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• The relation of spinal reflexes with leg motor function was tested in sub-acute and chronic stroke. • Severe spasticity is linked to heteronymous facilitation and disynaptic reciprocal inhibition in sub-acute stroke patients. • Spinal reflexes are potential biomarkers for spasticity and motor function. To assess the relationship between spinal reflexes and motor function in sub-acute (SAS) and chronic stroke (CS) patients. Twelve SAS and 16 CS patients underwent electrophysiological assessment of heteronymous facilitation (HF), heteronymous inhibition (HI), disynaptic reciprocal inhibition (DRI), and D1 inhibition (D1). The Fugl-Meyer Assessment Lower Extremity (FMA-LE) and modified Ashworth scale (MAS) were assessed. The relationship between spinal reflexes and motor function was examined in a cross-sectional manner. SAS patients were also longitudinally evaluated before and after intensive rehabilitation for approximately 2 months. SAS patients with triceps surae muscle spasticity (MAS ≥ 1) showed higher HF values (p = 0.03) than those without spasticity. SAS patients with quadriceps muscle spasticity showed higher HF values (p < 0.01); patients with hamstring muscle spasticity showed higher DRI value (disinhibition) (p < 0.01) than those without spasticity. CS patients showed no significant correlation between spinal reflexes and motor function. The longitudinal study revealed a significant correlation between increase in D1 inhibition and FMA-LE improvement in SAS patients (r = 0.69). The association between impaired spinal reflexes varies with the stage of stroke; HF and DRI may be spasticity indicators in SAS patients. Spinal reflexes as potential biomarkers may facilitate tailor-made rehabilitation of stroke patients. [ABSTRACT FROM AUTHOR]

Hyper-reflexia is occasionally seen in acute motor axonal neuropathy (AMAN), but its pathophysiology is unclear. We report a patient with AMAN following Campylobacter jejuni enteritis, who showed generalized hyper-reflexia, bilateral Hoffmann sign and right Babinski sign. MRI and transcranial magnetic stimulation of the motor cortex disclosed no corticospinal tract involvement. An extensive electrophysiological investigation documented α-motoneuron hyperexcitability and dysfunction of the interneuronal inhibitory circuits in the spinal anterior horn. We propose an immune-mediated damage of the spinal inhibitory interneuronal network as possible mechanism inducing hyper-reflexia in AMAN. [ABSTRACT FROM AUTHOR]

• A walking assistive device that targets ankle movements has been utilized. • Short-term intervention of the device decreased spinal cord reciprocal inhibition. • The device might be effective for regulating spinal cord excitability. One of the major problems with walking encountered by patients with spastic hemiplegia is diminished toe clearance due to spasticity of their leg muscles. To improve their walking, a specialized robot assist for ankle movements (RE-Gait) has been utilized. The present study examined the neurophysiological effects whether spinal cord reciprocal Ia inhibition (RI) in the leg was altered by using RE-Gait. Sixteen patients with a clinical diagnosis of stroke were divided into the two groups, RE-Gait walking group (Group R) and normal (controlled) walking group (Group C). In each group, they walked on a flat floor for 15 min with or without RE-Gait. The depression of soleus (Sol) H-reflexes conditioned by common peroneal nerve stimuli with the conditioning-test (C-T) intervals of 1, 2, 3, and 4 ms were assessed before and immediately after each walking session. After the intervention, the LSM (SE) of Sol H-reflex amplitude with 1, 2 and 3 ms C-T interval conditions were significantly decreased in group R (1 ms: 88.15 (4.60), 2 ms: 86.37 (4.60), 3 ms: 89.68 (4.62)) compared to group C (1 ms: 105.57 (4.56), 2 ms: 100.89 (4.58), 3 ms: 107.72 (4.58)) [1 ms: p = 0.012, 2 ms: p = 0.035, 3 ms: p = 0.011]. Walking assistive robot that targets ankle movements might be a new rehabilitation tool for regulating spinal cord excitability. [ABSTRACT FROM AUTHOR]

Highlights • Glutamatergic drive to the preBötzinger Complex is essential for respiratory rhythm. • Glutamatergic drive to the Bötzinger Complex contributes to respiratory phase timing. • Inspiratory premotor neurons receive continuous tonic excitatory inputs. • Bötzinger Complex neurons inhibit inspiratory premotor neurons during expiration. Abstract Glutamate is the predominant excitatory neurotransmitter in the ventral respiratory column; however, the contribution of glutamatergic excitation in the individual subregions to respiratory rhythm generation has not been fully delineated. In an adult, in vivo, decerebrate rabbit model during conditions of mild hyperoxic hypercapnia we blocked glutamatergic excitation using the receptor antagonists 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX) and d(–)-2-amino-5-phosphonopentanoic acid (AP5). Disfacilitation of the preBötzinger Complex caused a decrease in inspiratory and expiratory duration as well as peak phrenic amplitude and ultimately apnea. Disfacilitation of the Bötzinger Complex caused a decrease in inspiratory and expiratory duration; subsequent disfacilitation of the preBötzinger Complex resulted in complete loss of the respiratory pattern but maintained tonic inspiratory activity. We conclude that glutamatergic drive to the preBötzinger Complex is essential for respiratory rhythm generation. Glutamatergic drive to the Bötzinger Complex significantly affects inspiratory and expiratory phase duration. Bötzinger Complex neurons are responsible for maintaining the silent expiratory phase of the phrenic neurogram. [ABSTRACT FROM AUTHOR]

In the leg, amplitudes of cutaneous reflexes and reciprocal inhibition are significantly affected by joint and limb position. Comparatively little is known about such modulation in the arm. In this study, amplitudes of reciprocal inhibition (from median nerve stimulation near elbow) and cutaneous reflexes (from median or superficial radial nerve stimulation at the wrist) were measured in forearm muscle extensor carpi radialis with the hand pronated or neutral during graded voluntary activation. Significant correlations with muscle activation were found for reciprocal inhibition and cutaneous reflex amplitudes at both positions. Only cutaneous reflexes from superficial radial nerve were modulated by wrist position. This study reveals that effect of limb position is nerve-specific in cutaneous reflexes and not significant on reciprocal inhibition in the arm. This has implications for measurement and study design in those who have mobility and motor activation challenges (e.g. neurotrauma) that affect hand function. [ABSTRACT FROM AUTHOR]

Many central pattern generators (CPGs) are built on a basic circuit of reciprocally inhibitory neurons, the minimal configuration that can produce distinct rhythmic patterns for controlling antagonistic muscles. In this paper, we use a closed-loop to control the rhythm of a CPG model based on this minimal network architecture. The closed-loop adapts the maximum conductance of the inhibition to achieve a regularized rhythm departing from an otherwise highly irregular spiking–bursting activity. Our results show that the closed-loop conductance control can rapidly find the best connectivity that leads to the regularization goal. We also discuss several external stimuli that lead to regularized CPG rhythms. We argue that the proposed closed-loop approach can be used to control CPG rhythms in a wide variety of applications in experimental and theoretical research. [ABSTRACT FROM AUTHOR]

Highlights: [•] Unidirectional visual motion adaptation induces reciprocal inhibition of oppositely tuned directionally selective neurones. [•] Changes in neuronal excitability lasted at least 4min. [•] Provides direct cortical evidence in support of the waterfall illusion in humans. [Copyright &y& Elsevier]

Abstract: This article reviews the contributions of Ivan Michailovich Sechenov [1829–1905] to the neurophysiological concept of central inhibition. He first studied this concept in the frog and on himself. Later his trainees extended the study of central inhibition to other mammalian species. Outside his own country, Sechenov is better known for his prescient contributions to physiological psychology. In Russia, however, he is also revered as “the father of Russian physiology,” because of his contributions to neurophysiology and other aspects of physiology including blood gases and respiration, the physiology and biomechanics of movement, and general physiology concepts that appeared in his textbooks and later works he helped translate from largely German sources. After graduation from Moscow University Medical School in 1856 he spent 3½ years in Germany and Austria where he attended lectures and conducted research under the direction of several prominent physiologists and biochemists. In his subsequent academic career he held positions at universities in St. Petersburg (1860–1870; 1876–1888), Odessa (1871–1876) and Moscow (1890–1905). From 1860 onwards he was acclaimed as a physiologist in academic circles. He was also well known in Russian society for his public lectures on physiology and his views on physiological psychology. The latter resulted in him being branded “politically unreliable” by the tsarist bureaucracy from 1863 onwards. Sechenov's first (1862) study on central inhibition remains his most memorable. He delayed the withdrawal of a frog's foot from a weak acid solution by chemical or electrical stimulation of selected parts of the central nervous system. He also noted similar effects on his own hand during co-activation of other sensory inputs by tickling or teeth gnashing. [Copyright &y& Elsevier]

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]

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: 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]

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: 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]

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]

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]

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]

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]

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]

Posture influences the strength of spinal reflex circuits in healthy individuals. The purpose of this study was to determine the extent to which sitting and standing posture influences the strength of reciprocal Ia inhibition between ankle flexor and extensor muscles in individuals with incomplete spinal cord injury (SCI). Ten individuals with SCI and 15 healthy individuals participated in the study. Short-latency reciprocal inhibition was measured by conditioning the soleus H-reflex with stimulation of the common peroneal nerve. There was no significant difference in the strength of reciprocal Ia inhibition in sitting and standing positions in individuals with SCI. However, healthy individuals showed increased inhibition in a standing compared to a sitting position. The results suggest an impaired posture-dependent modulation of reciprocal Ia inhibition following SCI. [Copyright &y& Elsevier]

Objective: To test the hypothesis that besides impaired agonist facilitation, impaired antagonist inhibition also contributes to delayed initiation (akinesia) and slow execution (bradykinesia) of voluntary movements in Huntington''s disease.Methods: Fifteen patients with Huntington''s disease and 11 age-matched controls participated in the study. The amount of agonist facilitation was measured as the increase in soleus H-reflex amplitude prior to ballistic voluntary plantar flexion (soleus contraction). Antagonist inhibition was measured as the decrease in soleus H-reflex prior to ballisitic dorsiflexion (tibialis anterior (TA) contraction). The amount of agonist facilitation and antagonist inhibition was correlated with the time needed for motor initiation (reaction time) and movement execution (movement time).Results: Starting 50 ms prior to soleus contraction, soleus H-reflex increased in control subjects but less so in patients. Soleus H-reflexes decreased in controls 25 ms prior to TA contraction, while this antagonist inhibition was completely lacking in patients. Thus, patients with Huntington''s disease not only displayed reduced agonist facilitation, but impaired antagonist inhibition as well. Moreover, more impairment of antagonist inhibition correlated significantly with more severe akinesia and bradykinesia.Conclusions: Antagonist inhibition prior to and during agonist contractions is markedly impaired in Huntington''s disease. This impairment might contribute to motor slowness in these patients. [Copyright &y& Elsevier]

• We investigated the recruited neural circuits in motor point stimulation. • H-reflex was evoked in peripheral nerve stimulation but not motor point stimulation. • Motor point stimulation could induce antidromic firing of motor nerve, but not reciprocal inhibition. • Motor point stimulation primarily stimulate motor nerve but not Ia-sensory nerve. Electrical stimulation for inducing muscle contraction can be divided into peripheral nerve stimulation (PNS) and motor point stimulation (MPS). Although the neural pathways activated by PNS have been well studied, those by MPS are still unclear. Here we investigated whether MPS activates Ia-sensory nerves and induces antidromic firing of motor nerves. Ten able-bodied males and females participated in this study. We confirmed that soleus MPS did not induce the H-reflex while soleus PNS did. Furthermore, MPS of the tibialis anterior muscle did not induce the reciprocal inhibition of soleus muscle while PNS did. For testing the effect of MPS on motor neuron excitability, we examined the H-reflex modulation by soleus MPS. When the conditioning and test interval was under 100-ms and the conditioning stimulus intensity was above 30-mA, soleus MPS induced the H-reflex inhibition. This suggests that soleus MPS produces antidromic firing that can induce after-hyperpolarization. These results suggest that MPS predominantly activates the motor nerve without depolarizing the Ia-sensory nerve. Since MPS is applicable to larger number of muscles compared to PNS, utilizing MPS can lead to more versatile neuromodulation of the spinal cord. [ABSTRACT FROM AUTHOR]

This article reviews the contributions of the English neurophysiologist, Charles Scott Sherrington [1857–1952], and his Australian PhD trainee and collaborator, John Carew Eccles [1903–1997], to the concept of central inhibition in the spinal cord and brain. Both were awarded Nobel Prizes; Sherrington in 1932 for "discoveries regarding the function of neurons," and Eccles in 1963 for "discoveries concerning the ionic mechanisms involved in excitation and inhibition in central portions of the nerve cell membrane." Both spoke about central inhibition at their Nobel Prize Award Ceremonies. The subsequent publications of their talks were entitled "Inhibition as a coordinative factor" and "The ionic mechanism of postsynaptic inhibition", respectively. Sherrington's work on central inhibition spanned 41 years (1893–1934), and for Eccles 49 years (1928–1977). Sherrington first studied central inhibition by observing hind limb muscle responses to electrical (peripheral nerve) and mechanical (muscle) stimulation. He used muscle length and force measurements until the early 1900s and electromyography in the late 1920s. Eccles used these techniques while working with Sherrington, but later employed extracellular microelectrode recording in the spinal cord followed in 1951 by intracellular recording from spinal motoneurons. This considerably advanced our understanding of central inhibition. Sherrington's health was poor during his retirement years but he nonetheless made a small number of largely humanities contributions up to 1951, one year before his death at the age of 94. In contrast, Eccles retained his health and vigor until 3 years before his death and published prolifically on many subjects during his 22 years of official retirement. His last neuroscience article appeared in 1994 when he was 91. Despite poor health he continued thinking about his life-long interest, the mind-brain problem, and was attempting to complete his autobiography in the last years of his life. [ABSTRACT FROM AUTHOR]

Electrical stimulus, with duration starting at 0.1 ms and gradually increased to 1.0 ms, was used for eliciting the H reflex in 14 normal subjects and 19 patients with Parkinson''s disease (PD). In 71.1% of normal subjects and in 13.2% of PD patients the H reflex to M response threshold ratio (H/M TR) was <1 and the H reflex was obtained before the M response for all duration stimuli. For all stimulus durations a significant difference between the H/M TR in normal subjects and PD patients was found (t test 0.002–0.007). The duration effect was found to be highly significant—H/M TR for short stimulus duration was greater than for long stimulus durations (p<0.001). The optimal stimulus duration for evaluating H reflex behavior in PD patient was 0.2 ms.These very significant differences in behavior of the H reflex in PD patients could be used as another parameter in the assessment of extrapyramidal rigidity in PD patients. [Copyright &y& Elsevier]