The effects of intra-oral pain on motor cortex neuroplasticity associated with short-term novel tongue-protrusion training in humans

Unravelling the effect of experimental pain on the corticomotor system using transcranial magnetic stimulation and electroencephalography

The interaction between pain and the motor system is well-known, with past studies showing that pain can alter corticomotor excitability and have deleterious effects on motor learning. The aim of this study was to better understand the cortical mechanisms underlying the interaction between pain and the motor system. Experimental pain was induced on 19 young and healthy participants using capsaicin cream, applied on the middle volar part of the left forearm. The effect of pain on brain activity and on the corticomotor system was assessed with electroencephalography (EEG) and transcranial magnetic stimulation (TMS), respectively. Compared to baseline, resting state brain activity significantly increased after capsaicin application in the central cuneus (theta frequency), left dorsolateral prefrontal cortex (alpha frequency), and left cuneus and right insula (beta frequency). A pain-evoked increase in the right primary motor cortex (M1) activity was also observed (beta frequency), but only among participants who showed a reduction in corticospinal output (as depicted by TMS recruitment curves). These participants further showed greater beta M1-cuneus connectivity than the other participants. These findings indicate that pain-evoked increases in M1 beta power are intimately tied to changes in the corticospinal system, and provide evidence that beta M1-cuneus connectivity is related to the corticomotor alterations induced by pain. The differential pattern of response observed in our participants suggest that the effect of pain on the motor system is variable from on individual to another; an observation that could have important clinical implications for rehabilitation professionals working with pain patients.

Effect of Experimental Hand Pain on Training-Induced Changes in Motor Performance and Corticospinal Excitability

Pain influences plasticity within the sensorimotor system and the aim of this study was to assess the effect of pain on changes in motor performance and corticospinal excitability during training for a novel motor task. A total of 30 subjects were allocated to one of two groups (Pain, NoPain) and performed ten training blocks of a visually-guided isometric pinch task. Each block consisted of 15 force sequences, and subjects modulated the force applied to a transducer in order to reach one of five target forces. Pain was induced by applying capsaicin cream to the thumb. Motor performance was assessed by a skill index that measured shifts in the speed–accuracy trade-off function. Neurophysiological measures were taken from the first dorsal interosseous using transcranial magnetic stimulation. Overall, the Pain group performed better throughout the training (p = 0.03), but both groups showed similar improvements across training blocks (p < 0.001), and there was no significant interaction. Corticospinal excitability in the NoPain group increased halfway through the training, but this was not observed in the Pain group (Time × Group interaction; p = 0.01). These results suggest that, even when pain does not negatively impact on the acquisition of a novel motor task, it can affect training-related changes in corticospinal excitability.

Effect of a brief episode of experimental muscle pain on jaw movement and jaw-muscle activity during chewing

The aims of this study were to determine whether: (i) the jaw motor system develops a new pattern of jaw movement and/or jaw-muscle activity after resolution of an acute episode of jaw-muscle pain; and (ii) if jaw-muscle activity and jaw-movement features change progressively with repetition of a chewing sequence. Jaw movement and jaw muscle (masseter, anterior temporalis, and digastric) activity were recorded during free and rate-standardized chewing in eight asymptomatic participants (pain infusion group), before and at three time blocks up to 45 min after a single 0.2-ml bolus infusion of 5% hypertonic saline into the right masseter muscle. The same procedure, without infusion, was performed in another eight participants (control group). There were no significant main effects of group on jaw movement and muscle activity, suggesting that there were no persistent post-pain effects on chewing. Across groups, repetitions of free and unstandardized chewing movements were associated with progressive increases in velocity and amplitude of jaw movement and masseter and temporalis electromyographic (EMG) activity. These findings suggest that factors unrelated to pain, such as practice effects, may be playing a role in the changes in jaw movement and jaw-muscle activity observed after resolution of an acute episode of jaw-muscle pain.

Interactive virtual feedback improves gait motor imagery after spinal cord injury: An exploratory study

Purpose: Motor imagery can improve motor function and reduce pain. This is relevant to individuals with spinal cord injury (SCI) in whom motor dysfunction and neuropathic pain are prevalent. However, therapy efficacy could be dependent on motor imagery ability, and a clear understanding of how motor imagery might be facilitated is currently lacking. Thus, the aim of the present study was to assess the immediate effects of interactive virtual feedback on motor imagery performance after SCI.

Methods: Nine individuals with a traumatic SCI participated in the experiment. Motor imagery tasks consisted of forward (i.e. simpler) and backward (i.e. more complex) walking while receiving interactive versus static virtual feedback. Motor imagery performance (vividness, effort and speed), neuropathic pain intensity and feasibility (immersion, distraction, side-effects) were assessed.

Results: During interactive feedback trials, motor imagery vividness and speed were significantly higher and effort was significantly lower as compared static feedback trials. No change in neuropathic pain was observed. Adverse effects were minor, and immersion was reported to be good.

Conclusions: This exploratory study showed that interactive virtual walking was feasible and facilitated motor imagery performance. The response to motor imagery interventions after SCI might be improved by using interactive virtual feedback.

Pain Induced during Both the Acquisition and Retention Phases of Locomotor Adaptation Does Not Interfere with Improvements in Motor Performance

Cutaneous pain experienced during locomotor training was previously reported to interfere with retention assessed in pain-free conditions. To determine whether this interference reflects consolidation deficits or a difficulty to transfer motor skills acquired in the presence of pain to a pain-free context, this study evaluated the effect of pain induced during both the acquisition and retention phases of locomotor learning. Healthy participants performed a locomotor adaptation task (robotized orthosis perturbing ankle movements during swing) on two consecutive days. Capsaicin cream was applied around participants' ankle on both days for the Pain group, while the Control group was always pain-free. Changes in movement errors caused by the perturbation were measured to assess global motor performance; temporal distribution of errors and electromyographic activity were used to characterize motor strategies. Pain did not interfere with global performance during the acquisition or the retention phases but was associated with a shift in movement error center of gravity to later in the swing phase, suggesting a reduction in anticipatory strategy. Therefore, previously reported retention deficits could be explained by contextual changes between acquisition and retention tests. This difficulty in transferring skills from one context to another could be due to pain-related changes in motor strategy.

Pain and motor processing in the human cerebellum

Pain-related adaptations in movement require a network architecture that allows for integration across pain and motor circuits. Previous studies addressing this issue have focused on cortical areas such as the midcingulate cortex. Here, we focus on pain and motor processing in the human cerebellum. The goal of this study was to identify areas of activation in the cerebellum, which are common to pain and motor processing, and to determine whether the activation is limited to the superior and inferior cerebellar motor maps or extends into multimodal areas of the posterior cerebellum. Our observations identified overlapping activity in left and right lobules VI and VIIb during pain and motor processing. Activation in these multimodal regions persisted when pain and motor processes were combined within the same trial, and activation in contralateral left lobule VIIb persisted when stimulation was controlled for. Functional connectivity analyses revealed significant correlations in the BOLD time series between multimodal cerebellar regions and sensorimotor regions in the cerebrum including anterior midcingulate cortex, supplementary motor area, and thalamus. The current findings are the first to show multimodal processing in lobules VI and VIIb for motor control and pain processing and suggest that the posterior cerebellum may be important in understanding pain-related adaptations in motor control.

Exploring the effects of synchronous pharyngeal electrical stimulation with swallowing carbonated water on cortical excitability in the human pharyngeal motor system

BACKGROUND

Previous reports have revealed that excitation of human pharyngeal motor cortex can be induced by pharyngeal electrical stimulation (PES) and swallowing carbonated water (CW). This study investigated whether combining PES with swallowing (of still water, SW or CW) can potentiate this excitation in either cortical and/or brain stem areas assessed with transcranial and transcutaneous magnetic stimulation (TMS).

METHODS

Fourteen healthy volunteers participated and were intubated with an intraluminal catheter to record pharyngeal electromyography and deliver PES. Each participant underwent baseline corticopharyngeal, hand and craniobulbar motor-evoked potential (MEP) measurements. Subjects were then randomized to receive each of four 10-min interventions (PES only, ShamPES+CW, PES+CW, and PES+SW). Corticobulbar, craniobulbar and hand MEPs were then remeasured for up to 60 min and data analyzed using anova and post hoc t-tests.

KEY RESULTS

A two-way rmanova for Interventions × Time-point showed a significant corticopharyngeal interaction (p = 0.010). One-way anova with post hoc t-tests indicated significant cortical changes with PES only at 45 (p = 0.038) and 60 min (p = 0.023) and ShamPES+CW immediately (p = 0.008) but not with PES+CW or PES+SW. By contrast, there were immediate craniobulbar amplitude changes only with PES+CW (p = 0.020) which were not sustained.

CONCLUSIONS & INFERENCES

We conclude that only PES produced long-term changes in corticopharyngeal excitability whereas combination stimuli were less effective. Our data suggest that PES alone rather than in combination, may be better for the patients who have difficulty in performing voluntary swallows.

Interactive effect of acute pain and motor learning acquisition on sensorimotor integration and motor learning outcomes

Previous work has demonstrated differential changes in early somatosensory evoked potentials (SEPs) when motor learning acquisition occurred in the presence of acute pain; however, the learning task was insufficiently complex to determine how these underlying neurophysiological differences impacted learning acquisition and retention. To address this limitation, we have utilized a complex motor task in conjunction with SEPs. Two groups of 12 participants (n = 24) were randomly assigned to either a capsaicin (capsaicin cream) or a control (inert lotion) group. SEP amplitudes were collected at baseline, after application, and after motor learning acquisition. Participants performed a motor acquisition task followed by a pain-free retention task within 24-48 h. After motor learning acquisition, the amplitude of the N20 SEP peak significantly increased (P < 0.05) and the N24 SEP peak significantly decreased (P < 0.001) for the control group while the N18 SEP peak significantly decreased (P < 0.01) for the capsaicin group. The N30 SEP peak was significantly increased (P < 0.001) after motor learning acquisition for both groups. The P25 SEP peak decreased significantly (P < 0.05) after the application of capsaicin cream. Both groups improved in accuracy after motor learning acquisition (P < 0.001). The capsaicin group outperformed the control group before motor learning acquisition (P < 0.05) and after motor learning acquisition (P < 0.05) and approached significance at retention (P = 0.06). Improved motor learning in the presence of capsaicin provides support for the enhancement of motor learning while in acute pain. In addition, the changes in SEP peak amplitudes suggest that early SEP changes reflect neurophysiological alterations accompanying both motor learning and mild acute pain.

Effects of Prolonged and Acute Muscle Pain on the Force Control Strategy During Isometric Contractions

Musculoskeletal pain is associated with multiple adaptions in movement control. This study aimed to determine whether changes in movement control acquired during acute pain are maintained over days of pain exposure. On day 0, the extensor carpi radialis brevis muscle of healthy participants was injected with nerve growth factor (NGF) to induce persistent movement-evoked pain (n = 13) or isotonic saline as a control (n = 13). On day 2, short-lasting pain was induced by injection of hypertonic saline into extensor carpi radialis brevis muscles of all participants. Three-dimensional force components were recorded during submaximal isometric wrist extensions on day 0, day 4, and before, during, and after saline-induced pain on day 2. Standard deviation (variation of task-related force) and total excursion of center of pressure (variation of force direction) were assessed. Maximal movement-evoked pain was 3.3 ± .4 (0-10 numeric scale) in the NGF-group on day 2 whereas maximum saline-induced pain was 6.8 ± .3 cm (10-cm visual analog scale). The difference in centroid position of force direction relative to day 0 was greater in the NGF group than in the control group (P < .05) on day 2 (before saline-induced pain) and day 4, reflecting changes in tangential force direction used to achieve the task. During saline-induced pain in both groups, tangential and task-related force variation was greater than before and after saline-induced pain (P < .05).

PERSPECTIVE

Persistent movement-evoked pain changes force direction from the pain-free direction. Acute pain leads to increased variation in force direction irrespective of persistent movement-evoked pain preceding the acutely painful event. These differences provide novel insight into the search for and consolidation of new motor strategies in the presence of pain.

The Rationale for Exercise in the Management of Pain in Parkinson's Disease

Pain is a distressing non-motor symptom experienced by up to 85% of people with Parkinson’s disease (PD), yet it is often untreated. This pain is likely to be influenced by many factors, including the disease process, PD impairments as well as co-existing musculoskeletal and/or neuropathic pain conditions. Expert opinion recommends that exercise is included as one component of pain management programs; however, the effect of exercise on pain in this population is unclear. This review presents evidence describing the potential influence of exercise on the pain-related pathophysiological processes present in PD. Emerging evidence from both animal and human studies suggests that exercise might contribute to neuroplasticity and neuro-restoration by increasing brain neurotrophic factors, synaptic strength and angiogenesis, as well as stimulating neurogenesis and improving metabolism and the immune response. These changes may be beneficial in improving the central processing of pain. There is also evidence that exercise can activate both the dopaminergic and non-dopaminergic pain inhibitory pathways, suggesting that exercise may help to modulate the experience of pain in PD. Whilst clinical data on the effects of exercise for pain relief in people with PD are scarce, and are urgently needed, preliminary guidelines are presented for exercise prescription for the management of central neuropathic, peripheral neuropathic and musculoskeletal pain in PD.

Experimental tonic hand pain modulates the corticospinal plasticity induced by a subsequent hand deafferentation

Sensorimotor reorganization is believed to play an important role in the development and maintenance of phantom limb pain, but pain itself might modulate sensorimotor plasticity induced by deafferentation. Clinical and basic research support this idea, as pain prior to amputation increases the risk of developing post-amputation pain. The aim of this study was to examine the influence of experimental tonic cutaneous hand pain on the plasticity induced by temporary ischemic hand deafferentation. Sixteen healthy subjects participated in two experimental sessions (Pain, No Pain) in which transcranial magnetic stimulation was used to assess corticospinal excitability in two forearm muscles (flexor carpi radialis and flexor digitorum superficialis) before (T0, T10, T20, and T40) and after (T60 and T75) inflation of a cuff around the wrist. The cuff was inflated at T45 in both sessions and in the Pain session capsaicin cream was applied on the dorsum of the hand at T5. Corticospinal excitability was significantly greater during the Post-inflation phase (p=0.002) and increased similarly in both muscles (p=0.861). Importantly, the excitability increase in the Post-inflation phase was greater for the Pain than the No-Pain condition (p=0.006). Post-hoc analyses revealed a significant difference between the two conditions during the Post-inflation phase (p=0.030) but no difference during the Pre-inflation phase (p=0.601). In other words, the corticospinal facilitation was greater when pain was present prior to cuff inflation. These results indicate that pain can modulate the plasticity induced by another event, and could partially explain the sensorimotor reorganization often reported in chronic pain populations.

Effect of local versus remote tonic heat pain during training on acquisition and retention of a finger-tapping sequence task

Although pain is present in a large proportion of patients receiving rehabilitation, its impact on motor learning is still unclear, especially in the case of neuropathic pain that is not tightly linked to specific movements. The aim of this study was to determine the effect of local and remote tonic cutaneous heat pain applied during training on motor learning of a finger-tapping sequence task. Forty-five healthy participants, randomized to the control, local pain or remote pain groups, were trained to perform an explicit finger motor sequence of five items as fast as possible. During the 10 training blocks (30 s each), local pain and remote pain groups received a heat pain stimulus on the wrist or leg, respectively. Performance was tested in the absence of pain in all groups before (baseline), immediately after (post-immediate), 60 min after (post-60 min) and 24 h after training (post-24 h) to assess both acquisition and next-day retention. Speed increased over time from baseline to post-24 h (p < 0.001), without any significant effect of group (p = 0.804) or time × group interaction (p = 0.385), indicating that the acquisition and retention were not affected by the presence of pain during training. No changes were observed on error rates, which were very low even at baseline. These results with experimental heat pain suggest that the ability to relearn finger sequence should not be affected by concomitant neuropathic pain in neurorehabilitation. However, these results need to be validated in the context of chronic pain, by including pain as a co-variable in motor rehabilitation trials.

Dental Occlusal Changes Induce Motor Cortex Neuroplasticity

Modification to the dental occlusion may alter oral sensorimotor functions. Restorative treatments aim to restore sensorimotor functions; however, it is unclear why some patients fail to adapt to the restoration and remain with sensorimotor complaints. The face primary motor cortex (face-M1) is involved in the generation and control of orofacial movements. Altered sensory inputs or motor function can induce face-M1 neuroplasticity. We took advantage of the continuous eruption of the incisors in Sprague-Dawley rats and used intracortical microstimulation (ICMS) to map the jaw and tongue motor representations in face-M1. Specifically, we tested the hypothesis that multiple trimming of the right mandibular incisor, to keep it out of occlusal contacts for 7 d, and subsequent incisor eruption and restoration of occlusal contacts, can alter the ICMS-defined features of jaw and tongue motor representations (i.e., neuroplasticity). On days 1, 3, 5, and 7, the trim and trim-recovered groups had 1 to 2 mm of incisal trimming of the incisor; a sham trim group had buccal surface trimming with no occlusal changes; and a naive group had no treatment. Systematic mapping was performed on day 8 in the naive, trim, and sham trim groups and on day 14 in the trim-recovered group. In the trim group, the tongue onset latency was shorter in the left face-M1 than in the right face-M1 ( P < .001). In the trim-recovered group, the number of tongue sites and jaw/tongue overlapping sites was greater in the left face-M1 than in the right face-M1 ( P = 0.0032, 0.0016, respectively), and the center of gravity was deeper in the left than in the right face-M1 ( P = 0.026). Therefore, incisor trimming and subsequent restoration of occlusal contacts induced face-M1 neuroplasticity, reflected in significant disparities between the left and right face-M1 in some ICMS-defined features of the tongue motor representations. Such neuroplasticity may reflect or contribute to subjects’ ability to adapt their oral sensorimotor functions to an altered dental occlusion.

Tonic pain experienced during locomotor training impairs retention despite normal performance during acquisition

Many patients are in pain when they receive gait training during rehabilitation. Based on animal studies, it has been proposed that central sensitization associated to nociception (maladaptive plasticity) and plasticity related to the sensorimotor learning (adaptive plasticity) share similar neural mechanisms and compete with each other. The aim of this study was to evaluate whether experimental tonic pain influences motor learning (acquisition and next-day retention) of a new locomotor task. Thirty healthy human subjects performed a locomotor adaptation task (perturbing force field applied to the ankle during swing using a robotized orthosis) on 2 consecutive days. Learning was assessed using kinematic measures (peak and mean absolute plantarflexion errors) and electromyographic (EMG) activity. Half of the participants performed the locomotor adaptation task with pain on Day 1 (capsaicin cream around the ankle), while the task was performed pain-free for all subjects on Day 2 to assess retention. Pain had no significant effect on baseline gait parameters nor on performance during the locomotor adaptation task (for either kinematic or EMG measures) on Day 1. Despite this apparently normal motor acquisition, pain-free Day 2 performance was markedly and significantly impaired in the Pain group, indicating that pain during training had an impact on the retention of motor memories (interfering with consolidation and/or retrieval). These results suggest that the same motor rehabilitation intervention could be less effective if administered in the presence of pain.

Comprehensive physiotherapy exercise programme or advice for chronic whiplash (PROMISE): a pragmatic randomised controlled trial

BACKGROUND

Evidence suggests that brief physiotherapy programmes are as effective for acute whiplash-associated disorders as more comprehensive programmes; however, whether this also holds true for chronic whiplash-associated disorders is unknown. We aimed to estimate the effectiveness of a comprehensive exercise programme delivered by physiotherapists compared with advice in people with a chronic whiplash-associated disorder.

METHODS

PROMISE is a two group, pragmatic randomised controlled trial in patients with chronic (>3 months and <5 years) grade 1 or 2 whiplash-associated disorder. Participants were randomly assigned by a computer-generated randomisation schedule to receive either the comprehensive exercise programme (20 sessions) or advice (one session and telephone support). Sealed opaque envelopes were used to conceal allocation. The primary outcome was pain intensity measured on a 0-10 scale. Outcomes were measured at baseline, 14 weeks, 6 months, and 12 months by a masked assessor. Analysis was by intention to treat, and treatment effects were calculated with linear mixed models. The trial is registered with the Australian New Zealand Clinical Trials Registry, number ACTRN12609000825257.

FINDINGS

172 participants were allocated to either the comprehensive exercise programme (n=86) or advice group (n=86); 157 (91%) were followed up at 14 weeks, 145 (84%) at 6 months, and 150 (87%) at 12 months. A comprehensive exercise programme was not more effective than advice alone for pain reduction in the participants. At 14 weeks the treatment effect on a 0-10 pain scale was 0·0 (95% CI -0·7 to 0·7), at 6 months 0·2 (-0·5 to 1·0), and at 12 months -0·1 (-0·8 to 0·6). CNS hyperexcitability and symptoms of post-traumatic stress did not modify the effect of treatment. We recorded no serious adverse events.

INTERPRETATION

We have shown that simple advice is equally as effective as a more intense and comprehensive physiotherapy exercise programme. The need to identify effective and affordable strategies to prevent and treat acute through to chronic whiplash associated disorders is an important health priority. Future avenues of research might include improving understanding of the mechanisms responsible for persistent pain and disability, investigating the effectiveness and timing of drugs, and study of content and delivery of education and advice.

FUNDING

The National Health and Medical Research Council of Australia, Motor Accidents Authority of New South Wales, and Motor Accident Insurance Commission of Queensland.

Effect of tonic pain on motor acquisition and retention while learning to reach in a force field

Most patients receiving intensive rehabilitation to improve their upper limb function experience pain. Despite this, the impact of pain on the ability to learn a specific motor task is still unknown. The aim of this study was to determine whether the presence of experimental tonic pain interferes with the acquisition and retention stages of motor learning associated with training in a reaching task. Twenty-nine healthy subjects were randomized to either a Control or Pain Group (receiving topical capsaicin cream on the upper arm during training on Day 1). On two consecutive days, subjects made ballistic movements towards two targets (NEAR/FAR) using a robotized exoskeleton. On Day 1, the task was performed without (baseline) and with a force field (adaptation). The adaptation task was repeated on Day 2. Task performance was assessed using index distance from the target at the end of the reaching movement. Motor planning was assessed using initial angle of deviation of index trajectory from a straight line to the target. Results show that tonic pain did not affect baseline reaching. Both groups improved task performance across time (p<0.001), but the Pain group showed a larger final error (under-compensation) than the Control group for the FAR target (p = 0.030) during both acquisition and retention. Moreover, a Group x Time interaction (p = 0.028) was observed on initial angle of deviation, suggesting that subjects with Pain made larger adjustments in the feedforward component of the movement over time. Interestingly, behaviour of the Pain group was very stable from the end of Day 1 (with pain) to the beginning of Day 2 (pain-free), indicating that the differences observed could not solely be explained by the impact of pain on immediate performance. This suggests that if people learn to move differently in the presence of pain, they might maintain this altered strategy over time.

The effect of experimental pain on motor training performance and sensorimotor integration

Experimental pain is known to affect neuroplasticity of the motor cortex as well as motor performance, but less is known about neuroplasticity of somatosensory processing in the presence of pain. Early somatosensory evoked potentials (SEPs) provide a mechanism for investigating alterations in sensory processing and sensorimotor integration (SMI). The overall aim of this study was to investigate the interactive effects of acute pain, motor training, and sensorimotor processing. Two groups of twelve participants (N = 24) were randomly assigned to either an intervention (capsaicin cream) or placebo (inert lotion) group. SEP amplitudes were collected by stimulation of the median nerve at baseline, post-application and post-motor training. Participants performed a motor sequence task while reaction time and accuracy data were recorded. The amplitude of the P22-N24 complex was significantly increased following motor training for both groups F(2,23) = 3.533, p < 0.05, while Friedman's test for the P22-N30 complex showed a significant increase in the intervention group [χ(2) (df = 2, p = 0.016) = 8.2], with no significant change in the placebo group. Following motor training, reaction time was significantly decreased for both groups F(1,23) = 59.575, p < 0.01 and overall accuracy differed by group [χ(2) (df = 3, p < 0.001) = 19.86], with post hoc testing indicating that the intervention group improved in accuracy following motor training [χ(2) (df = 1, p = 0.001) = 11.77] while the placebo group had worse accuracy [χ(2) (df = 1, p = 0.006) = 7.67]. The improved performance in the presence of capsaicin provides support for the enhancement of knowledge acquisition with the presence of nontarget stimuli. In addition, the increase in SEP peak amplitudes suggests that early SEP changes are markers of SMI changes accompanying motor training and acute pain.

Isotonic resistance jaw exercise alters jaw muscle coordination during jaw movements

The aim was to investigate the effects of isotonic resistance exercise on the electro-myographic (EMG) activity of the jaw muscles during standardised jaw movements. In 12 asymptomatic adults surface EMG activity was recorded from the anterior temporalis and masseter muscles bilaterally and the right anterior digastric muscle during right lateral jaw movements that tracked a target. Participants were randomly assigned to a Control group or an Exercise group. Jaw movement and EMG activity were collected (i) at baseline, before the exercise task (pre-exercise); (ii) immediately after the exercise task (isotonic resistance at 60% MVC against right lateral jaw movements); (iii) after 4 weeks of a home-based exercise programme; and, (iv) at 8-weeks follow-up. There were no significant within-subject or between-group differences in the velocity and amplitude of the right lateral jaw movements either within or between data collection sessions (P > 0.05). However, over the 8 weeks of the study, three of the tested EMG variables (EMG Duration, Time to Peak EMG from EMG Onset, and Time to Peak EMG activity relative to Movement Onset) showed significant (P < 0.05) differences in the five tested muscles. Many of the significant changes occurred in the Control group, while the Exercise group tended to maintain the majority of the tested variables at pre-exercise baseline values. The data suggest a level of variability between recording sessions in the recruitment patterns of some of the muscles of mastication for the production of the same right lateral jaw movement and that isotonic resistance exercise may reduce this variability.

Influence of position and stimulation parameters on intracortical inhibition and facilitation in human tongue motor cortex

Paired-pulse transcranial magnetic stimulation (ppTMS) can be used to assess short-interval intracortical inhibitory (SICI) and facilitatory (ICF) networks. Many methodological parameters may however influence the outcome. The aim of the study was to examine the influence of body positions (recline and supine), inter-stimulus intervals (ISI) between the test stimulus (TS) and conditioning stimulus (CS) and intensities of the TS and CS on the degree of SICI and ICF. In studies 1 and 2, fourteen and seventeen healthy volunteers participated respectively. ppTMS was applied over the "hot-spot" of the tongue motor cortex and motor evoked potentials (MEPs) were recorded from contralateral tongue muscles. In study 1, single pulse and three ppTMS ISIs, 2, 10, and 15ms, were applied 8 times each in three blocks (TS: 120%, 140% and 160% of resting motor threshold (rMT); CS: 80% of rMT) in two different body positions (recline and supine) randomly. In study 2, single pulse and four ppTMS ISIs, 2, 2.5, 3, and 3.5ms, were applied 8 times each in randomized order in two blocks (CS: 70% and 80% of rMT; TS: 120% of rMT). There was a significant effect of body position (P=0.049), TS intensities (P<0.001) and ISIs (P<0.001) and interaction between intensity and ISIs (P=0.042) in study 1. In study 2, there was a significant effect of ISI (P<0.001) but not CS intensity (P=0.984) on MEP amplitude. These results may be applied in future studies on the mechanisms of cortical plasticity in the tongue motor pathways using ppTMS and SICI and ICF.

Does movement variability increase or decrease when a simple wrist task is performed during acute wrist extensor muscle pain?

PURPOSE

The goal of complex tasks can be maintained despite variability in the movements of the multiple body segments involved in the task (VAR(elements)). This variability increases in acute pain and may enable the nervous system to search for less painful/injurious movement options. It is unclear whether VAR(elements) increases when pain challenges simple tasks with fewer movement options, yet maintain successful attainment of the goal. We hypothesised that during acute pain related to a simple movement: (1) the task goal would be maintained; (2) VAR(elements) would be increased; and (3) if VAR(elements) increased during pain, it would decrease over time.

METHODS

Movements of the right wrist/forearm were recorded with a three-dimensional motion analysis system and during a repetitive radial-ulnar deviation task between two target angle ranges (the task goal). We measured success of attaining the goal (repetitions that reached the target range and total absolute error in degrees), and variability in the motion of wrist flexion-extension and forearm pronation-supination (VAR(elements)). Fourteen healthy participants performed the task in one session before, during, and after wrist extensor muscle pain induced with hypertonic saline, and in another session without pain.

RESULTS

The task goal was maintained during acute pain. However, VAR(elements) in other motion planes either reduced (pronation-supination) or did not change (flexion-extension). Thus, variability of task elements is constrained, rather than increased, in simple tasks.

CONCLUSIONS

These data suggest the nervous system adapts simple tasks with limited degrees of freedom by reduction of VAR(elements) rather than the increase observed for more complex tasks.

Specific neck training induces sustained corticomotor hyperexcitability as assessed by motor evoked potentials

STUDY DESIGN

Experimental investigation of short-term and long-term corticomotor effects of specific neck training, coordination training, and no training.

OBJECTIVE

To determine the effects of different training programs on the motor neurons controlling the neck muscles as well as the effects of training on muscle strength and muscle fatigue, and the correlations between corticomotor control and motor learning.

SUMMARY OF BACKGROUND DATA

Training is usually recommended for unspecific neck pain and consists of neck and upper body coordination, strengthening, and endurance exercises. However, it is unclear which type of training is the most effective. No studies have previously investigated the neural effect of neck training and the possible differential effect of specific versus coordination training on corticomotor control.

METHODS

Transcranial magnetic stimulation and electromyography were used to elicit and monitor motor evoked potentials (MEPs) from the trapezius and thumb muscles before and 30 minutes, 1 hour, and 7 days after training. Parameters measured were MEP amplitude, MEP latency, strength, learning effects, and muscle fatigue.

RESULTS

Only specific neck training yielded a 67% increase in MEP amplitudes for up to 7 days after training compared with baseline (P < 0.001). No significant changes were seen after coordination training, no training, and in the within-subject control muscle. The mean muscle strength increased immediately after specific neck training from 56.6 to 61 kg (P < 0.001). No subjective or objective measures of fatigue were observed.

CONCLUSION

Specific neck training induced a sustained hyperexcitability of motor neurons controlling the neck muscles compared with coordination training and controls. These findings may prove valuable in the process of developing more effective clinical training programs for unspecific neck pain.

Prism adaptation alters spatial remapping in healthy individuals: evidence from double-step saccades

The visual system is able to represent and integrate large amounts of information as we move our gaze across a scene. This process, called spatial remapping, enables the construction of a stable representation of our visual environment despite constantly changing retinal images. Converging evidence implicates the parietal lobes in this process, with the right hemisphere having a dominant role. Indeed, lesions to the right parietal lobe (e.g., leading to hemispatial neglect) frequently result in deficits in spatial remapping. Research has demonstrated that recalibrating visual, proprioceptive and motor reference frames using prism adaptation ameliorates neglect symptoms and induces neglect-like performance in healthy people - one example of the capacity for rapid neural plasticity in response to new sensory demands. Because of the influence of prism adaptation on parietal functions, the present research investigates whether prism adaptation alters spatial remapping in healthy individuals. To this end twenty-eight undergraduates completed blocks of a double-step saccade (DSS) task after sham adaptation and adaptation to leftward- or rightward-shifting prisms. The results were consistent with an impairment in spatial remapping for left visual field targets following adaptation to leftward-shifting prisms. These results suggest that temporarily realigning spatial representations using sensory-motor adaptation alters right-hemisphere remapping processes in healthy individuals. The implications for the possible mechanisms of the amelioration of hemispatial neglect after prism adaptation are discussed.

Considerations in the physical rehabilitation of patients with whiplash-associated disorders

STUDY DESIGN

Review of research identifying physical impairments in the neuromuscular system in subjects with whiplash-associated disorders.

OBJECTIVE

Review the impairments in movement and neuromuscular function toward constructing research informed exercise programs.

SUMMARY OF BACKGROUND DATA

Pain and injury to the musculoskeletal system result in loss of motion and impaired neuromuscular function which impacts on functional activities, work and quality of life. Therapeutic exercise is a mainstay of rehabilitation, but the nature of the exercises prescribed are currently various and the effect sizes of current programs for patients with whiplash-associated disorders are modest at best.

METHODS

A review was undertaken of research investigating the changes in cervical motion and neuromuscular function to better inform exercise prescription and identify areas for future research. RESULTS.: Reduced range of movement as well as pathological movement patterns (reduced acceleration and velocity, reduced smoothness and irregular axes of neck movement) have been documented in subjects with whiplash-associated disorders. In relation to neuromuscular control, changes have been demonstrated in neck muscles' spatial and temporal relationships as well as in their strength and endurance. The presence or not and the extent of changes is highly variable between individuals and appears to have some relationship to pain intensity. It appears that there is a need for specificity in exercise prescription to address particular impairments rather than the use of generic programs. High pain intensity can modify effects of a therapeutic exercise program.

CONCLUSION

Pain and injury result in reorganization of the motor control strategies of neck muscles and movement. Further research is required to determine if outcomes after a whiplash injury can be improved by using research informed, individually prescribed exercise programs matched to the individual's presentation. Research into best methods of pain management is also required to facilitate physical rehabilitation.

Toward optimal early management after whiplash injury to lessen the rate of transition to chronicity: discussion paper 5

STUDY DESIGN

Expert debate and synthesis of research to inform future management approaches for acute whiplash disorders.

OBJECTIVE

To identify a research agenda toward improving outcomes for acute whiplash-injured individuals to lessen the incidence of transition to chronicity.

SUMMARY OF BACKGROUND DATA

International figures are concordant, estimating that 50% of individuals recover from pain and disability within 3 to 6 months of a whiplash injury. The remainder report continuing symptoms up to 1 to 2 years or longer postinjury. As no management approach to date has improved recovery rates, new clinical/research directions are required for early management of whiplash-injured patients.

METHODS

A group of multidisciplinary researchers critically debated evidence and current research concerning whiplash from biological, psychological, and social perspectives toward informing future research directions for management of acute whiplash.

RESULTS

It was recognized that effective treatments for acute whiplash are constrained by a limited understanding of causes of whiplash-associated disorders. Acute whiplash presentations are heterogeneous leading to the proposal that a research priority was development of a triage system based on modifiable prognostic indicators and clinical features to better inform individualized early management decisions. Other priorities identified included researching effective early pain management for individuals presenting with moderate to high levels of pain; development of best education/information for acute whiplash; testing the efficacy of stratified and individualized rehabilitation, researching modes of delivery considering psychosocial modulators of pain and disability; and the timing, nature, and mode of delivery of cognitive-behavioral therapies. Directions were highlighted for future biomechanical research into injury prevention.

CONCLUSION

The burden of whiplash injuries, the high rate of transition to chronicity, and evidence of limited effects of current management on transition rates demand new directions in evaluation and management. Several directions have been proposed for future research, which reflect the potential multifaceted dimensions of an acute whiplash disorder.

Tip of the tongue selectivity and motor learning in the palatal area

This study assessed the ability of the tongue tip to accurately select intraoral targets embedded in an upper palatal tongue-computer interface, using 18 able-bodied volunteers. Four performance measures, based on modifications to Fitts's Law, were determined for three different tongue-computer interface layouts. The layouts differed with respect to number and location of the targets in the palatal interface. Assessment of intraoral target selection speed and accuracy revealed that performance was indeed dependent on the location and distance between the targets. Performances were faster and more accurate for targets located farther away from the base of the tongue in comparison to posterior and medial targets. A regression model was built, which predicted intraoral target selection time based on target location and movement amplitude better than the predicted by using a standard Fitts's Law model. A 30% improvement in the speed and accuracy over three daily practice sessions of 30 min emphasizes the remarkable motor learning abilities of the tongue musculature and provides further evidence that the tongue is useful for operating computer-interface technologies.

Interactions between Pain and the Motor Cortex: Insights from Research on Phantom Limb Pain and Complex Regional Pain Syndrome

PURPOSE

Pain is a significantly disabling problem that often interacts with other deficits during the rehabilitation process. The aim of this paper is to review evidence of interactions between pain and the motor cortex in order to attempt to answer the following questions: (1) Does acute pain interfere with motor-cortex activity? (2) Does chronic pain interfere with motor-cortex activity, and, conversely, does motor-cortex plasticity contribute to chronic pain? (3) Can the induction of motor plasticity by means of motor-cortex stimulation decrease pain? (4) Can motor training result in both motor-cortex reorganization and pain relief?

SUMMARY OF KEY POINTS

Acute experimental pain has been clearly shown to exert an inhibitory influence over the motor cortex, which can interfere with motor learning capacities. Current evidence also suggests a relationship between chronic pain and motor-cortex reorganization, but it is still unclear whether one causes the other. However, there is growing evidence that interventions aimed at normalizing motor-cortex organization can lead to pain relief.

CONCLUSIONS

Interactions between pain and the motor cortex are complex, and more studies are needed to understand these interactions in our patients, as well as to develop optimal rehabilitative strategies.

Pain and motor control: From the laboratory to rehabilitation

Movement is changed in pain and is the target of clinical interventions. Yet the understanding of the physiological basis for movement adaptation in pain remains limited. Contemporary theories are relatively simplistic and fall short of providing an explanation for the variety of permutations of changes in movement control identified in clinical and experimental contexts. The link between current theories and rehabilitation is weak at best. New theories are required that both account for the breadth of changes in motor control in pain and provide direction for development and refinement of clinical interventions. This paper describes an expanded theory of the motor adaptation to pain to address these two issues. The new theory, based on clinical and experimental data argues that: activity is redistributed within and between muscles rather than stereotypical inhibition or excitation of muscles; modifies the mechanical behaviour in a variable manner with the objective to "protect" the tissues from further pain or injury, or threatened pain or injury; involves changes at multiple levels of the motor system that may be complementary, additive or competitive; and has short-term benefit, but with potential long-term consequences due to factors such as increased load, decreased movement, and decreased variability. This expanded theory provides guidance for rehabilitation directed at alleviating a mechanical contribution to the recurrence and persistence of pain that must be balanced with other aspects of a multifaceted intervention that includes management of psychosocial aspects of the pain experience.

Corticomotor plasticity induced by tongue-task training in humans: a longitudinal fMRI study

Corticomotor pathways may undergo neuroplastic changes in response to acquisition of new motor skills. Little is known about the motor control strategies for learning new tongue tasks. The aim of this study was to investigate the longitudinal effect of novel tongue-task training on corticomotor neuroplasticity. Thirteen healthy, right-handed men, aged 24-35 years (mean age ± SD: 27.3 ± 0.3 years), performed a training task consisting of standardized tongue protrusion onto a force transducer. The tongue task consisted of a relax-protrude-hold-relax cycle with 1.0 N as the target at the hold phase lasting for 1.5 s. Subjects repeated this task for 1 h. Functional magnetic resonance imaging was carried out before the tongue-task training (baseline), 1-h after the training, and one-day and one-week follow-up. During scanning, the subjects performed tongue protrusion in blocks interspersed with rest. A region-of-interest (ROI) approach and an explorative search were implemented for the analysis of corticomotor activity across conditions. All subjects completed the tongue-task training (mean success rate 43.0 ± 13.2%). In the baseline condition, tongue protrusion resulted in bilateral activity in regions most typically associated with a motor task including medial frontal gyrus (supplementary motor area [SMA]), precentral gyrus (tongue motor cortex), putamen, thalamus, and cerebellum. The ROI analysis revealed increased activity in the precentral gyrus already 1 h post-training. One day after the training, increased activity was observed in the precentral gyrus, SMA, putamen, and cerebellum. No increase was found 1 week after training. Correlation analyses between changes in success rates and changes in the numbers of voxels showed robust associations for left Area 4a in primary motor cortex 1 h, 1 day, and 1 week after the tongue-task training and for the left Area 4p in primary motor cortex and the left lateral premotor cortex 1 day after the training. In the unrestricted analysis, increased activity was found in the parahippocampal gyrus 1 h after the tongue-task training and remained for a week. Decreased activity was found in right post-central and middle frontal gyri 1 h and 1 week post-training. The results verified the involvement of specific corticomotor areas in response to tongue protrusion. Short-term tongue-task training was associated with longer-lasting (up to 1 week) changes in motor-related brain activity. The results suggested that primary motor areas are involved in the early and late stages, while other motor areas mainly are engaged in the later stage of corticomotor neuroplasticity of the tongue.