motor facial (PEMF) tem-se mostrado um excelente método de monitorização do nervo facial, gerando resultados bastante confiáveis e reprodutíveis no que tange à predição da função facial pós-operatória. O critério eletrofisiológico mais utilizado até então para tanto tem sido a relação de amplitude do PEMF final-valor de base. Os objetivos deste trabalho foram avaliar as alterações intraoperatórias da amplitude e da complexidade do PEMF, correlacioná-las com o prognóstico facial no pós-operatório imediato e tardio e verificar se amplitude e complexidade constituem variáveis independentes de predição funcional. Os registros dos potenciais intraoperatórios dos músculos orbiculares do olho e da boca de 35 pacientes portadores de schwannoma vestibular (SV) foram coletados e analisados retrospectivamente de acordo com tempos cirúrgicos preestabelecidos: inicial, abertura da dura-máter, dissecação do tumor (TuDis), ressecção do tumor (TuRes) e final. No pós-operatório imediato, a função facial apresentou uma significativa correlação negativa com as relações de amplitude do PEMF durante a TuDis, a TuRes e ao final do procedimento nos músculos orbiculares do olho (p =0,003, 0,055 e 0,028, respectivamente) e da boca (p=0,002, 0,104 e 0,014, respectivamente). No último seguimento, entretanto, a correlação foi significativa apenas para o músculo orbicular da boca, durante a TuDis (p=0,005) e ao final do procedimento (p=0,102). As variações da complexidade dos potenciais alcançaram resultados mais significativos tanto no pós-operatório imediato, quanto no tardio, de forma que houve uma correlação negativa no músculo orbicular do olho apenas nas medidas finais (imediato, p=0;023; seguimento, p=0,116) e no músculo orbicular da boca durante a TuDis, a TuRes e a medida final (imediato, p=0,071, 0,000 e 0,001, respectivamente; seguimento, p=0,015, 0,001 e 0,01, respectivamente). As alterações intraoperatórias das relações de amplitude e de complexidade dos PEMFs parecem representar variáveis independentes, podendo ser utilizadas na predição da função facial pós-operatória durante cirurgias de ressecção de SV. Baseados nos resultados deste trabalho, a monitorização evento-valor de base é bastante útil, justificando mudanças imediatas da estratégia cirúrgica, com o intuito de reduzir as chances de uma lesão definitiva do nervo facial. / Facial motor evoked potential (FMEP) amplitude ratio reduction at the end of the surgery has been identified as a good predictor for postoperative facial nerve outcome. We sought to investigate variations in FMEP amplitude and waveform morphology during vestibular schwannoma (VS) resection and to correlate these measures with postoperative facial function immediately after surgery and at the last follow-up. Besides we analyzed the relationship between quantitative parameters. Intraoperative orbicularis oculi and oris muscles FMEP data from 35 patients undergoing surgery for VS resection were collected, then analyzed by surgical stage: initial, dural opening, tumor dissection (TuDis), tumor resection (TuRes) and final. Immediately after surgery, postoperative facial function correlated significantly with the FMEP amplitude ratio during TuDis, TuRes and final in both the orbicularis oculi (p´s=0.003, 0.055 and 0.028, respectively) and oris muscles (p´s=0.002, 0.104 and 0.014, respectively). At the last follow-up, however, facial function correlated significantly with the FMEP amplitude ratio only during TuDis (p=0.005) and final (p=0.102) for the orbicularis oris muscle. At both time points, postoperative facial paresis correlated significantly with FMEP waveform deterioration in orbicularis oculi during final (immediate, p=0.023; follow-up, p=0.116) and in orbicularis oris during TuDis, TuRes and final (immediate, p´s=0.071, 0.000 and 0.001, respectively; follow-up, p´s=0.015, 0.001 and 0.01, respectively). FMEP amplitude ratio and waveform morphology during VS resection seem to represent independent quantitative parameters that can be used to predict postoperative facial function. Event-to-baseline FMEP monitoring is quite useful to dictate when intraoperative changes in surgical strategy are warranted to reduce chances of facial nerve injury.

Cortical representations are plastic and are allocated based on the proportional use or disuse of a pathway. A steady stream of sensory input maintains the integrity of cortical networks; while in contrast, alterations in afferent activation promote sensorimotor reorganization. After an incomplete spinal cord injury (SCI), damage to the ascending and/or descending pathways induces widespread modifications to the sensorimotor system. Strengthening these spared sensorimotor pathways may be therapeutic by promoting functional recovery after injury. Using a technique called transcranial magnetic stimulation (TMS), we show that the leg motor cortex is facilitated by peripheral sensory inputs via disinhibition and potentiation of excitatory intracortical circuits. Hence, in addition to its crucial role in sensory perception, excitation from peripheral sensory afferents can reinforce muscle activity by engaging, and possibly shaping, the activity of the human motor cortex. After SCI, the amount of excitation produced by afferent stimulation reaching the motor cortex is expectantly reduced and delayed. This reduction of sensory inflow to the motor cortex may contribute to our findings that cortical inhibition is down-regulated after SCI, and this compensation may aid in the recruitment of excitatory networks in the motor cortex as a result of the damage to its output neurons. By repeatedly pairing sensory inputs from a peripheral nerve in the leg with direct cortical activation by TMS, in an intervention called paired associative stimulation, we show that the motor system can be potentiated in both uninjured individuals and after SCI. In the uninjured subjects, we show that in order to produce associative facilitation, the time window required for coincident activation of the motor cortex by TMS and peripheral sensory inputs is not as narrow as previously thought (~100 vs. ~20 ms), likely due to the persistent activation of cortical neurons following activation by TMS. The potential to condition the nervous system with convergent afferent and cortical inputs suggests that paired associative stimulation may serve as a priming tool for motor plasticity and rehabilitation following SCI.

No description available.

O potencial evocado motor facial (PEMF) tem-se mostrado um excelente método de monitorização do nervo facial, gerando resultados bastante confiáveis e reprodutíveis no que tange à predição da função facial pós-operatória. O critério eletrofisiológico mais utilizado até então para tanto tem sido a relação de amplitude do PEMF final-valor de base. Os objetivos deste trabalho foram avaliar as alterações intraoperatórias da amplitude e da complexidade do PEMF, correlacioná-las com o prognóstico facial no pós-operatório imediato e tardio e verificar se amplitude e complexidade constituem variáveis independentes de predição funcional. Os registros dos potenciais intraoperatórios dos músculos orbiculares do olho e da boca de 35 pacientes portadores de schwannoma vestibular (SV) foram coletados e analisados retrospectivamente de acordo com tempos cirúrgicos preestabelecidos: inicial, abertura da dura-máter, dissecação do tumor (TuDis), ressecção do tumor (TuRes) e final. No pós-operatório imediato, a função facial apresentou uma significativa correlação negativa com as relações de amplitude do PEMF durante a TuDis, a TuRes e ao final do procedimento nos músculos orbiculares do olho (p =0,003, 0,055 e 0,028, respectivamente) e da boca (p=0,002, 0,104 e 0,014, respectivamente). No último seguimento, entretanto, a correlação foi significativa apenas para o músculo orbicular da boca, durante a TuDis (p=0,005) e ao final do procedimento (p=0,102). As variações da complexidade dos potenciais alcançaram resultados mais significativos tanto no pós-operatório imediato, quanto no tardio, de forma que houve uma correlação negativa no músculo orbicular do olho apenas nas medidas finais (imediato, p=0;023; seguimento, p=0,116) e no músculo orbicular da boca durante a TuDis, a TuRes e a medida final (imediato, p=0,071, 0,000 e 0,001, respectivamente; seguimento, p=0,015, 0,001 e 0,01, respectivamente). As alterações intraoperatórias das relações de amplitude e de complexidade dos PEMFs parecem representar variáveis independentes, podendo ser utilizadas na predição da função facial pós-operatória durante cirurgias de ressecção de SV. Baseados nos resultados deste trabalho, a monitorização evento-valor de base é bastante útil, justificando mudanças imediatas da estratégia cirúrgica, com o intuito de reduzir as chances de uma lesão definitiva do nervo facial. / Facial motor evoked potential (FMEP) amplitude ratio reduction at the end of the surgery has been identified as a good predictor for postoperative facial nerve outcome. We sought to investigate variations in FMEP amplitude and waveform morphology during vestibular schwannoma (VS) resection and to correlate these measures with postoperative facial function immediately after surgery and at the last follow-up. Besides we analyzed the relationship between quantitative parameters. Intraoperative orbicularis oculi and oris muscles FMEP data from 35 patients undergoing surgery for VS resection were collected, then analyzed by surgical stage: initial, dural opening, tumor dissection (TuDis), tumor resection (TuRes) and final. Immediately after surgery, postoperative facial function correlated significantly with the FMEP amplitude ratio during TuDis, TuRes and final in both the orbicularis oculi (p´s=0.003, 0.055 and 0.028, respectively) and oris muscles (p´s=0.002, 0.104 and 0.014, respectively). At the last follow-up, however, facial function correlated significantly with the FMEP amplitude ratio only during TuDis (p=0.005) and final (p=0.102) for the orbicularis oris muscle. At both time points, postoperative facial paresis correlated significantly with FMEP waveform deterioration in orbicularis oculi during final (immediate, p=0.023; follow-up, p=0.116) and in orbicularis oris during TuDis, TuRes and final (immediate, p´s=0.071, 0.000 and 0.001, respectively; follow-up, p´s=0.015, 0.001 and 0.01, respectively). FMEP amplitude ratio and waveform morphology during VS resection seem to represent independent quantitative parameters that can be used to predict postoperative facial function. Event-to-baseline FMEP monitoring is quite useful to dictate when intraoperative changes in surgical strategy are warranted to reduce chances of facial nerve injury.

Il existe plusieurs théories du contrôle moteur, chacune présumant qu’une différente variable du mouvement est réglée par le cortex moteur. On trouve parmi elles la théorie du modèle interne qui a émis l’hypothèse que le cortex moteur programme la trajectoire du mouvement et l’activité électromyographique (EMG) d’une action motrice. Une autre, appelée l’hypothèse du point d’équilibre, suggère que le cortex moteur établisse et rétablisse des seuils spatiaux; les positions des segments du corps auxquelles les muscles et les réflexes commencent à s’activer. Selon ce dernier, les paramètres du mouvement sont dérivés sans pré-programmation, en fonction de la différence entre la position actuelle et la position seuil des segments du corps. Pour examiner de plus près ces deux théories, nous avons examiné l’effet d’un changement volontaire de l’angle du coude sur les influences cortico-spinales chez des sujets sains en employant la stimulation magnétique transcrânienne (TMS) par-dessus le site du cortex moteur projetant aux motoneurones des muscles du coude. L’état de cette aire du cerveau a été évalué à un angle de flexion du coude activement établi par les sujets, ainsi qu’à un angle d’extension, représentant un déplacement dans le plan horizontal de 100°. L’EMG de deux fléchisseurs du coude (le biceps et le muscle brachio-radial) et de deux extenseurs (les chefs médial et latéral du triceps) a été enregistrée. L’état d’excitabilité des motoneurones peut influer sur les amplitudes des potentiels évoqués moteurs (MEPs) élicitées par la TMS. Deux techniques ont été entreprises dans le but de réduire l’effet de cette variable. La première était une perturbation mécanique qui raccourcissait les muscles à l'étude, produisant ainsi une période de silence EMG. La TMS a été envoyée avec un retard après la perturbation qui entraînait la production du MEP pendant la période de silence. La deuxième technique avait également le but d’équilibrer l’EMG des muscles aux deux angles du coude. Des forces assistantes ont été appliquées au bras par un moteur externe afin de compenser les forces produites par les muscles lorsqu’ils étaient actifs comme agonistes d’un mouvement. Les résultats des deux séries étaient analogues. Un muscle était facilité quand il prenait le rôle d’agoniste d’un mouvement, de manière à ce que les MEPs observés dans le biceps fussent de plus grandes amplitudes quand le coude était à la position de flexion, et ceux obtenus des deux extenseurs étaient plus grands à l’angle d’extension. Les MEPs examinés dans le muscle brachio-radial n'étaient pas significativement différents aux deux emplacements de l’articulation. Ces résultats démontrent que les influences cortico-spinales et l’activité EMG peuvent être dissociées, ce qui permet de conclure que la voie cortico-spinale ne programme pas l’EMG à être générée par les muscles. Ils suggèrent aussi que le système cortico-spinal établit les seuils spatiaux d’activation des muscles lorsqu’un segment se déplace d’une position à une autre. Cette idée suggère que des déficiences dans le contrôle des seuils spatiaux soient à la base de certains troubles moteurs d’origines neurologiques tels que l’hypotonie et la spasticité. / According to a dominant theory, the motor cortex is directly involved in pre-programming motor outcome in terms of movement trajectories and electromyographic (EMG) patterns. In contrast, the equilibrium point theory suggests that the motor cortex sets and resets the spatial thresholds, i.e., the positions of body segments at which muscles and reflexes begin to act. Movement parameters thereby emerge without pre-programming, depending on the difference between the actual and the threshold position of the body segments. To choose between these two theories of motor control, we investigated corticospinal influences associated with voluntary changes in elbow joint angle in healthy individuals using transcranial magnetic stimulation (TMS) of the brain site projecting to motoneurons of the elbow muscles. In order to minimize the influence of motoneuronal excitability on the evaluation of corticospinal influences, motor evoked potentials (MEPs) elicited by TMS were obtained during the EMG silent period produced by a brief muscle shortening prior to the TMS pulse. MEPs were obtained at a flexion and an extension elbow angle actively established by subjects. MEPs were recorded from 2 elbow flexors (biceps and brachioradialis) and 2 extensors (medial and lateral heads of triceps). Flexor MEP amplitude was bigger at the elbow flexion position in the case of the biceps and extensor MEPs were bigger at the extension position in both extensors studied (reciprocal pattern). MEPs observed in the brachioradialis did not differ at the two elbow orientations. A similar difference in corticospinal influences at the two elbow positions was often preserved when the tonic activity of elbow muscles was equalized by compensating the passive muscle forces at the two positions with a torque motor. Thus, corticospinal influences and EMG activity were de-correlated and it can be concluded that the corticospinal system is not involved in pre-determining the magnitude of motor commands to muscles. Results suggest that the corticospinal system resets the spatial thresholds for muscle activation when segments move from one position to another. This implies that deficits in spatial threshold control may underlie different neurological motor problems (e.g., hypotonia and spasticity).

No description available.