Search

Rotation of an upper limb joint produces excitatory stretch reflex peaks M1 and M2 in the stretched muscles and simultaneous decrease in electromyographic (EMG) activity in the shortened muscles. The objective of this study was to examine whether the decreased activity in the antagonists (rINHIB) is purely from unloading of the spindles or receives active inhibition involving inhibitory interneurons. If rINHIB is due only to unloading, then the termination of rINHIB should vary with the duration of perturbation used to elicit stretch reflex, namely shorter stretches should result in shorter values of decreased periods of EMG. To examine this question, rectangular pulses, ranging in duration from 25 to 150 ms, were used to stretch wrist flexors or extensors with a torque motor. These rectangular pulses resulted in joint rotations which peaked at times ( T) ranging from approximately 75-160 ms. As shown by previous authors, when the duration of rotation was shortened, the magnitude of M1 did not change, while the magnitude of M2 decreased. However, termination time of rINHIB in the shortened muscles did not change with change in T, implying thereby that unloading of spindles of the antagonist muscles is not the only mechanism for the reduction in activity and that inhibitory reflex pathways most likely contribute. Possible sources of inhibition are discussed for the short- and long-latency inhibition. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To establish the modulation pattern of reciprocal inhibition and presynaptic inhibition of soleus Ia afferents during robot-assisted stepping in healthy subjects. Methods: During stepping, the soleus H-reflex was conditioned by percutaneous stimulation of the ipsilateral common peroneal nerve with a single pulse at stimulation intensities that ranged from 0.9 to 1.2 TA M-wave motor thresholds across subjects. To control for movement of recording and stimulating electrodes, a supramaximal stimulus 80ms after the conditioned and/or unconditioned H-reflexes was delivered to the posterior tibial nerve. The short (2, 3, 4ms) and long (60–80ms) conditioning-test intervals at which the largest amount of reflex depression was observed with the subjects seated were utilized during stepping. Stimuli were randomly dispersed across the step cycle which was divided into 16 equal bins. Results: Reciprocal inhibition exerted from flexor group I afferents onto soleus motoneurons was decreased at mid-stance and increased and late-stance and throughout the swing phase. Presynaptic inhibition of soleus Ia afferents was increased at heel strike and decreased at late-stance and early swing phases. Conclusion: Reciprocal inhibition between ankle antagonistic muscles and presynaptic inhibition of soleus Ia afferents are modulated in a similar pattern to that reported during walking on a treadmill with full weight bearing and without robot-assisted leg movement. Significance: The activity of spinal interneuronal circuits engaged in patterned locomotor activity supports a reciprocal gait pattern during robot-assisted stepping in healthy humans. [Copyright &y& Elsevier]

Abstract: Interlimb neural linkages relay activity related to rhythmic arm movement to the lumbar spinal cord. This is detected by modulated reflex amplitudes in muscles remote from the rhythmic movement. Improved understanding of modulation in ankle flexor and extensor muscles due to rhythmic arm movement can be gained using modulation of spinal excitability as a probe. The modulatory effect of rhythmic arm movement on Ia reciprocal inhibition (RI) between functional antagonists at the ankle has not been studied. We investigated the influence of rhythmic arm cycling on short latency (∼55ms post-stimulus) RI between ankle flexor (tibialis anterior, TA) and extensor (soleus, SOL) muscles at varying (0.9, 1.0, 1.2, 1.5 and 2.0× motor threshold (MT)) stimulus intensities. We hypothesized that arm cycling would increase RI between antagonists, but that movement conditioning would vary depending on stimulus intensity used to evoke the RI response. Amplitude of RI deduced from suppression of ongoing EMG activity was compared in static and arm cycling conditions. Arm cycling significantly (p <0.05) increased RI in SOL at 1.0×MT, but had no effect in TA at any stimulus intensity (p >0.05). Descending signals arising from rhythmic arm movement significantly alter transmission in RI pathways between ankle flexor and extensor muscles differentially. This may be due to differences in descending supraspinal inputs to ankle flexors vs. extensors, and could be related to functional requirements during locomotion. [Copyright &y& Elsevier]

The purpose of this study was to determine to what extent one session of isotonic and isometric ankle dorsi and plantar flexion training induces changes in the frequency-dependent depression of the soleus H-reflex. Further, adaptation of reciprocal Ia inhibition exerted from tibialis anterior flexor group I afferents on soleus motoneurons, and presynaptic inhibition of Ia afferent terminals induced by a conditioning afferent volley following stimulation of the antagonist nerve were established with subjects seated before and after training. The soleus H-reflexes evoked at the inter-stimulus intervals of 1, 2, 3, 5, and 8 s were normalized to the mean amplitude of the H-reflex evoked every 10 s. Conditioned H-reflexes were normalized to the associated control H-reflex evoked with subjects seated before and after training. Twenty-six subjects were randomly assigned to one or more of the 4 exercise groups. Isometric ankle dorsi flexion training decreased the reciprocal and presynaptic inhibition, while isotonic ankle dorsi flexion had no significant effects. Isotonic plantar flexion training decreased only the reciprocal inhibition, whilst isometric plantar flexion had no significant effects on the reciprocal or presynaptic inhibition. None of the training exercise protocols affected the amount of homosynaptic depression of the soleus H-reflex. Our findings support the notion that plastic changes of reciprocal and presynaptic inhibition due to exercise are transferrable to a resting state, and that homosynaptic depression remains unaltered after a single session of ankle training. Further research is needed to outline the time-course of plastic changes of spinal inhibitory mechanisms in humans. [ABSTRACT FROM AUTHOR]

Purpose: Learning a skilled movement is associated with more efficient use of subcortical motor circuits which can coordinate features of the movements such as the timing and patterns of activation of different muscles. Learning a motor skill could strengthen spinal interneuron circuits that facilitate the movement. We hypothesized that learning a simple, alternating movement would produce changes in spinal circuits that mediate reciprocal inhibition between antagonist muscles. Methods: Sixteen healthy adult subjects were trained to perform a wrist flexion and extension task to control the movement of a cursor between targets appearing on a computer display. The goal of the task was to hit the targets. Subjects practiced for 15 minutes daily until reaching the acquisition criterion. Surface EMG recordings from wrist flexor and extensor muscles showed reduced co-contraction during acquisition of the task. Results: Compared to the initial session, in the final session short-latency reciprocal inhibition was enhanced during the late-extension phase in the final session. This phase-dependent increase in short-latency reciprocal inhibition is likely to facilitate switching activation between wrist antagonistic muscles. Conclusions: Learning a motor skill can produce alterations in spinal reflex circuits that facilitate the desired movement. [ABSTRACT FROM AUTHOR]

Abstract: Reciprocal inhibition of antagonist muscles is crucial for motor skill learning in humans. However, the changes in reciprocal inhibition function during the motor learning process are unknown. The aim of this study was to systematically observe the changes in reciprocal inhibition function. We investigated the optimal coil position for simultaneously eliciting motor evoked potentials (MEPs) of reciprocal muscles, and the reciprocal changes in input–output (IO) curves during motor skill training. From ten healthy volunteers, the IO curves of MEPs were measured for the midpoint between the center of gravity (CoG) of the extensor carpi radialis (ECR) and the flexor carpi radialis (FCR) muscles, for the CoG of ECR, and for the FCR muscles using transcranial magnetic stimulation (TMS). In addition, the IO curves of the ECR and the FCR muscles were measured before and after the motor skill training of rapid wrist extension. The IO curves measured at the midpoint between the CoGs of the ECR and the FCR muscles and the CoG of each muscle were homogenous. However, after training to perform rapid wrist extension, the IO curve of the agonist (ECR) muscle was increased, while the antagonist (FCR) muscle was decreased. The present findings validate the IO curves simultaneously measured for reciprocal muscles, and suggest that motor skill training could induce reciprocal change in corticospinal excitability. [Copyright &y& Elsevier]

Abstract: Two studies using an ABA design examined the Extinction and renewal of conditioned barpress suppression. Following lights-off and foot shock pairings in Context A, rats were placed in Context B and were given either a standard counterconditioning procedure where the lights-off CS was paired with a novel food US delivered freely or a modified counterconditioning procedure where CS-US pairings only occurred if the rat earned the US by performing a required behavior during the CS. Results indicated that the modified counterconditioning procedure thwarted ABA renewal but the conventional counterconditioning procedure did not reduce ABA renewal any more than nonreinforced exposure to the CS alone. Furthermore, the response required during the modified counterconditioning procedure could be one used as a baseline response during Acquisition of fear or it could be a novel response. Implications of the results for theories of Extinction and renewal of fear are discussed. [Copyright &y& Elsevier]

Abstract: The aim of this study was to evaluate motor unit activity from a latent myofascial trigger point (MTP) in an antagonist muscle during isometric agonist muscle contraction. Intramuscular activity was recorded with an intramuscular electromyographic (EMG) needle inserted into a latent MTP or a non-MTP in the posterior deltoid muscle at rest and during isometric shoulder flexion performed at 25% of maximum voluntary contraction in 14 healthy subjects. Surface EMGs were recorded from the anterior and posterior deltoid muscles. Maximal pain intensity and referred pain induced by EMG needle insertion were recorded on a visual analogue scale. The results showed that higher local pain was observed following needle insertion into latent MTPs (4.64 ± .48 cm) than non-MTPs (2.35 ± .43 cm, P < .005). Referred pain was reported in 6/14 subjects following needle insertion into latent MTPs, but none into the non-MTPs. The intramuscular EMG activity, but not surface EMG activity, in the antagonist muscle was significantly higher at rest and during shoulder flexion at latent MTPs than non-MTPs (P < .05). The current study provides the first evidence that increased motor unit excitability is associated with reduced antagonist reciprocal inhibition. Perspective: This study shows that MTPs are associated with reduced efficiency of reciprocal linhibition, which may contribute to the delayed and incomplete muscle relaxation following exercise, disordered fine movement control, and unbalanced muscle activation. Elimination of latent MTPs and/or prevention of latent MTPs from becoming active may improve motor functions. [Copyright &y& Elsevier]

Copyright of Kinesiologia Slovenica is the property of Faculty of Sport and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Sniffing out of sight always the same colorless and odorless solution containing no thermal agents while viewing a bottle with colored water increases sensitivity of the left nostril/right hemisphere (RH) for warming sensations and sensitivity of the right nostril/left hemisphere (LH) for cooling sensations. It is likely that engagement in a temperature judgment task and the development of specific expectancies due to the presence of color cues alter and enhance processing in brain areas involved in thermosensory processing. The lateralized patterns thus intimate hemispheric specialization for thermosensory processing probably originating in reciprocal inhibition that confers balance between the hemispheres. If the inhibition-balance hypothesis were correct then the more the left nostril proves sensitive to warming the more the right nostril would prove sensitive to cooling. One hundred and ninety one healthy volunteers were tested here. The left nostril dominance for warming and the right dominance for cooling were replicated once more. The dominance of the left nostril for warming (left minus right nostril) correlated highly with the dominance of the left nostril to cooling (right minus left nostril) and the individual patterns of results were distributed along an axis starting from the expected left nostril/warming – right nostril/cooling pattern and ending at the opposite left nostril/cooling – right nostril/warming pattern. Furthermore, the point where the left nostril dominance for warming responses dropped and inverted perfectly coincided with the point where the right nostril dominance for cooling responses inverted too. Such a good continuum between the expected and the opposite patterns supports the inhibition-balance hypothesis. Finally, 66% of subjects exhibited the expected left-warming/right-cooling pattern suggesting, therefore, that, despite this continuum, there is a dominant lateral specialization for temperature processing. [Copyright &y& Elsevier]

Abstract: The aim of this study was to establish the modulation pattern of the reciprocal inhibition exerted from tibialis anterior (TA) group I afferents onto soleus motoneurons during body weight support (BWS) assisted stepping in people with spinal cord injury (SCI). During assisted stepping, the soleus H-reflex was conditioned by percutaneous stimulation of the ipsilateral common peroneal nerve at one fold TA M-wave motor threshold with a single pulse delivered at a short conditioning-test interval. To counteract movement of recording and stimulating electrodes, a supramaximal stimulus at 80–100ms after the test H-reflex was delivered. Stimuli were randomly dispersed across the step cycle which was divided into 16 equal bins. The conditioned soleus H-reflex was significantly facilitated throughout the stance phase, while during swing no significant changes on the conditioned H-reflex were observed when compared to the unconditioned soleus H-reflex recorded during stepping. Spontaneous clonic activity in triceps surae muscle occurred in multiple phases of the step cycle at a mean frequency of 7Hz for steps with and without stimulation. This suggests that electrical excitation of TA and soleus group Ia afferents did not contribute to manifestation of ankle clonus. Absent reciprocal inhibition is likely responsible for lack of soleus H-reflex depression in swing phase observed in these patients. The pronounced reduced reciprocal inhibition in stance phase may contribute to impaired levels of co-contraction of antagonistic ankle muscles. Based on these findings, we suggest that rehabilitation should selectively target to transform reciprocal facilitation to inhibition through computer controlled reflex conditioning protocols. [Copyright &y& Elsevier]

Abstract: Objective: Patterned sensory electrical stimulation (PES) has been shown to induce plasticity in spinal reciprocal Ia inhibition of the calf muscles. To study the cortical modulation of spinal plasticity, we examined the effects of giving transcranial direct current stimulation (tDCS) to the motor cortex before PES. Methods: Seven healthy volunteers participated in this study. PES involved stimulating the left common peroneal nerve at the fibular head with a train of 10 pulses at 100Hz every 1.5s for 20min using an intensity equal to the motor threshold of the tibialis anterior. tDCS was applied for 10min before PES. For anodal stimulation, the electrode was placed over the motor cortex, and the cathodal electrode over the contralateral supraorbital area. For cathodal stimulation, the electrodes were reversed. Reciprocal inhibition was assessed using a soleus H reflex conditioning-test paradigm. Results: PES increased disynaptic reciprocal inhibition from the peroneal nerve to the soleus H reflex. When cathodal tDCS was applied before PES, PES no longer increased reciprocal inhibition. Conclusions: Applying tDCS before PES modulated the effects of PES on spinal reciprocal inhibition in a polarity specific manner. Significance: We suggest that the motor cortex may play a role in spinal plasticity. [Copyright &y& Elsevier]

Abstract: Reciprocal inhibition (RI) between different muscles has been used as an explanation for the effect of some treatments. Consequently, there may be a presumption that RI is bi-directional and equal between every agonist antagonist muscle pair. That is, the strength of RI from agonist to antagonist is equal to that from antagonist to agonist. With this in mind we investigated RI between quadriceps and hamstrings using 2 techniques to explore if a) it is evoked between this agonist antagonist pair and b) if it is equal and opposite in strength. Firstly, electromygraphic (EMG) activity of one muscle was recorded whilst stimulating group Ia afferents from the other. The second approach involved conditioning a reflex evoked in one muscle by stimulating Ia afferents from the other. Using the first approach, short-latency inhibition thought to be RI, was observed more frequently (p <0.000) and was larger (p <0.05) from femoral nerve stimulation to hamstrings than the inhibition evoked in quadriceps by sciatic nerve stimulation. The second approach revealed a similar pattern. RI between quadriceps and hamstrings is not actually reciprocal i.e. not equal in both directions. Our presumptions about the frequency and strength of other pathways between different agonist antagonist pairs need to be assessed. [Copyright &y& Elsevier]

In a variety of vertebrates, including turtle, many classical and contemporary studies of spinal cord neuronal networks generating rhythmic motor behaviors emphasize a Reciprocal Model with alternation of agonists and antagonists, alternation of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs), and reciprocal inhibition. Some studies of spinal cord neuronal networks, including some in turtle during scratch motor rhythms, describe a Balanced Model with concurrent EPSPs and IPSPs. The present report reviews turtle spinal cord studies and concludes that there is support for a Combined Model with both alternating and concurrent excitation and inhibition, that is, characteristics of both the Reciprocal and the Balanced Models, in the same spinal cord neuronal network for scratch reflex in turtle. Studies of spinal cord neuronal networks for locomotion in a variety of vertebrates also support a Combined Model. [ABSTRACT FROM AUTHOR]

Purpose: NiCl2 (15 µM) enhances the ERG b-wave amplitude of vertebrate retina, up to 1.5-fold by blocking E/R-type voltage-gated Ca2+ channels, which is mediated by blocking the release of GABA onto ionotropic GABA-A and GABA-C receptors. In vivo, it is likely that zinc, rather than nickel ions, may be involved in the modulation of retinal signalling. Therefore, we tested the effect of both, ZnCl2 (10 to 500 µM) and DEDTC (100 to 500 µM), which chelates zinc ions for the capacity to influence the ERG b-wave amplitude. Methods: Transretinal potentials from the isolated bovine retina were recorded as electroretinograms and Ca2+ inward currents by patch-clamp recordings of stably Cav2.3 transfected HEK-293 cells, yielding an IC50 value of 5.3 µM for ZnCl2. Results: ZnCl2 (10–15 µM) increased the b-wave amplitude by 1.52-fold ± 0.12 ( n = 6 retinas), which was partially reversible upon washout. The same 1.5-fold stimulation of the b-wave amplitude was reported recently for 15 µM NiCl2. The superfusion of isolated retinas by DEDTC (100 µM) caused a transient decrease of the ERG b-wave amplitude (0.75-fold ± 0.06; n = 4), suggesting that the co-secretion of Zn2+ ions may occur under scotopic conditions. Conclusion: The stimulatory effect of ZnCl2 on the ERG b-wave amplitude resembles the stimulatory effect of NiCl2 and may be mediated rather by the NiCl2-sensitive, Cav2.3 E-/R-type voltage-gated Ca2+ channels than by NiCl2-sensitive T-type channels. [ABSTRACT FROM AUTHOR]

Callosal disconnection signs are closely related to asymmetric hemispheric specialization of cognitive functions. Although extinction is more commonly associated with the right parietotemporal lesion, it may occur following lesions of the corpus callosum. After an infarction involving the left splenium, a 58-year-old right-handed man had no disconnection symptoms that had been reported earlier, but showed visual extinction with left or right visual hemifield dominant stimuli. Our results suggest that dominance specific visual extinction might be another disconnection sign associated with splenial lesion. [ABSTRACT FROM AUTHOR]

Purpose: NiCl2 (15 μM) stimulates the electroretinogram (ERG) b-wave amplitude of vertebrate retina up to 1.5-fold through its blocking of E/R-type voltage-gated Ca2+ channels. Assuming that such an increase is mediated by blocking the release of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) via ionotropic GABA receptors, we tested the effect of both GABA itself and GABA-receptor antagonists such as (−)bicuculline (1.51-fold increase) and (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA; 1.46-fold increase) on the b-wave amplitude. Methods: Recording of the transretinal potentials from the isolated bovine retina. Results: GABA (100 μM) reduced the b-wave amplitude only when NiCl2 (15 μM) was applied first. Each antagonist applied on its own stimulated the b-wave amplitude only partially: subsequent NiCl2 superfusion caused a small but additional increase, leading to a 1.69- and a 1.88-fold total increase of the amplitude by Ni2+ plus (−)bicuculline or Ni2+ plus TPMPA, respectively. Only the application of both antagonists in combination, before superfusing low NiCl2 (15 μM), completely prevented subsequent stimulation by NiCl2 with a similar 1.90-fold total increase of b-wave amplitude. Those retina segments that did not respond to NiCl2 could not be stimulated by (−)bicuculline and vice versa. Conclusion: The stimulatory effect of NiCl2 on the ERG b-wave amplitude is mainly, but not only, mediated by a NiCl2-sensitive, Cav2.3-triggered GABA release acting through ionotropic GABA-A and GABA-C receptors. [ABSTRACT FROM AUTHOR]

Abstract: Old adults execute single-joint voluntary movements with heightened antagonist muscle coactivation and altered timing between agonist and antagonist muscles. It is less clear if old adults adopt similar strategies during the most common form of activity of daily living, gait, and if age and gait velocity interact. We compared antagonist muscle activation amplitude and onset, offset, and activation duration of the vastus lateralis, biceps femoris, tibialis anterior, and gastrocnemius lateralis from surface EMG in 17 young (age 19–25) and 17 old adults (age 71–85) while walking at 1.2, 1.5, and 1.8m/s. All participants were healthy and highly mobile. The activation level of the four muscles when each acted as the antagonist was, on the average, 83% higher in old vs young adults (for each muscle p <0.05). In two of four muscles this activation increased with gait velocity in young but not in old adults. The inter-burst interval between TA and GL was two-fold (83ms) longer in young vs old adults and at higher gait velocities it became 14% (24ms) shorter in young but 51% (31ms) longer in old adults (interaction, p =0.015). It is concluded that there is an interaction between age and gait velocity in the amplitude and timing of antagonist muscle coactivation. [Copyright &y& Elsevier]

Abstract: Objective: To understand the effect of continuous theta burst stimulation (cTBS) given to the premotor area, we studied the circuits within the primary motor cortex and spinal cord after cTBS over the dorsal premotor area (PMd). Methods: Three sets of parameters, including corticospinal excitability, short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) and forearm reciprocal inhibition (RI) were tested. Results: Paralleling the effects of cTBS applied directly to the primary motor cortex, cTBS over the left PMd suppressed corticospinal excitability as measured by the change in the size of MEPs evoked by single pulse TMS over primary motor cortex. Premotor cTBS appeared to have a longer lasting, but no more powerful effect on corticospinal excitability than motor cTBS, however, unlike motor cTBS it had no effect on SICI or ICF. Finally, although premotor cTBS had no effect on spinal H-reflexes, it did reduce the third phase of RI between forearm extensor and flexor muscles. Conclusions: Premotor cTBS is a quick and useful way of modulating excitability in cortical and possibly subcortical motor circuits. Significance: Premotor cTBS can be used as an alternative to regular rTMS to evaluate cortical function, motor behaviours and the response to disease therapy. [Copyright &y& Elsevier]

Background and objective. We devised a therapeutic approach to facilitate the use of the hemiparetic upper extremity (UE) in daily life by combining integrated volitional control electrical stimulation with a wrist splint, called hybrid assistive neuromuscular dynamic stimulation (HANDS). Methods. Twenty patients with chronic hemiparetic stroke (median 17.5 months) had moderate to severe UE weakness. Before and immediately after completing 3 weeks of training in 40-minute sessions, 5 days per week over 3 weeks and wearing the system for 8 hours each day, clinical measures of motor impairment, spasticity, and UE functional scores, as well as neurophysiological measures including electromyography activity, reciprocal inhibition, and intracortical inhibition were assessed. A follow-up clinical assessment was performed 3 months later. Results. UE motor function, spasticity, and functional scores improved after the intervention. Neurophysiologically, the intervention induced restoration of presynaptic and long loop inhibitory connections as well as disynaptic reciprocal inhibition. Paired pulse transcranial magnetic stimulation study indicated disinhibition of the short intracortical inhibition in the affected hemisphere. The follow-up assessment showed that improved UE functions were maintained at 3 months. Conclusion. The combination of hand splint and volitional and electrically induced muscle contraction can induce corticospinal plasticity and may offer a promising option for the management of the paretic UE in patients with stroke. A larger sample size with randomized controls is needed to demonstrate effectiveness. [ABSTRACT FROM AUTHOR]

Objective. Spinal reciprocal inhibitory and excitatory reflexes of ankle extensor and flexor muscles were investigated in ambulatory participants with chronic central nervous system (CNS) lesions causing foot drop as a function of time after lesion and stimulator use. Methods. Thirty-nine participants with progressive (eg, secondary progressive MS) and 36 with generally nonprogressive (eg, stroke) conditions were studied. The tibialis anterior (TA) and soleus maximum H-reflex/M-wave (H[submax]/M[submax]) ratios and maximum voluntary contractions (MVC) were measured and compared with those in age-matched control participants. Reciprocal inhibition was measured as a depression of the ongoing electromyographic (EMG) activity produced by antagonist muscle-nerve stimulation. Results. Participants with CNS lesions had significantly higher soleus H[submax]/M[submax] ratios than control participants, and reduced voluntary modulation of the reflexes occurred in both muscles. Reciprocal inhibition of soleus from common peroneal (CP) nerve stimulation was not significantly different from controls in either group. Inhibition of the TA by tibial nerve stimulation decreased and was eventually replaced by excitation in participants with nonprogressive disorders. No significant change occurred in progressive disorders. Use of a foot drop stimulator increased the TA, but not the soleus MVC overall. H-reflexes only showed small changes. Reciprocal inhibition of the TA increased considerably, while that of the soleus muscle decreased toward control values. Conclusions. Disorders that produce foot drop also produce reflex changes, some of which only develop over a period of years or even decades. Regular use of a foot drop stimulator strengthens voluntary pathways and changes some reflexes toward control values. Thus, stimulators may provide multiple benefits to people with foot drop. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To examine neurophysiological evidence of functional involvement of the brainstem and spinal cord and motor cortical excitability in sialidosis type I, a rare inherited neurodegenerative disorder caused by mutations in the NEU1 gene. Methods: We investigated particular pathways in the brainstem, spinal cord and motor cortex in 12 genetically proven cases of sialidosis type I by assessing blink reflex recovery cycle (BR), spinal reciprocal inhibition (RI), input–output curves (I/O), short interval intracortical inhibition (SICI), intracortical facilitation (ICF) and silent period (SP). Results: The BR and RI were normal. The slope of I/O was significantly increased, and SICI and the duration of SP were reduced in sialidosis patients. Conclusions: Despite reports of pathology involving brainstem and anterior horn neurones, there were no obvious abnormalities in spinal and brainstem reflexes in the present patients, suggesting that the major clinical effects may be caused by changes at a level above the brainstem. Significance: For the first time, the integrity of certain brainstem and spinal cord reflexes in addition to motor cortical facilitatory and inhibitory circuits has been assessed in genetically proven type I sialidosis. This provides new data to aid in understanding of the pathophysiology of motor system dysfunction in this condition. [Copyright &y& Elsevier]

It is suggested that co-contraction of antagonist motor units perhaps due to abnormal disynaptic Ia reciprocal inhibition is responsible for Parkinsonian rigidity. A neural model of Parkinson's disease bradykinesia is extended to incorporate the effects of spindle feedback on key cortical cells and examine the effects of dopamine depletion on spinal activities. Simulation results show that although reciprocal inhibition is reduced in DA depleted case, it doesn't lead to co-contraction of antagonist motor neurons. Implications to Parkinsonian rigidity are discussed. [ABSTRACT FROM AUTHOR]

If reduced reciprocal inhibition plays a causal role in the pathophysiology of spasticity as has been suggested in several studies, the inhibition is expected to be impaired in spastic, but not in normal muscles. Patients with neurolathyrism offer a possibility of testing this prediction since the spastic symptoms in these patients are restricted to the lower extremities only. Three patients with neurolathyrism were tested. Their data were compared with 15 age-matched healthy subjects. All patients showed signs of spasticity in the legs. Two patients had normal voluntary muscle force in the lower extremities and one had decreased force. No clinical abnormalities were found in the upper extremities. Reciprocal inhibition between ankle dorsiflexor and plantarflexor muscles was absent in all patients, whereas the inhibition between wrist extensor and flexor muscles was present and of normal size and latency. These findings are consistent with the hypothesis that reduced reciprocal inhibition plays a causal role in the pathophysiology of spasticity. [ABSTRACT FROM AUTHOR]

The author presents a model for teaching graduate students about trauma treatment based on the principles of resourcing, titration, and reciprocal inhibition. The author reviews relevant literature on the issue of teaching trauma and recommendations for faculty, followed by examples of how to use the above principles in a 6-week university-based graduate course on trauma counseling. Evidence supporting the use of the author’s teaching model is anecdotal, and as such, the author identifies future research that will inform counseling psychology educators as this field continues to develop. [ABSTRACT FROM PUBLISHER]

Background: Immunoglobulin (Ig) E-double positivity for honeybee (HB) and yellow jacket (YJ) venom causes diagnostic difficulties concerning therapeutical strategies. The aim of this study was to clarify the cause and relation of the cross-reactivity in patients with insect venom allergy. Methods: For this purpose, 147 patients with suspected stinging insect allergy and CAP-FEIA-double positivity were investigated for specific sIgE to additional cross-reactive carbohydrate determinant (CCD)-containing allergens: timothy grass pollen, rape pollen, natural rubber latex (NRL), bromelain, and horseradish peroxidase (HRP). Sera with sIgE to NRL were further investigated with the commercially available recombinant latex allergens. Reciprocal inhibition assays with both venoms and HRP were performed. Results: About 36 of 147 (24.5%) patients had sIgE to both venoms only. However, 111 of 147 (75.5%) additionally reacted to CCD-carrying allergens. 89 of 111 CCD-reactive sera had NRL-sIgE. In cases where inhibition experiments were performed, the NRL-sIgE binding was completely abolished in the presence of HRP. Only nine of 61 sera were positive for at least one recombinant latex allergen; all of them were negative in history and NRL-skin prick test. In 43 sera containing sIgE to CCD, HRP inhibition revealed unequivocal results: In 28 of 43 (65%) an HRP-inhibition >70% of sIgE to one venom occurred, pointing out the relevant venom. In three of 43 sIgE proved to be entirely CCD-specific. Conclusions: Our data indicate that in cases of IgE positivity to both insect venoms supplementary screening tests with at least one CCD-containing allergen should be performed; HRP being a suitable tool for this test. In addition, subsequent reciprocal inhibition is an essential diagnostic method to specify cross-reacting sIgE results. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate short-term effects of walking with functional electrical stimulation (FES) on inhibitory and excitatory spinal reflexes in healthy subjects. The FES was applied to the common peroneal (CP) nerve during the swing phase of the step cycle when the ankle flexors are active. We have previously shown that corticospinal excitability for the tibialis anterior (TA) muscle increased after 30 min of FES-assisted walking. An increase of corticospinal excitability could be due to the changes in spinal and/or cortical excitability. Thus, we wished to examine whether a short-term application of FES would increase spinal motoneuronal excitability. Changes could also result from effects on inhibitory as well as excitatory pathways, but to our knowledge no studies have investigated short-term effects of FES on spinal inhibitory pathways. Therefore, we measured reciprocal and presynaptic inhibition, as well as reflex excitability, before and after FES-assisted walking. As controls, effects of FES-like stimulation at rest and walking without stimulation were tested in separate sessions. The TA H-reflex amplitude did not increase after FES in any of the conditions tested, so we have no evidence that FES increases spinal excitability for the TA. The soleus H-reflex decreased slightly (10%) after FES-assisted walking, and remained decreased for at least 30 min. However, the control experiment indicated that this decrease was associated with walking and not with stimulation. Thirty minutes of FES did not produce any significant effects on spinal inhibitory pathways examined in the present study. In conclusion, the soleus H-reflex showed a small but consistent decrease and no spinal circuits examined showed an increase, as was observed in the corticospinal excitability. Thus, we suggest that a short-term application of FES increases the excitability of the cortex or its connections to the spinal cord more effectively than that of spinal pathways. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) of the motor cortex are facilitated by voluntary muscle contraction. We evaluated the effects of imagination of movements on MEP latencies of agonist and antagonist muscles in the hand using TMS. Twenty-two healthy volunteers were studied. TMS delivered at rest and while imagining tonic abduction of the right thumb. MEPs were recorded in response to magnetic stimulation over the scalp and cervical spine (C7–T1), and central motor conduction times (CMCT) were calculated. MEPs were recorded from right abductor pollicis brevis muscle (APB) and adductor pollicis muscle (AP) simultaneously. Imagination of abduction resulted in a shortened latency of MEPs in the APB muscle, and a prolonged latency in the AP muscle. But the imagination caused no significant change in the latency of MEPs elicited by stimulation over the cervical spine. The changes of the CMCT may account for these latency changes with imagination of movement. These findings indicate that imagination of thumb abduction facilitates motoneurons of agonist muscle and has an inhibitory effect on those of antagonist muscle (reciprocal inhibition). [Copyright &y& Elsevier]

The present studies are designed to further characterise the interneuronal pathway mediating the disynaptic reciprocal group I inhibition between flexors and extensors at the wrist and the elbow levels in humans. In the first series of experiments, we compared the electrical threshold of the reciprocal group I inhibition at the wrist and the elbow level after a prolonged vibration aimed at raising the electrical threshold of the antagonistic activated Ia afferents. Prolonged vibration to the ‘conditioning’ tendon, which raised significantly the electrical threshold of the inhibition at the elbow level, did not alter it at the wrist level. These results suggest that the dominant input to the relevant interneurones is Ia in origin at the elbow level but Ib in origin at the wrist level. In the second series of experiments, using the spatial facilitation method, we compared the effects on the post-stimulus time histograms of single voluntarily activated motor units of two volleys delivered both separately and together to group I afferents in the nerves supplying the homonymous and antagonistic muscles. At the wrist, but not at the elbow level, the peak of homonymous monosynaptic group I excitation was reduced on combined stimulation, although the antagonistic IPSP was just at the threshold. Because the suppression did not involve the initial bins of the peak, it is argued that the suppression is not due to presynaptic inhibition of Ia terminals, but probably reflects convergence between the homonymous and antagonistic volleys onto the interneurones mediating the disynaptic inhibition. Taken together with the previously reported effects of recurrent inhibition on reciprocal inhibition, these results suggest that inhibition between flexors and extensors is differently organised at the elbow (reciprocal Ia inhibition) and the wrist (non-reciprocal group I inhibition) levels. It is argued that the particular connectivity at the wrist level might correspond to some functional requirements at this ball joint. [ABSTRACT FROM AUTHOR]

The article discusses the evidence for spinal circuits interceding the change in motor behavior and muscle coactivation associated with age. It is said that age changes the control of voluntary movement of an individual. An oftentimes observed adaptation is the increased agonist and antagonist muscle coactivation. Disynaptic reciprocal inhibition is the main spinal coordinator of the agonist-antagonist muscle processes.

We examined two issues for the Eriksen task with two types of stimuli, the central target letter of which was flanked with noise (e.g., HHHHH for compatible stimuli and SSHSS for incompatible stimuli). First, we examined whether or not a response-stop function is carried out until the check operation to detect and correct erroneous response readiness has finished ( Eriksen & Eriksen, 1974 ). Second, reaction times for incompatible stimuli are not prolonged if only identical noise stimuli are used throughout the block. This phenomenon is called the blocking effect. We then explored whether or not the blocking effect can be caused by the selective inhibition of erroneous response readiness ( Eriksen & Schultz, 1979 ). Sixteen participants (18–29 years old) selectively pressed one of two buttons for the target letter. The results showed that the negative potential related to the response-stop function was enlarged for incompatible stimuli. Moreover, the blocking effect was observed, while erroneous response readiness was still observable for incompatible stimuli. These results suggest that the blocking effect is caused by something other than reciprocal inhibition. [ABSTRACT FROM AUTHOR]

Repetitive transcranial magnetic stimulation (rTMS) has been shown to induce adaptations in cortical neuronal circuitries. In the present study we investigated whether rTMS, through its effect on corticospinal pathways, also produces adaptations at the spinal level, and what the neuronal mechanisms involved in such changes are. rTMS (15 trains of 20 pulses at 5 Hz) was applied over the leg motor cortical area in ten healthy human subjects. At rest motor evoked potentials (MEPs) in the soleus and tibialis anterior muscles were facilitated by rTMS (at 1.2×MEP threshold). In contrast, the soleus H-reflex was depressed for 1 s at stimulus intensities from 0.92 to 1.2×MEP threshold. rTMS increased the size of the long-latency depression of the soleus H-reflex evoked by common peroneal nerve stimulation and decreased the femoral nerve facilitation of the soleus H-reflex. These observations suggest that the depression of the H-reflex by rTMS can be explained, at least partly, by an increased presynaptic inhibition of soleus Ia afferents. In contrast, rTMS had no effect on disynaptic reciprocal Ia inhibition from ankle dorsiflexors to plantarflexors. We conclude that a train of rTMS may modulate transmission in specific spinal circuitries through changes in corticospinal drive. This may be of relevance for future therapeutic strategies in patients with spasticity. [ABSTRACT FROM AUTHOR]

The efficient coordination of agonist and antagonist muscles is one of the important early adaptations in resistance training responsible for large increases in strength. Weak antagonist muscles may limit speed of movement; consequently, strengthening them leads to an increase in agonist muscle movement speed. However, the effect of combining agonist and antagonist muscle exercises into a power training session has been largely unexplored. The purpose of this study was to determine if a training complex consisting of contrasting agonist and antagonist muscle exercises would result in an acute increase in power output in the agonist power exercise. Twenty-four college-aged rugby league players who were experienced in combined strength and power training served as subjects for this study. They were equally assigned to an experimental (Antag) or control (Con) group and were no different in age, height, body mass, strength, or maximal power. Power output was assessed during bench press throws with a 40-kg resistance (BT P40) with the Plyometric Power System training device. After warming up, the Con group performed the BT P40 tests 3 minutes apart to determine if any acute augmentation to power output could occur without intervention. The Antag group also performed the BT P40 tests; however, an intervention strategy of a set of bench pulls, which is an antagonistic action to the bench throw, was performed between tests to determine if this would acutely affect power output during the second BT P40 test. Although the power output for the Con group remained unaltered between test occasions, the significant 4.7% increase for the Antag group indicates that a strategy of alternating agonist and antagonist muscle exercises may acutely increase power output during complex power training. This result may affect power training and specific warm-up strategies used in ballistic sports activities, with increased emphasis placed upon the antagonist muscle groups. [ABSTRACT FROM AUTHOR]

Abstract: Objective. To compare patterns of muscle activation in the lower extremity and subsequent forces during sit to stand in persons with Parkinsonism. Background. There is an interruption of the tibialis anterior/soleus interaction during forward oriented movements in some subjects with Parkinsonism, including sit to stand. This task is a major determinant of independence and 44% of those with Parkinsonism report difficulty. Methods. 41 subjects with Parkinsonism were asked to stand up from a bench. Peak acceleration and vertical ground reaction forces, the slopes to these peaks, and the timing of events were measured. Surface electrodes were placed on tibialis anterior and soleus. Results. The slower group produced force at slower rate than the fast group. The slower group spent 64% of the time taken to stand to complete the flexion-momentum phase, and the fast group spent 56%. The slower group had a larger proportion of co-contraction trials than the other groups. Conclusions. Slower subjects took longer to perform the task due to a longer time for seat off. Deficits recruiting tibialis anterior may contribute to the decreased rate of production of the acceleration forces and the longer time required for seat off. Relevance Decreased rate of rise of force is used to identify fallers in the elderly and subjects with stroke. Decreased rates of force production may therefore assist in identifying those with Parkinsonism at risk of falls. Treatment strategies designed to facilitate tibialis anterior activation may improve the functional performance of this task. [Copyright &y& Elsevier]

STUDY DESIGN::Electromyographic study in complete and incomplete spinal cord injury (SCI). OBJECTIVE::To examine the changes in the pattern of reciprocal inhibition between agonist and antagonist muscles in SCI. SETTINGS::Sensory Motor Performance Program, Rehabilitation Institute of Chicago, IL, USA. METHODS::Tendon taps were delivered manually with an instrumented hammer to the tendons of the tibialis anterior and soleus muscle in positions of full-ankle dorsiflexion and plantarflexion in eight subjects with complete SCI and eight subjects with incomplete SCI. Electromyographic activity (EMG) was recorded from ankle dorsiflexor and plantarflexor muscles. Tapping force was also recorded by a force sensor mounted to the tendon hammer, indicating the stimulus onset. Measures of reflex EMG magnitude and reflex latency were obtained for both agonist and antagonist muscles. The ratio of antagonist to agonist EMG was computed based on normalized EMG. RESULTS::Substantial reflex responses occurred in both the stretched muscle and in its antagonist. The reflex in antagonist, which we term‘reciprocal facilitation (RF)’, was most evident in subjects with incomplete SCI. The magnitude of RF was consistently greater than reflex responses in agonist muscles under all test conditions. The latency of the RF was comparable to that of monosynaptic reflex response. CONCLUSIONS::Following SCI, reciprocal organization of segmental reflexes at the ankle is often partially or completely suppressed, allowing reflex activation in antagonist muscles to be manifested. Possible mechanisms underlying these changes in neural organization are discussed. SPONSORSHIP::This study was supported by Spinal Cord Research Foundation, the Paralyzed Veterans of America.Spinal Cord (2005) 43, 14-21. doi:10.1038/sj.sc.3101656; Published online 3 August 2004 [ABSTRACT FROM AUTHOR]

Although changes in the soleus H-reflex (an electrical analog of the tendon jerk) with age have been examined in a number of studies, some controversy remains. Also, the effect of age on inhibitory reflexes has received little attention. The purpose of this paper was to examine some excitatory and inhibitory reflexes systematically in healthy human subjects having a wide range of ages. We confirmed that both the maximum H-reflex (Hmax) and the maximum M-wave (Mmax) (from direct stimulation of motor axons) decrease gradually with age. The decrease in Hmax was larger so the Hmax/Mmax ratio decreased dramatically with age. Interestingly, the modulation of the H-reflex during walking was essentially the same at all ages, suggesting that the pathways that modulate the H-reflex amplitude during walking are relatively well preserved during the aging process. We showed for the first time that the short-latency, reciprocal inhibitory pathways from the common peroneal nerve to soleus muscle and from the tibial nerve to the tibialis anterior muscle also decreased with age, when measured as a depression of ongoing voluntary activity. These results suggest that there may be a general decrease in excitability of spinal pathways with age. Thus, the use of age-matched controls is particularly important in assessing abnormalities resulting from disorders that occur primarily in the elderly. [ABSTRACT FROM AUTHOR]

Everyday actions invariably consist of a combination of discrete and rhythmic elements within or across joints. The study investigated constraints arising from the co-occurrence of the two actions in a two-joint task and how endpoint trajectories are shaped due to these action elements at the joint level. The task consisted of an elbow oscillation in the plane that was to be merged with a fast discrete adduction or abduction in the shoulder triggered by an auditory signal. The task was performed with and without explicit instruction about the joint involvement. Two hypotheses were tested: (1) kinematic constraints for the coupling of discrete and rhythmic elements arise at the neuro-muscular level, such that EMG bursts of the discrete and rhythmic movement have a tendency to synchronize. This effect was documented previously in a comparable single-joint task. (2) The merging of the two elements is constrained by intersegmental torques such that initiation and performance of the discrete movement utilizes interaction torques. This hypothesis rests on the assumption that the CNS has an internal model of the limb dynamics and exploits passive torques. Key results support hypothesis 1: (i) the discrete action’s initiation at the shoulder was constrained to a preferred phase of the ongoing elbow oscillation. (ii) The rhythmic elbow movement showed a systematic phase advance during the discrete shoulder shift, similar to those reported for the single-joint variant of the task. Reaction times of the discrete movement were longer and peak velocities slower than reported for isolated discrete movements, due to the simultaneous presence of the oscillation. (iii) Interaction torques acting from the elbow onto the shoulder joint were not selectively exploited for the acceleration of the discrete shoulder movement. Indirectly however, hypothesis 2 also found support: torques at the elbow generated compensatory muscle activity in the shoulder that stabilized the stationary joint. It was this rhythmic activity that posed the direct constraints on the initiation of the discrete movement. [Copyright &y& Elsevier]