Untrained Side Research Articles

Corticospinal excitability of untrained side depends on the type of motor task and degree of improvement in motor function

Unimanual motor tasks change the corticospinal excitability of the trained and untrained side. However, whether the motor task type influences the modulation of the corticospinal excitability of the untrained side remains unclear. This study aimed to clarify the effects of motor tasks on the corticospinal excitability of the untrained side and the relationship between the excitability and motor function. In Experiment I, we measured the corticospinal excitability of the untrained side and motor function after 10 min of motor training in two conditions (gripping task and ball rotation task). The gripping task decreased the excitability. In contrast, excitability remained unchanged after the ball rotation task; further, the modulation of excitability and motor function showed a correlation. In Experiment II, we measured the corticospinal excitability of the untrained side and motor function after two sessions of the ball rotation task. The excitability increased, but motor function remained unchanged after the first session, whereas the excitability decreased to the level observed before training, and motor function improved after the second session. We suggest that the training condition modulates the corticospinal excitability of the untrained side and that this is related to the modulation of motor function.

Acupuncture Therapy on the Recovery of Badminton Players' Knee Joint Muscle Injury

At present, a large number of data or research results have proved that after a cycle of electroacupuncture at specific acupoints and hand acupuncture at specific acupoints, etc., not only can increase the muscle strength on the acupuncture side, but also improve the non-acupuncture or The strength of the muscles on the untrained side. This is the cross migration of muscle strength training. This phenomenon can occur in the upper limb muscles of the human body, and it can also occur in the lower limb muscles. With the deepening of various studies, this phenomenon has been used in the clinical practice of rehabilitation treatment and has achieved good results. In this context, acupuncture therapy provides new rehabilitation ideas for the recovery of related muscle damage and strengthening of muscle strength in badminton, and it can also enrich traditional resistance training or drug rehabilitation treatment methods.

Cortical, Corticospinal, and Reticulospinal Contributions to Strength Training.

Following a program of resistance training, there are neural and muscular contributions to the gain in strength. Here, we measured changes in important central motor pathways during strength training in 2 female macaque monkeys. Animals were trained to pull a handle with one arm; weights could be added to increase load. On each day, motor-evoked potentials in upper limb muscles were first measured after stimulation of the primary motor cortex (M1), corticospinal tract (CST), and reticulospinal tract (RST). Monkeys then completed 50 trials with weights progressively increased over 8-9 weeks (final weight ∼6 kg, close to the animal's body weight). Muscle responses to M1 and RST stimulation increased during strength training; there were no increases in CST responses. Changes persisted during a 2 week washout period without weights. After a further 3 months of strength training, an experiment under anesthesia mapped potential responses to CST and RST stimulation in the cervical enlargement of the spinal cord. We distinguished the early axonal volley and later spinal synaptic field potentials, and used the slope of the relationship between these at different stimulus intensities as a measure of spinal input-output gain. Spinal gain was increased on the trained compared with the untrained side of the cord within the intermediate zone and motor nuclei for RST, but not CST, stimulation. We conclude that neural adaptations to strength training involve adaptations in the RST, as well as intracortical circuits within M1. By contrast, there appears to be little contribution from the CST.SIGNIFICANCE STATEMENT We provide the first report of a strength training intervention in nonhuman primates. Our results indicate that strength training is associated with neural adaptations in intracortical and reticulospinal circuits, whereas corticospinal and motoneuronal adaptations are not dominant factors.

The effect of unilateral training on contralateral limb power in young women and men.

The purpose of this study was to determine the effect of training of one side of the body on the muscle torques and power output on the trained and untrained side. Seventeen female and twenty-two male students were subject to a four-week knee joint power training regimen on a specially designed stand. The subjects were divided into two groups: a training group (female – N = 11 and male – N = 16) and a control group (female – N = 6 and male – N = 6). Effectiveness of power training on the stand described previously was estimated based on bilateral knee torque and power under static and isokinetic conditions. The experiment lasted for 39 days and was preceded by preliminary studies (pre-training). Control measurements in training groups were made after four weeks of training (post-training) and after the next two weeks (de-training). Power training caused an insignificant increase in force and power in both groups for the untrained leg and a significant increase in RMS EMG. Therefore, the study confirmed the hypothesis that resistance training performed in dynamic conditions can affect the contralateral limb and may also trigger delayed adaptations to training conditions during the detraining phase. Sex differences in adaptation to power training are not clear; however, the differences in gains in contralateral effects between men and women were not confirmed.

Perspectives on neurorehabilitation of unilateral impairments through cross-education

Background: Cross-education is being increasingly investigated as an unconventional, exercise-based intervention to manage severely lateralized weakness. To date, however, cross-education seems more important to research than clinical practice.Aim: To provide foundation and context for an informed employment of cross-education in severely or predominantly unilateral weakness or motor impairment.Method: Qualitative, narrative commentary.Results: Based on the comprehensive overview on contralateral strength training approaches to hemiplegia and unilateral weakness in stroke survivors performed by Russell and colleagues as well as on our experiences in multiple sclerosis, there is a potential for cross-education as a useful training approach to hemiplegia and unilateral weakness in stroke survivors and multiple sclerosis patients and, overall, in neurorehabilitation. However, some limitations of this non-conventional approach have to be pointed out, such as the apparent lack of translation of the performance gains of the weaker untrained side into functional improvement, particularly for the lower limb.Conclusion: Cross-education may serve as a viable option for those patients presenting severe unilateral weakness who are not able to fully exercise their weaker side directly. However, it should not be recommended straightaway if the training goal is to improve outcomes other than strength. As such, contralateral training may prove as a primer to establish a minimum level of strength that may suffice to sustain direct training, which has been proved to prompt more meaningful functional changes.Implications for rehabilitationCross-education consists of training the stronger limb to increase strength in the untrained weaker homologous muscles.This unconventional strategy is receiving increasing attention for possible applications in neurological populations exhibiting severe unilateral impairment.For those patients who are not able to fully exercise their weaker side it may represent a viable exercise option.However, cross-education should not be recommended straightaway if the training goal is to improve outcomes other than strength.

Neurophysiological Analysis of Intermanual Transfer in Motor Learning.

The purpose of this study was to examine the effect of motor training on motor imagery (MI), by comparing motor performance and motor cortex excitability changes with and without intermanual transfer of motor learning. Intermanual transfer was investigated in terms of excitability changes in the motor cortex and motor performance from right hand training to left hand performance. Participants were assigned to a transfer training group and a control group. We recorded motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS), applied to the left extensor carpi radialis (ECR) both with and without intermanual transfer. The results showed that after learning by the right hand, MEPs decreased during left hand MI. MEPs during MI were significantly decreased by unilateral training in the transfer training group. Since intermanual transfer plays an important role in stabilizing performance by the contralateral side, this result suggests that unilateral training decreases MEPs during MI on the contralateral side. In the control group, without right hand training, MEPs significantly increased after left hand training during MI. In the trained side, we found increased excitability in the agonist muscle area of the primary motor cortex. However, in the untrained side, excitability decreased in the homonymous muscle area of the primary motor cortex. This constitutes an increase in inhibitory effects and suggests that excitability changes in the respective neural circuit contribute to skilled performance by the ipsilateral and contralateral sides in the same motor task.

Influence of mirror therapy and motor imagery on intermanual transfer effects in upper-limb prosthesis training of healthy participants: A randomized pre-posttest study.

The effect that a motor skill trained on one side can lead to improvement in the untrained side is called intermanual transfer. Intermanual transfer can help enhance upper limb prosthetic training. To determine the influence of mirror therapy and motor imagery on intermanual transfer in upper limb prosthesis training, a pseudo-randomized clinical trial, single blinded, with a pre-posttest design was used. Forty-seven able-bodied, right-handed participants were pseudo-randomly assigned to two training groups and one control group. One training group undertook an intermanual transfer training program, using an upper-limb prosthetic simulator with added mirror therapy and motor imagery. The second training group completed only the intermanual transfer training program. The control group completed a sham training: a dummy training without using the prosthesis simulator. The program lasted five consecutive days. To determine the improvement in skill, a test was administered before, immediately after, and six days after the training program. Training used the “unaffected” arm; tests were performed with the “affected” arm, resembling the amputated limb. Movement time, the time from the beginning of the movement until completion of the task; hand opening, the duration of the maximum prosthetic hand opening; and grip-force control, the deviation from the required force during a tracking task. No intermanual transfer effects were found: neither the intermanual transfer training program, nor the additional mirror therapy and motor imagery affected prosthesis skills. A limitation of the study was that the training program was applied to able-bodied subjects instead of patients with an amputation. Contrary to previous studies, no intermanual transfer effects were found. Additional mirror therapy and motor imagery did not ameliorate intermanual transfer effects.

Unilateral wrist extension training after stroke improves strength and neural plasticity in both arms.

Stroke induces bilateral neurological impairment and muscle weakness yielding neurologically more (MA; paretic) and less affected (LA; non-paretic) sides. "Cross-education" refers to training one side of the body to increase strength in the same muscles on the untrained side. Past work showed dorsiflexion training of the LA side produced bilateral strength increases after stroke. The current study explored the presence and extent of cross-education after arm strength training in chronic stroke. Twenty-four chronic stroke participants completed 5 weeks of maximal wrist extension training using their LA arm. Maximal voluntary contraction force, arm motor impairment and functional performance were measured before and after training. Both spinal cord plasticity (n = 12: reciprocal inhibition and cutaneous reflexes, University of Victoria) and cortical plasticity (n = 12: cortical silent period, short-interval intracortical inhibition, intracortical facilitation and transcallosal inhibition, University of British Columbia) were assessed. Five weeks after training, 20 participants completed a follow-up maximal wrist extension retention test. LA wrist extension force increased 42% and MA by 35%. Strength gains were maintained in the follow-up test. Clinically meaningful increases in Fugl-Meyer scores were noted in four participants. Muscle activation was correlated with cutaneous reflex amplitudes after training in the MA arm. LA cortical silent period and transcallosal inhibition from both hemispheres significantly decreased after training. This study shows that high-intensity training with the neurologically less affected "non-paretic" arm can improve strength bilaterally and alter both spinal and cortical plasticity. The extent to which this plasticity can be enhanced or functionally exploited remains to be examined.

Can the Newly Learnt Gait Pattern after Running Retraining be Translated to Untrained Conditions?

Running retraining is reported to be effective in impact loading control and injury prevention. During running retraining, biomechanics metrics, such as tibial shock, from one side of the body is usually provided while the participant is running at a controlled test speed. Whether participants are able to translate the newly learnt gait pattern to untrained conditions (e.g., untrained side of the limb and untrained speeds) remains unanswered. PURPOSE: To compare the tibial shock of the participants’ untrained limb and at untrained running speeds before and after a course of running retraining. METHODS: Ten runners underwent a running retraining program as described by Crowell & Davis (2011). Before and after the program, their tibial shock from both limbs were measured using wireless accelerometers when they were running at the training speed (TS), 110% of TS and 90% of TS. The peak tibial shock during the last 20 footfalls in each 3-minute trial were extracted for analyses. RESULTS: The effect of gait retraining did not interact with test speeds (p=0.699) but it interacted with limb side (p<0.05). We found a reduction in the tibial shock on the trained limb at all test speeds (p=0.001-0.008; Figure 1). However, we only observed a trend of tibial shock reduction on the untrained side (p=0.074-0.098; Figure 1). CONCLUSIONS: The current running retraining protocol may not be fully optimized as the newly learnt gait pattern may not be completely translated to untrained conditions.Figure 1: Peak tibial shock before and after running retraining at three speedsTS: Training speed* Significantly reduced compared to pre-training test

Neurophysiological adaptations in the untrained side in conjunction with cross-education of muscle strength: a systematic review and meta-analysis.

We reviewed the evidence from randomized controlled trials (RCTs) focusing on the neurophysiological adaptations in the untrained side associated with cross-education of strength (CE) and pooled data into definite effect estimates for neurophysiological variables assessed in chronic CE studies. Furthermore, scoping directions for future research were provided to enhance the homogeneity and comparability of studies investigating the neural responses to CE. The magnitude of CE was 21.1 ± 18.2% (mean ± SD; P < 0.0001) in 22 RCTs ( n = 467 subjects) that measured at least 1 neurophysiological variable in the untrained side, including the following: electromyography (EMG; 14 studies); motor evoked potential (MEP; 8 studies); short-interval intracortical inhibition (SICI), recruitment curve, and M wave (6 studies); cortical silent period (cSP; 5 studies); interhemispheric inhibition, intracortical facilitation (ICF), and H reflex (2 studies); and V wave, short-interval ICF, short-latency afferent inhibition, and long-latency afferent inhibition (1 study). Only EMG, MEP, ICF, cSP, and SICI could be included in the meta-analysis (18 studies, n = 387). EMG ( P = 0.26, n = 235) and MEP amplitude ( P = 0.11, n = 145) did not change in the untrained limb after CE. cSP duration ( P = 0.02, n = 114) and SICI ( P = 0.001, n = 95) decreased in the untrained hemisphere according to body region and type and intensity of training. The magnitude of CE did not correlate with changes in these transcranial magnetic stimulation (TMS) measures. The design of this meta-analytical study and the lack of correlations prevented the ability to link mechanistically the observed neurophysiological changes to CE. Notwithstanding the limited amount of data available for pooling, the use of TMS to assess the ipsilateral neurophysiological responses to unilateral training still confirms the central neural origin hypothesis of chronic CE induced by strength training. However, how these neural adaptations contribute to CE remains unclear.

Unilateral strength training with and without a mirror to improve motor function after stroke: Past, present, and future

Unilateral resistance training not only strengthens muscles on the trained side but also the homologous muscles on the untrained side. This phenomenon is called cross-education and was first observed in 1894. Since then, many studies have been conducted in neurologically intact persons but the potential of cross-education for people with unilateral orthopaedic and neurological impairments remains largely unexplored. In this commentary, we highlight the potential of cross-education in the rehabilitation after stroke. Current clinical practice in stroke rehabilitation is to train the more-affected side but people with a severe hemiparesis are often not able to train this side due to muscle weakness and limited range of motion. Resistance training of the less-affected side might be a great tool to improve muscle strength and motor function of the more-affected side. Mirror therapy, where a mirror reflection of the less-affected side creates the illusion that the more affected side is exercising, could even further augment these cross-education benefits. Three functional networks (i.e., attentional resources, the mirror-neuron system, and the motor network) play a role in cross-education with and without a mirror and induce neuroplasticity in the brain that can help people who have had a stroke in their recovery. The use of inter-limb mechanisms in the rehabilitation from unilateral impairments has to be exploited further and should be incorporated in the standard protocols for neurologic and musculoskeletal rehabilitation.

P251 Effect of long term comprehensive training of the left hand in strongly right handed participants: Reduction of interhemispheric asymmetry in intracortical facilitation (ICF)

Introduction The effect of intracortical facilititation (ICF) is independent from hemispheric dominance and handedness (Baumer et al., 2007). Short term training selectively increases excitability over the contralateral primary motor cortex (M1c) of the trained hand (e.g. Lotze et al., 2003). M1-excitability measurements after long-term training (several weeks) are rare but – to our knowledge – are even absent for ICF-parameters. Objectives To evaluate effects of ICF during a two week comprehensive period of training of the left hand in strongly right handed healthy participants. Materials and ethods Thirteen strongly right-handed healthy participants (23 ± 3.5 years; 6 women) underwent a two-week arm ability training (AAT) for their left, nondominant hand for one hour per day (Platz, 2004). Performance increase was expressed as percentual changes over time and averaged over all eight AAT-tasks. Focal TMS was delivered to the optimal scalp position for activation of the musculus abductor policis brevis (APB) of each hand using a figure-of-eight coil. Resting motor threshold (rMT) and intracortical facilitation (ICF; test stimulus intensity 120% rMT; conditioning stimulus 80% rMT; interstimulus interval 10 ms) were used as measures of corticomotor excitability. Results Training resulted in considerable improvement of the trained left (30 ± 3.5%) hand, but – to a lesser extent – also the non-trained right hand (18 ± 5.4%) performance. RMT was not altered over time. For ICF we found a strong time effect in ANOVA; but post hoc t-tests showed only a relevant decrease over time for the untrained side (T(12) = 3.33; p = 0.006; Fig. 1). Conclusion Our study showed no significant changes in ICF for the trained hand side, but a decrease for the non trained hand’s motor cortex. It has been demonstrated that the interaction between an increase of unilateral movement and 10 h unilateral immobilization of the other hand is critical for excitability effects over M1c (Avanzino et al., 2011). We argue that interhemispheric changes induced by unilateral limb training of the non-dominant hand might be multifactorial; here we observed an increased interhemispheric balance in ICF after training the less experienced, and presumably in spontaneous behavior less intensively used hand. Download : Download high-res image (410KB) Download : Download full-size image

An effect of multisensory training on visual processing (Commentary on Grasso etal. (2016)).

An effect of multisensory training on visual processing (Commentary on Grasso etal. (2016)).

Mirror Training Augments the Cross-education of Strength and Affects Inhibitory Paths.

Unilateral strength training strengthens not only the muscles on the trained side but also the homologous muscles on the untrained side; however, the magnitude of this interlimb cross-education is modest. We tested the hypothesis that heightened sensory feedback by mirror viewing the exercising hand would augment cross education by modulating neuronal excitability. Healthy adults were randomized into a mirror training group (MG, N = 11) and a no-mirror training group (NMG, N = 12) and performed 640 shortening muscle contractions of the right wrist flexors at 80% maximum voluntary contraction (MVC) during 15 sessions for 3 wk. Maximal strength and specific transcranial magnetic stimulation metrics of neuronal excitability, measured in the mirror and no-mirror setup at rest and during unilateral contractions at 60% MVC, were assessed before and after the strength intervention. Trained wrist flexor MVC increased 72% across groups, whereas cross-education was higher for the MG (61%) than NMG (34%, P = 0.047). The MG showed a reduction (15%-16%) in the contralateral silent period duration measured from the contracting left-untrained flexor carpi radialis, whereas the NMG showed an increase (12%, P ≤ 0.030). Interhemispheric inhibition, measured from the trained to the untrained primary motor cortex, increased in the MG (11%) but decreased in the NMG (15%) when measured in the mirror setup at rest (P = 0.048). Other transcranial magnetic stimulation measures did not change. Viewing the exercising hand in a mirror can augment the cross-education effect. The use of a mirror in future studies can potentially accelerate functional recovery from unilateral impairment due to stroke or upper limb fracture.

Intermanual transfer effect in young children after training in a complex skill: mechanistic, pseudorandomized, pretest-posttest study.

Intermanual transfer implies that motor skills learned on one side of the body transfer to the untrained side. This effect was previously noted in adults practicing with a prosthesis simulator. The study objective was to determine whether intermanual transfer is present in children practicing prosthetic handling. A mechanistic, pseudorandomized, pretest-posttest design was used. The study was conducted in a primary school in the Netherlands. The participants were children who were able-bodied (N=48; 25 boys, 23 girls; mean age=5.1 years) and randomly assigned to an experimental group or a control group. The experimental group performed 5 training sessions using a prosthesis simulator on the training arm. Before (pretest), immediately after (posttest), and 6 days after (retention test) the training program, their ability to handle the prosthesis with the contralateral (test) arm was measured. The control group only performed the tests. Half of the children performed the tests with the dominant hand, and the other half performed the tests with the nondominant hand. During the tests, movement time and control of force were measured. An interaction effect of group by test was found for movement time. Post hoc tests revealed significant improvement in the experimental group between the posttest and the retention test. No force control effect was found. Only children who were able-bodied were included. Measurements should have been masked and obtained without tester interference. The fact that 4 children whose results were slower than the mean result discontinued training may have biased the findings. The intermanual transfer effect was present in 5-year-old children undergoing training in prosthetic handling. After training of one hand, children's movement times for the other, untrained hand improved. This finding may be helpful for training children who are novice users of a prosthesis.

Effects of involuntary eccentric contraction training by neuromuscular electrical stimulation on the enhancement of muscle strength

BackgroundNeuromuscular electrical stimulation is well-known as a modality to improve the performance of neuromuscular system, but its clinical value on muscle strengthening remains equivocal. In this study, we designed a system for an involuntary eccentric contraction of biceps brachii muscles using continuous passive movement and commercial neuromuscular electrical stimulation devices. MethodsTo investigate the effects of involuntary eccentric contraction training by neuromuscular electrical stimulation on the enhancement of muscle strength, seven healthy men between the ages of 24 and 29years participated in this study. Participants were trained two times per week for 12weeks. Each exercise session was performed for 30min with no rest intervals. Isometric elbow flexion torque and biceps brachii muscle thickness were chosen as evaluation indices, and were measured at pre-/post-training. FindingsAfter the 12-week training, the isometric elbow flexion torque of the trained side significantly increased by approximately 23% compared to the initial performance (P<0.01). Meanwhile, the torque of the untrained side showed no significant change (P=0.862). During the 12-week training period, the biceps brachii muscle thickness of the trained side significantly increased by around 8% at rest and 16% at maximum voluntary contraction (P<0.01). InterpretationThe developed system and the technique show promising results, suggesting that it has the potential to be used to increase the muscle strength in patients with neuromuscular disease and to be implemented in design rehabilitative protocols.

LONG-TERM PLANTAR FLEXOR STIMULATION AFTER SPINAL CORD INJURY PREFERENTIALLY PRESERVES BONE MINERAL DENSITY IN THE POSTERIOR ASPECT OF THE DISTAL TIBIA

Purpose/Hypothesis: We have recently demonstrated that long-term electrical stimulation of the paralyzed plantar flexors yields a significant trabecular bone mineral density (BMD)-sparing effect (∼31%) at the distal tibia, a common fracture site after spinal cord injury (SCI) (Shields and Dudley-Javoroski, J Neurophys 2006). Because the plantar flexors lie posterior to the tibia, plantar flexor muscle activation may most adequately load the posterior aspect of the tibia, yielding superior BMD-sparing effects in this region. The purpose of the study is to determine whether long-term plantar flexor electrical stimulation yields a differential bone-sparing effect across the distal tibia cross-section. Number of Subjects: 3 men with motor/sensory complete SCI. Materials/Methods: Subjects completed >3 years of unilateral isometric plantar flexor electrical stimulation training. They subsequently underwent magnetic resonance imaging (MRI) and peripheral quantitative computed tomography (pQCT) of both lower limbs (average 4.7 years post-SCI/4.4 years of training). We devised a method to partition the tibia image into anterior and posterior regions for sub-sectional analysis, based on bony landmarks. Results: Distal tibia trabecular BMD was 27% higher in trained limbs than in untrained limbs. BMD differed only by 6.9% between the anterior and posterior regions of the untrained tibia. Conversely, in the trained tibia, BMD of the posterior region was 57.8% higher than the anterior region. BMD of the posterior region of the trained tibia was 235.7 mg/ccm, only 6% lower than previously-published non-SCI reference values (Eser et al, Bone 2004). One subject was unable to undergo MRI due to metal fragments in his torso. In the remaining 2 subjects, the trained soleus was slightly (5%) or considerably (28%) larger than the untrained soleus. However, hypertrophy of the trained limb deep flexors was more uniform (34% and 37% larger than the untrained side). The gastrocnemius showed no hypertrophy in the trained limbs. Tibialis anterior was 19% larger in the trained limbs for both subjects. Conclusions: The BMD-sparing effect of long-term plantar flexor electrical stimulation was most evident in the posterior aspect of the distal tibia, suggesting the possibility of greater bone compressive loads in the posterior than the anterior region. A large training effect (hypertrophy) of the deep plantar flexor muscles supports this observation. Hypertrophy of trained-side tibialis anterior muscles (likely due to co-activation) was insufficient to offset the robust posterior tibia BMD-sparing effect of long-term plantar flexor training. Clinical Relevance: These findings support that long-term neuromuscular electrical stimulation may help preserve trabecular BMD in individuals with SCI. The BMD-sparing effect may be sensitive to the orientation of the compressive loads delivered by activated muscles. Physical therapists should consider using neuromuscular electrical stimulation of certain muscle groups to prevent the severe loss of bone following SCI.

The effect of submaximal eccentric isokinetic training on strength and cross sectional area of the human achilles tendon

This study was designed to investigate the effects of six weeks submaximal eccentric training on concentric and eccentric isokinetic peak torque and cross sectional area (CSA) (muscle and tendon) of calf muscle. Six men and four women volunteered as subjects for this study. Peak torque values for plantar flexion were determined at 30°/s, 60°/s and 90°/s (concentric and eccentric) using a Cybex® Norm before the training, 3 weeks after the beginning and at the end of the sixth week. Following training, peak torque increased in the concentric and eccentric modes in both the trained (p < 0.001) and untrained (p < 0.01) side. No significant change in CSA was noted. The results of this study indicate that after 6 weeks of submaximal eccentric training the strength gained was not completely specific to the contraction type used in training. Transfer of training took place. Neither muscle nor tendon hypertrophy was observed, suggesting the involvement of neural adaptation.

Movement dysfunction following repetitive hand opening and closing: anatomical analysis in Owl monkeys.

Repetitive strain injuries are thought to result from biomechanical stress and tissue microtrauma. The purpose of this study was to investigate the presence of local inflammation, scarring or anatomical variations of the flexor tendons and the median and ulnar nerves in four Owl monkeys behaviorally trained at a repetitive motor or sensory task. Three monkeys were trained to repetitively open and close a handpiece. The two monkeys that used rapid, stereotypical hand squeezing developed a task-specific movement dysfunction (one in 5 weeks and one in 24 weeks). The third monkey used a variable shoulder-pulling strategy and did not develop movement problems. The fourth monkey served as a control subject for the repetitive motor movements, trained on a repetitive sensory task, and did not develop a task-specific movement dysfunction. On dissection and histologic staining, there were no signs of active inflammation in the median nerve, the ulnar nerve, or the flexor tendons in any of the monkeys. However, the monkey that developed movement problems after 5 weeks of repetitive hand squeezing had an anatomical restriction of the flexor profundus tendon on the fourth digit of the trained side and the third digit of the untrained side. Reorganization of the representation of the hand on the contralateral somatosensory cortex (area 3b) was noted in the two monkeys that developed motor control problems and in the monkey performing the repetitive sensory task. These findings suggest that repetitive, stereotypical motor behaviors can lead to motor control problems without local signs of tendon or nerve inflammation. Preexisting anatomical restrictions may modify the time course for the development of movement dysfunction under conditions of stressful repetition. This animal model may simulate clinical focal hand dystonia (or occupational hand cramps) which can develop in human subjects who perform prolonged, repetitive, stereotypical movements.

Selective changes in AMPA receptors in rabbit cerebellum following classical conditioning of the eyelid-nictitating membrane response

α-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors are critically involved in several forms of synaptic plasticity proposed to be neural substrates for learning and memory, e.g., long-term potentiation and long-term depression (LTD). The present study was designed to determine changes in cerebellar AMPA receptors following classical conditioning of the eyeblink-nictitating membrane response (NMR) in the rabbit. Quantitative autoradiography was used to assess changes in ligand binding properties of cerebellar AMPA receptors following NMR conditioning elicited by pairing electrical stimulation of the pontine nuclei with an airpuff to the eye. [ 3 H ]AMPA and [ 3 H ]-6-cyano-7-nitroquinoxaline-2,3-dion (CNQX) binding were determined following preincubation of frozen–thawed brain tissue sections at 0 or 35°C. With 0°C preincubation, no significant differences in [ 3 H ]AMPA binding to cerebellar AMPA receptors were seen between any of the experimental groups tested. In contrast, preincubation at 35°C revealed significant decreases in [ 3 H ]AMPA binding to the trained side of the cerebellar cortex resulting from paired presentations of the conditioned and the unconditioned stimuli, while unpaired presentations of the stimuli resulted in no significant effect. With 35°C preincubation, there were no significant differences in [ 3 H ]CNQX binding between any of the experimental groups and no significant differences in [ 3 H ]AMPA binding in the untrained side of the cerebellum. These results indicate that NMR conditioning is associated with a selective modification of AMPA-receptor properties in brain structures involved in the storage of the associative memory. Furthermore, they support the hypothesis that cerebellar LTD, resulting from decreased synaptic efficacy at parallel fiber–Purkinje cell synapses mediated by a change in AMPA-receptor properties, is a form of synaptic plasticity that supports this type of learning.