Evidence of self-sustained motoneuron firing in young and older adults

Kamen, Gary; Sullivan, Ryan; Rubinstein, Scott; Christie, Anita

doi:10.1016/j.jelekin.2005.06.008

Cited by 17 publications

(18 citation statements)

References 44 publications

(51 reference statements)

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“…Surprisingly, in the standing position the soleus EMG levels of four subjects decreased after the stimulus ended, contrary to the increase described for seated subjects 9,11,[13][14][15][16]22 . One possibility for this lack of increase in soleus activity is that while standing, the plateau potential mechanism would already be activated by the action of monoaminergic modulation 23 .…”

Section: Discussioncontrasting

confidence: 87%

“…The neuron may then be turned off by, for example, a hyperpolarization caused by inhibitory synapses [9][10][11] . Strong evidence for this phenomenon has been obtained from electrical stimulation of mixed nerves and from voluntary muscle activation in human MNs 9,[11][12][13][14][15][16] . The PP phenomenon reduces the need for continuous synaptic input during muscle contraction, which may be useful in postural muscles, whose activity can be maintained without a continuous descending drive to keep the MNs firing 10,14,16 .…”

Section: Introductionmentioning

confidence: 94%

“…An electrolytic gel interface was placed between the skin and the electrode, which was then secured to the skin with micropore tape. Electrodes were attached at the following locations: the soleus (SOL) -distal to the end of the gastrocnemius muscles, the tibialis anterior (TA) -over the largest corresponding girth and at the FDB -over the plantar region of the foot, near the medial arch 16,19,20 . TA muscle activity was recorded to check for any occurrence of co-contraction or reciprocal inhibition.…”

Section: Experimental Apparatus and Data Analysismentioning

confidence: 99%

“…The feet have to be considered as a specific sensory-motor sub-system due to their importance for signaling the position of the body' s center of gravity [27][28][29] and to muscles such as the FDB, which contribute to postural control [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]30 . That increased and sustained FDB activity can be triggered by appropriate stimuli reinforces the relevance of foot muscles for postural control.…”

mentioning

confidence: 99%

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Changes in FDB and soleus muscle activity after a train of stimuli during upright stance

Okai

Kohn

2012

Rev. bras. fisioter.

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© Revista Brasileira de FisioterapiaChanges in FDB and soleus muscle activity after a train of stimuli during upright stance Alterações pós-trem de estímulo, na atividade dos músculos FDB e sóleus durante a postura ortostática Liria A. Okai 1,2 , André F. Kohn 1 AbstractBackground: Evidence of self-sustained muscle activation following a brief electrical stimulation has been reported in the literature for certain muscles. Objectives: This report shows that the foot muscle (Flexor Digitorum Brevis -FDB) shows a self-sustained increase in muscle activity during upright stance in some subjects following a train of stimuli to the tibial nerve. Methods: Healthy subjects were requested to stand upright and surface EMG electrodes were placed on the FDB, Soleus and Tibialis Anterior muscles. After background muscle activity (BGA) acquisition, a 50 Hz train of stimuli was applied to the tibial nerve at the popliteal fossa. The root mean square values (RMS) of the BGA and the post-stimulus muscle activation were computed. Results: There was a 13.8% average increase in the FDB muscle EMG amplitude with respect to BGA after the stimulation was turned off. The corresponding post-stimulus Soleus EMG activity decreased by an average of 9.2%. We hypothesize that the sustained contraction observed in the FDB following stimulus may be evidence of persistent inward currents (PIC) generated in FDB spinal motoneurons. The post-stimulus decrease in soleus activity may have occurred due to the action of inhibitory interneurons caused by the PICs, which were triggered by the stimulus train. Conclusions: These sustained post-stimulation changes in postural muscle activity, found in different levels in different subjects, may be part of a set of possible responses that contribute to overall postural control.Keywords: physical therapy; posture; foot; human; electromyography; motor activity. ResumoContextualização: Existem evidências de ativação autossustentada em certos músculos pós-estimulação elétrica. Objetivos: Mostrar que, em alguns sujeitos, o músculo do pé (Flexor Digitorum Brevis -FDB) também pode apresentar aumento de atividade autossustentada na posição ortostática pós-trem de estímulo no nervo tibial. Métodos: Sujeitos foram solicitados a permanecer na posição ortostática e sinais eletromiográficos foram coletados dos músculos FDB, sóleus e tibial anterior do membro inferior direito. Após a aquisição dos sinais eletromiográficos base (sem estimulação -BGA), um trem de estímulos de 50 Hz foi aplicado no nervo tibial (fossa poplítea).Foram analisados os valores RMS dos dados BGA e dos sinais coletados pós-estímulo. Resultados: Ao fim do estímulo, houve um aumento de 13,8% da atividade muscular do FDB em comparação com BGA. O mesmo fenômeno não aconteceu com o músculo sóleus, que apresentou uma diminuição de 9,2% da sua atividade pós-estímulo. Uma das hipóteses para a geração pós-estímulo da contração sustentada do FDB seria a da geração de corrente de entrada persistente (PIC) nos motoneurônios espinais do FDB. A diminuição da at...

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Section: Discussioncontrasting

confidence: 87%

Section: Introductionmentioning

confidence: 94%

Section: Experimental Apparatus and Data Analysismentioning

confidence: 99%

mentioning

confidence: 99%

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Changes in FDB and soleus muscle activity after a train of stimuli during upright stance

Okai

Kohn

2012

Rev. bras. fisioter.

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“…In contrast to the widely studied presence of PICs in cellular studies, the presence and function of PICs in human motor neurons have been difficult to assess. Several studies in humans have identified patterns of motor unit discharge (Kiehn & Eken, 1992, 1997; Gorassini et al , 1998; Walton et al , 2002; Kamen et al , 2006) and muscle force generation (Collins et al , 2001, 2002; Hornby et al , 2003; Baldwin et al , 2006; Blouin et al , 2009) that are consistent with behaviors attributed to PICs in cellular studies. However, the experimental techniques used in these studies are limited by their inability to detect quantitative changes in the magnitude of PICs across different motor behaviors or study populations.…”

Section: Introductionmentioning

confidence: 76%

Dependence of the paired motor unit analysis on motor unit discharge characteristics in the human tibialis anterior muscle

Stephenson

Maluf

2011

Journal of Neuroscience Methods

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The paired motor unit analysis provides in vivo estimates of the magnitude of persistent inward currents (PIC) in human motoneurons by quantifying changes in the firing rate (ΔF) of an earlier recruited (reference) motor unit at the time of recruitment and derecruitment of a later recruited (test) motor unit. This study assessed the variability of ΔF estimates, and quantified the dependence of ΔF on the discharge characteristics of the motor units selected for analysis. ΔF was calculated for 158 pairs of motor units recorded from nine healthy individuals during repeated submaximal contractions of the tibialis anterior muscle. The mean (SD) ΔF was 3.7 (2.5) pps (range −4.2 to 8.9 pps). The median absolute difference in ΔF for the same motor unit pair across trials was 1.8 pps, and the minimal detectable change in ΔF required to exceed measurement error was 4.8 pps. ΔF was positively related to the amount of discharge rate modulation in the reference motor unit (r2=0.335; P<0.001), and inversely related to the rate of increase in discharge rate (r2=0.125; P<0.001). A quadratic function provided the best fit for relations between ΔF and the time between recruitment of the reference and test motor units (r2=0.229, P<0.001), the duration of test motor unit activity (r2=0.110, P<0.001), and the recruitment threshold of the test motor unit (r2=0.237, P<0.001). Physiological and methodological contributions to the variability in ΔF estimates of PIC magnitude are discussed, and selection criteria to reduce these sources of variability are suggested for the paired motor unit analysis.

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Motor Unit

Heckman

Enoka

2012

Comprehensive Physiology

366

449

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Movement is accomplished by the controlled activation of motor unit populations. Our understanding of motor unit physiology has been derived from experimental work on the properties of single motor units and from computational studies that have integrated the experimental observations into the function of motor unit populations. The article provides brief descriptions of motor unit anatomy and muscle unit properties, with more substantial reviews of motoneuron properties, motor unit recruitment and rate modulation when humans perform voluntary contractions, and the function of an entire motor unit pool. The article emphasizes the advances in knowledge on the cellular and molecular mechanisms underlying the neuromodulation of motoneuron activity and attempts to explain the discharge characteristics of human motor units in terms of these principles. A major finding from this work has been the critical role of descending pathways from the brainstem in modulating the properties and activity of spinal motoneurons. Progress has been substantial, but significant gaps in knowledge remain.

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Evidence of self-sustained motoneuron firing in young and older adults

Cited by 17 publications

References 44 publications

Changes in FDB and soleus muscle activity after a train of stimuli during upright stance

Changes in FDB and soleus muscle activity after a train of stimuli during upright stance

Dependence of the paired motor unit analysis on motor unit discharge characteristics in the human tibialis anterior muscle

Motor Unit

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