Transcranial Static Magnetic Field Stimulation over the Primary Motor Cortex Induces Plastic Changes in Cortical Nociceptive Processing

Temporal Dynamics of Moderate-Intensity Transcranial Static Magnetic Stimulation in Young Adults

Background

Transcranial static magnetic stimulation (tSMS) as a new noninvasive brain stimulation (NIBS) technique is gradually gaining widespread attention. This study aims to investigate the effects of tSMS on the excitability of the somatosensory cortex in healthy adults.

Methods

Forty healthy volunteers were recruited and randomly assigned to either the intervention group (tSMS) or the control group (sham), with 20 participants in each. The intervention group received 30 min of 180 mT neodymium magnet stimulation at the C3 site, while the control group underwent sham stimulation with a non-magnetic cylinder. Electrodes were placed at the C3 and Fz sites according to the 10-20 system. Somatosensory evoked potentials (SEPs) N20 component amplitudes were measured at baseline, immediately after stimulation (0 - 2 min), 5 - 7 min, and 10 - 12 min post-stimulation to evaluate the effects on cortical excitability.

Results

Following 30 min of static magnetic stimulation, the SEP N20 component amplitude at the C3 site in the tSMS group decreased by an average of 13.2%, with a significant reduction of 13.7% within 0 - 2 min post-stimulation (P < 0.001). This decrease persisted at 5 - 7 min, with a reduction of 16.6% (P < 0.001), and diminished to 9.3% at 10 - 12 min (P = 0.034). Significant differences were observed between time points and groups (P = 0.003). In the control group, no significant changes were observed in SEP N20 component amplitude throughout the experiment (P = 0.382), and there was no significant difference between the two groups (P = 0.195).

Conclusions

These results confirm that a single session of tSMS effectively inhibits cortical excitability in the somatosensory cortex of young adults. This finding underscores the potential of tSMS as a promising, noninvasive brain stimulation technique with broad future applications.

Advances in Material-Assisted Electromagnetic Neural Stimulation

Bioelectricity plays a crucial role in organisms, being closely connected to neural activity and physiological processes. Disruptions in the nervous system can lead to chaotic ionic currents at the injured site, causing disturbances in the local cellular microenvironment, impairing biological pathways, and resulting in a loss of neural functions. Electromagnetic stimulation has the ability to generate internal currents, which can be utilized to counter tissue damage and aid in the restoration of movement in paralyzed limbs. By incorporating implanted materials, electromagnetic stimulation can be targeted more accurately, thereby significantly improving the effectiveness and safety of such interventions. Currently, there have been significant advancements in the development of numerous promising electromagnetic stimulation strategies with diverse materials. This review provides a comprehensive summary of the fundamental theories, neural stimulation modulating materials, material application strategies, and pre-clinical therapeutic effects associated with electromagnetic stimulation for neural repair. It offers a thorough analysis of current techniques that employ materials to enhance electromagnetic stimulation, as well as potential therapeutic strategies for future applications.

Effect of transcranial static magnetic stimulation over unilateral or bilateral motor association cortex on performance of simple and choice reaction time tasks

Background

Transcranial static magnetic stimulation (tSMS) is a non-invasive brain stimulation technique that place a strong neodymium magnet on scalp to reduce cortical excitability. We have recently developed a new tSMS device with three magnets placed close to each other (triple tSMS) and confirmed that this new device can produce a stronger and broader static magnetic field than the conventional single tSMS. The aim of the present study was to investigate the effect of the conventional single tSMS as well as triple tSMS over the unilateral or bilateral motor association cortex (MAC) on simple and choice reaction time (SRT and CRT) task performance.

Methods

There were two experiments: one involved the conventional tSMS, and the other involved the triple tSMS. In both experiments, right-handed healthy participants received each of the following stimulations for 20 min on different days: tSMS over the unilateral (left) MAC, tSMS over the bilateral MAC, and sham stimulation. The center of the stimulation device was set at the premotor cortex. The participants performed SRT and CRT tasks before, immediately after, and 15 min after the stimulation (Pre, Post 0, and Post 15). We evaluated RT, standard deviation (SD) of RT, and accuracy (error rate). Simulation was also performed to determine the spatial distribution of magnetic field induced by tSMS over the bilateral MAC.

Results

The spatial distribution of induced magnetic field was centered around the PMd for both tSMS systems, and the magnetic field reached multiple regions of the MAC as well as the sensorimotor cortices for triple tSMS. SD of CRT was significantly larger at Post 0 as compared to Pre when triple tSMS was applied to the bilateral MAC. No significant findings were noted for the other conditions or variables.

Discussion

We found that single tSMS over the unilateral or bilateral MAC did not affect performance of RT tasks, whereas triple tSMS over the bilateral MAC but not over the unilateral MAC increased variability of CRT. Our finding suggests that RT task performance can be modulated using triple tSMS.

Differential Effects of Transcranial Static Magnetic Stimulation Over Left and Right Dorsolateral Prefrontal Cortex on Brain Oscillatory Responses During a Working Memory Task

Transcranial static magnetic stimulation (tSMS) is known to influence behavioral and neural activities. However, although the left and right dorsolateral prefrontal cortex (DLPFC) are associated with different cognitive functions, there remains a lack of knowledge on a difference in the effects of tSMS on cognitive performance and related brain activity between left and right DLPFC stimulations. To address this knowledge gap, we examined how differently tSMS over the left and right DLPFC altered working memory performance and electroencephalographic oscillatory responses using a 2-back task, in which subjects monitor a sequence of stimuli and decide whether a presented stimulus matches the stimulus presented two trials previously. Fourteen healthy adults (five females) performed the 2-back task before, during (20 min after the start of stimulation), immediately after, and 15 min after three different stimulation conditions: tSMS over the left DLPFC, tSMS over the right DLPFC, and sham stimulation. Our preliminary results revealed that while tSMS over the left and right DLPFC impaired working memory performance to a similar extent, the impacts of tSMS on brain oscillatory responses were different between the left and right DLPFC stimulations. Specifically, tSMS over the left DLPFC increased the event-related synchronization in beta band whereas tSMS over the right DLPFC did not show such an effect. These findings support evidence that the left and right DLPFC play different roles in working memory and suggest that the neural mechanism underlying the impairment of working memory by tSMS can be different between left and right DLPFC stimulations.

Effects of transcranial static magnetic field stimulation over the left dorsolateral prefrontal cortex on random number generation

OBJECTIVE

Focal application of transcranial static magnetic field stimulation (tSMS) is a neuromodulation technique, with predominantly inhibitory effects when applied to the motor, somatosensory or visual cortex. Whether this approach can also transiently interact with dorsolateral prefrontal cortex (DLPFC) function remains unclear. The suppression of habitual or competitive responses is one of the core executive functions linked to DLPFC function. This study aimed to assess the impact of tSMS on the prefrontal contributions to inhibitory control and response selection by means of a RNG task.

METHODS

We applied 20 min of tSMS over the left DLPFC of healthy subjects, using a real/sham cross-over design, during performance of a RNG task. We used an index of randomness calculated with the measures of entropy and correlation to assess the impact of stimulation on DLPFC function.

RESULTS

The randomness index of the sequences generated during the tSMS intervention was significantly higher compared to those produced in the sham condition.

CONCLUSIONS

Our results indicate that application of tSMS transiently modulates specific functional brain networks in DLPFC, which indicate a potential use of tSMS for treatment of neuropsychiatric disorders.

SIGNIFICANCE

This study provides evidence for the capacity of tSMS for modulating DLPFC function.

Static magnetic field stimulation over motor cortex modulates resting functional connectivity in humans

Focal application of transcranial static magnetic field stimulation (tSMS) over the human motor cortex induces local changes in cortical excitability. Whether tSMS can also induce distant network effects, and how these local and distant effects may vary over time, is currently unknown. In this study, we applied 10 min tSMS over the left motor cortex of healthy subjects using a real/sham parallel design. To measure tSMS effects at the sensori-motor network level, we used resting-state fMRI. Real tSMS, but not sham, reduced functional connectivity within the stimulated sensori-motor network. This effect of tSMS showed time-dependency, returning to sham levels after the first 5 min of fMRI scanning. With 10 min real tSMS over the motor cortex we did not observe effects in other functional networks examined (default mode and visual system networks). In conclusion, 10 min of tSMS over a location within the sensori-motor network reduces functional connectivity within the same functional network.

Exploring the role of the left DLPFC in fatigue during unresisted rhythmic movements

Understanding central fatigue during motor activities is important in neuroscience and different medical fields. The central mechanisms of motor fatigue are known in depth for isometric muscle contractions; however, current knowledge about rhythmic movements and central fatigue is rather scarce. In this study, we explored the role of an executive area (left dorsolateral prefrontal cortex [DLPFC]) in fatigue development during rhythmic movement execution, finger tapping (FT) at the maximal rate, and fatigue after effects on the stability of rhythmic patterns. Participants (n = 19) performed six sets of unresisted FT (with a 3 min rest in‐between). Each set included four interleaved 30 s repetitions of self‐selected (two repetitions) and maximal rate FT (two repetitions) without rest in‐between. Left DLPFC involvement in the task was perturbed by transcranial static magnetic stimulation (tSMS) in two sessions (one real and one sham). Moreover, half of the self‐selected FT repetitions were performed concurrently with a demanding cognitive task, the Stroop test. Compared with sham stimulation, real tSMS stimulation prevented waning in tapping frequency at the maximal rate without affecting perceived levels of fatigue. Participants' engagement in the Stroop test just prior to maximal FT reduced the movement amplitude during this mode of execution. Movement variability at self‐selected rates increased during Stroop execution, especially under fatigue previously induced by maximal FT. Our results indicate cognitive‐motor interactions and a prominent role of the prefrontal cortex in fatigue and the motor control of simple repetitive movement patterns. We suggest the need to approach motor fatigue including cognitive perspectives.

We show the fundamental role of executive areas in fatigue caused by very simple repetitive movements. Fatigue developed less during the maximal frequency of movement production, while the left DLPFC received magnetic stimulation (in right‐handers). The role of cognitive‐motor interaction in fine motor control was also clear when participants engaged in cognitive tasks. At the clinical level, our work reinforces the need to treat fatigue from a comprehensive perspective.

Event-related potentials evoked by skin puncture reflect activation of Aβ fibers: comparison with intraepidermal and transcutaneous electrical stimulations

Background

Recently, event-related potentials (ERPs) evoked by skin puncture, commonly used for blood sampling, have received attention as a pain assessment tool in neonates. However, their latency appears to be far shorter than the latency of ERPs evoked by intraepidermal electrical stimulation (IES), which selectively activates nociceptive Aδ and C fibers. To clarify this important issue, we examined whether ERPs evoked by skin puncture appropriately reflect central nociceptive processing, as is the case with IES.

Methods

In Experiment 1, we recorded evoked potentials to the click sound produced by a lance device (click-only), lance stimulation with the click sound (click+lance), or lance stimulation with white noise (WN+lance) in eight healthy adults to investigate the effect of the click sound on the ERP evoked by skin puncture. In Experiment 2, we tested 18 heathy adults and recorded evoked potentials to shallow lance stimulation (SL) with a blade that did not reach the dermis (0.1 mm insertion depth); normal lance stimulation (CL) (1 mm depth); transcutaneous electrical stimulation (ES), which mainly activates Aβ fibers; and IES, which selectively activates Aδ fibers when low stimulation current intensities are applied. White noise was continuously presented during the experiments. The stimulations were applied to the hand dorsum. In the SL, the lance device did not touch the skin and the blade was inserted to a depth of 0.1 mm into the epidermis, where the free nerve endings of Aδ fibers are located, which minimized the tactile sensation caused by the device touching the skin and the activation of Aβ fibers by the blade reaching the dermis. In the CL, as in clinical use, the lance device touched the skin and the blade reached a depth of 1 mm from the skin surface, i.e., the depth of the dermis at which the Aβ fibers are located.

Results

The ERP N2 latencies for click-only (122 ± 2.9 ms) and click+lance (121 ± 6.5 ms) were significantly shorter than that for WN+lance (154 ± 7.1 ms). The ERP P2 latency for click-only (191 ± 11.3 ms) was significantly shorter than those for click+lance (249 ± 18.6 ms) and WN+lance (253 ± 11.2 ms). This suggests that the click sound shortens the N2 latency of the ERP evoked by skin puncture. The ERP N2 latencies for SL, CL, ES, and IES were 146 ± 8.3, 149 ± 9.9, 148 ± 13.1, and 197 ± 21.2 ms, respectively. The ERP P2 latencies were 250 ± 18.2, 251 ± 14.1, 237 ± 26.3, and 294 ± 30.0 ms, respectively. The ERP latency for SL was significantly shorter than that for IES and was similar to that for ES. This suggests that the penetration force generated by the blade of the lance device activates the Aβ fibers, consequently shortening the ERP latency.

Conclusions

Lance ERP may reflect the activation of Aβ fibers rather than Aδ fibers. A pain index that correctly and reliably reflects nociceptive processing must be developed to improve pain assessment and management in neonates.

Transient Modulation of Working Memory Performance and Event-Related Potentials by Transcranial Static Magnetic Field Stimulation over the Dorsolateral Prefrontal Cortex

Transcranial static magnetic field stimulation (tSMS) can modulate human cortical excitability and behavior. To better understand the neuromodulatory effect of tSMS, this study investigates whether tSMS applied over the left dorsolateral prefrontal cortex (DLPFC) modulates working memory (WM) performance and its associated event-related potentials (ERPs). Thirteen healthy participants received tSMS or sham stimulation over the left DLPFC for 26 min on different days. The participants performed a 2-back version of the n-back task before, during (20 min after the start of stimulation), immediately after, and 15 min after the stimulation. We examine reaction time for correct responses, d-prime reflecting WM performance, and the N2 and P3 components of ERPs. Our results show that there was no effect of tSMS on reaction time. The d-prime was reduced, and the N2 latency was prolonged immediately after tSMS. These findings indicate that tSMS over the left DLPFC affects WM performance and its associated electrophysiological signals, which can be considered an important step toward a greater understanding of tSMS and its use in studies of higher-order cognitive processes.

Null Effect of Transcranial Static Magnetic Field Stimulation over the Dorsolateral Prefrontal Cortex on Behavioral Performance in a Go/NoGo Task

The purpose of this pilot study was to investigate whether transcranial static magnetic field stimulation (tSMS), which can modulate cortical excitability, would influence inhibitory control function when applied over the dorsolateral prefrontal cortex (DLPFC). Young healthy adults (n = 8, mean age ± SD = 24.4 ± 4.1, six females) received the following stimulations for 30 min on different days: (1) tSMS over the left DLPFC, (2) tSMS over the right DLPFC, and (3) sham stimulation over either the left or right DLPFC. The participants performed a Go/NoGo task before, immediately after, and 10 min after the stimulation. They were instructed to extend the right wrist in response to target stimuli. We recorded the electromyogram from the right wrist extensor muscles and analyzed erroneous responses (false alarm and missed target detection) and reaction times. As a result, 50% of the participants made erroneous responses, and there were five erroneous responses in total (0.003%). A series of statistical analyses revealed that tSMS did not affect the reaction time. These preliminary findings suggest the possibility that tSMS over the DLPFC is incapable of modulating inhibitory control and/or that the cognitive load imposed in this study was insufficient to detect the effect.

Static magnetic stimulation in the central nervous system: a systematic review

OBJECTIVE

To systematically review the literature on the use of the transcranial static magnetic stimulation (tSMS) technique in humans and animals, its effects on different areas of the central nervous system (CNS), its influence on neural excitability and on the subject's behavior, and its biological effects and future possibilities. All static magnetic field applications that can be considered to have a physiologically similar effect have been reviewed.

METHODS

We searched studies using key terms in NCBI PubMed, Scopus, PEDro, SciELO, Cochrane, and links to publications (inception to September 2019). Three reviewers independently selected the studies, extracted data, and assessed the methodological quality of the studies using the recommendations described in the Cochrane Handbook for Systematic Reviews of Interventions, PRISMA guidelines.

RESULTS

We analyzed 27 studies. The reviewed literature suggests that the use of these magnetic fields has an inhibitory effect on different areas of the CNS, such as motor, somatosensory, and visual cortex, cerebellum, and spinal cord. Regarding subject's behavior, the different effects of tSMS appear to be transient and dependent on the stimulated area, such as loss of visual discrimination or improvement of somatosensory perception. In addition, the technique has some therapeutic utility, specifically in pathologies with cortical hyperexcitability.

CONCLUSIONS

These results suggest that tSMS may be a promising tool to modulate cerebral excitability in a safe and non-invasive way. Further investigations could give a better explanation of its precise mechanisms of action and applications.

Can Event-Related Potentials Evoked by Heel Lance Assess Pain Processing in Neonates? A Systematic Review

To clarify the possibility of event-related potential (ERP) evoked by heel lance in neonates as an index of pain assessment, knowledge acquired by and problems of the methods used in studies on ERP evoked by heel lance in neonates were systematically reviewed, including knowledge about Aδ and C fibers responding to noxious stimuli and Aβ fibers responding to non-noxious stimuli. Of the 863 reports searched, 19 were selected for the final analysis. The following points were identified as problems for ERP evoked by heel lance in neonates to serve as a pain assessment index: (1) It is possible that the ERP evoked by heel lance reflected the activation of Aβ fibers responding to non-noxious stimuli and not the activation of Aδ or C fibers responding to noxious stimulation; (2) Sample size calculation was presented in few studies, and the number of stimulation trials to obtain an averaged ERP was small. Accordingly, to establish ERP evoked by heel lance as a pain assessment in neonates, it is necessary to perform a study to clarify ERP evoked by Aδ- and C-fiber stimulations accompanied by heel lance in neonates.

Safety and recommendations for TMS use in healthy subjects and patient populations, with updates on training, ethical and regulatory issues: Expert Guidelines

This article is based on a consensus conference, promoted and supported by the International Federation of Clinical Neurophysiology (IFCN), which took place in Siena (Italy) in October 2018. The meeting intended to update the ten-year-old safety guidelines for the application of transcranial magnetic stimulation (TMS) in research and clinical settings (Rossi et al., 2009). Therefore, only emerging and new issues are covered in detail, leaving still valid the 2009 recommendations regarding the description of conventional or patterned TMS protocols, the screening of subjects/patients, the need of neurophysiological monitoring for new protocols, the utilization of reference thresholds of stimulation, the managing of seizures and the list of minor side effects. New issues discussed in detail from the meeting up to April 2020 are safety issues of recently developed stimulation devices and pulse configurations; duties and responsibility of device makers; novel scenarios of TMS applications such as in the neuroimaging context or imaging-guided and robot-guided TMS; TMS interleaved with transcranial electrical stimulation; safety during paired associative stimulation interventions; and risks of using TMS to induce therapeutic seizures (magnetic seizure therapy). An update on the possible induction of seizures, theoretically the most serious risk of TMS, is provided. It has become apparent that such a risk is low, even in patients taking drugs acting on the central nervous system, at least with the use of traditional stimulation parameters and focal coils for which large data sets are available. Finally, new operational guidelines are provided for safety in planning future trials based on traditional and patterned TMS protocols, as well as a summary of the minimal training requirements for operators, and a note on ethics of neuroenhancement.

Influence of Static Magnetic Field Stimulation on the Accuracy of Tachystoscopically Presented Line Bisection

Transcranial static magnetic stimulation (tSMS) has been known to reduce human cortical excitability. Here, we investigated whether tSMS would modulate visuo-spatial cognition in healthy humans. Subjects performed a visuo-spatial task requiring judgements about the symmetry of pre-bisected lines. Visual stimuli consisted of symmetrically or asymmetrically transected lines, tachystoscopically presented for 150 ms on a computer monitor. Task performance was examined before, immediately after, and 10 min after tSMS/sham stimulation of 20 min over the posterior parietal cortex (PPC: P4 from the international 10-20 system) or superior temporal gyrus (STG: C6). Nine out of 16 subjects misjudged pre-bisected lines by consistently underestimating the length of the right-side segment (judging lines to be exactly pre-bisected when the transector was located to the left of the midpoint, or judging the left-side segment to be longer when the transector was located at the midpoint). In these subjects showing a leftward bias, tSMS over the right STG reduced the magnitude of the leftward bias. This did not occur with tSMS over the right PPC or sham stimulation. In the remaining right-biased subjects, no intervention effect was observed with any stimulation. Our findings indicate that application of tSMS over the right STG modulates visuo-spatial cognition in healthy adults.

A Systematic Review of the Effectiveness of Non-Invasive Brain Stimulation Techniques to Reduce Violence Proneness by Interfering in Anger and Irritability

The field of neurocriminology has proposed several treatments (e.g., pharmacological, brain surgery, androgen-deprivation therapy, neurofeedback) to reduce violence proneness, but unfortunately, their effectiveness has been limited due to their side-effects. Therefore, it is necessary to explore alternative techniques to improve patients’ behavioural regulation with minimal undesirable effects. In this regard, non-invasive brain stimulation techniques, which are based on applying changing magnetic fields or electric currents to interfere with cortical excitability, have revealed their usefulness in alleviating the symptomatology of several mental disorders. However, to our knowledge, there are no reviews that assess whether these techniques are useful for reducing violence proneness. Therefore, we conducted a systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria using the following databases: PsycINFO, PubMed, Dialnet, Psicodoc, Web of Knowledge, and the Cochrane Library. We initially identified 3746 entries, and eventually included 56 publications. Most of the studies were unanimous in concluding that the application of these techniques over the prefrontal cortex (PFC) was not sufficient to promote anger and irritability reductions in euthymic individuals of both genders. Nevertheless, the application of non-invasive brain stimulation techniques, especially transcranial direct current stimulation, over the right PFC seemed to reduce violent reactions in these individuals by interfering with the interpretation of the unfavourable situations (e.g., threating signals) or inner states that evoked anger. In antisocial and pathological populations, the conclusions were provided by a few pilot studies with important methodological weaknesses. The main conclusion of these studies was that bilateral stimulation of the PFC satisfactorily reduced anger and irritability only in inmates, patients with autism spectrum disorders (ASD), people who suffered a closed-head injury, and agitated patients with Alzheimer’s disease. Moreover, combining these techniques with risperidone considerably reduced aggressiveness in these patients. Therefore, it is necessary to be cautious about the benefits of these techniques to control anger, due the methodological weaknesses of these studies. Nonetheless, they offer valuable opportunities to prevent violence by designing new treatments combining brain stimulation with current strategies, such as psychotherapy and psychopharmacology, in order to promote lasting changes.

Static magnetic field stimulation of the supplementary motor area modulates resting-state activity and motor behavior

Focal application of a strong static magnetic field over the human scalp induces measurable local changes in brain function. Whether it also induces distant effects across the brain and how these local and distant effects collectively affect motor behavior remains unclear. Here we applied transcranial static magnetic field stimulation (tSMS) over the supplementary motor area (SMA) in healthy subjects. At a behavioral level, tSMS increased the time to initiate movement while decreasing errors in choice reaction-time tasks. At a functional level, tSMS increased SMA resting-state fMRI activity and bilateral functional connectivity between the SMA and both the paracentral lobule and the lateral frontotemporal cortex, including the inferior frontal gyrus. These results suggest that tSMS over the SMA can induce behavioral aftereffects associated with modulation of both local and distant functionally-connected cortical circuits involved in the control of speed-accuracy tradeoffs, thus offering a promising protocol for cognitive and clinical research.

Transcranial Static Magnetic Field Stimulation Over the Temporal Cortex Modulating the Right Ear Advantage in Dichotic Listening

OBJECTIVE

Transcranial static magnetic field stimulation (tSMS) has proposed a new, promising, and simple non-invasive brain stimulation method. While several studies gained certain evidence about tSMS effects in the motor, somatosensory, and visual domains, there is still a controversial debate about its general effectiveness. In the present study, we investigated potential tSMS effects on auditory speech processing as measured by a dichotic listening (DL) task.

MATERIALS AND METHODS

Fifteen healthy participants received in randomized order on three different days one session of either sham, tSMS over the left, or tSMS over the right auditory cortex (AC). Under stimulation, participants performed a standard DL task with consonant-vowel syllables. Simultaneously, we recorded electroencephalogram from central sites (Fz, Cz, Pz).

RESULTS

TSMS over the left AC changed the behavioral performance and modulated auditory evoked potentials. Stimulation of the left AC significantly reduced the right ear advantage during the DL task and the N1 component of auditory evoked potentials in response to these syllables.

CONCLUSIONS

The preliminary results of the present exploratory study demonstrate the ability of tSMS to modulate human brain activity on a behavioral as well as physiologic level. Furthermore, tSMS effects on acoustic processing may have clinical implications by fostering potential approaches for a treatment of speech-related pathologies associated with hyperexcitability in the AC.

Exercise and movement in musculoskeletal pain: a double-edged problem

PURPOSE OF REVIEW

Exercise and movement are increasingly used in pain management and in palliative care, outside the traditional context of physical medicine and rehabilitation. This critical review aims to provide specialists in pain and palliative medicine with recent insights into the use of exercise and movement in the approach to musculoskeletal disorders when pain and disability are the major complaints.

RECENT FINDINGS

If there is a common sense linking pain and movement in both directions, that is pain influencing movement - as a withdrawal movement or a reduction of mobility as a defense reaction - or movement evoking pain, not so clear and recognized is the link between exercise and movement in controlling pain.

SUMMARY

Conflicting results emerge between absolutely convincing basic science research confirming important effects induced by movement and exercise on pain and substantial poor low evidence level from clinical research as stated by almost all systematic reviews. The need of rigorous clinical trials is mandatory to ascertain a real clinical benefit for the use of movement and exercise for pain control.

Clinical neurophysiology of pain

Clinical neurophysiologic investigation of pain pathways in humans is based on specific techniques and approaches, since conventional methods of nerve conduction studies and somatosensory evoked potentials do not explore these pathways. The proposed techniques use various types of painful stimuli (thermal, laser, mechanical, or electrical) and various types of assessments (measurement of sensory thresholds, study of nerve fiber excitability, or recording of electromyographic reflexes or cortical potentials). The two main tests used in clinical practice are quantitative sensory testing and pain-related evoked potentials (PREPs). In particular, PREPs offer the possibility of an objective assessment of nociceptive pathways. Three types of PREPs can be distinguished depending on the type of stimulation used to evoke pain: laser-evoked potentials, contact heat evoked potentials, and intraepidermal electrical stimulation evoked potentials (IEEPs). These three techniques investigate both small-diameter peripheral nociceptive afferents (mainly Aδ nerve fibers) and spinothalamic tracts without theoretically being able to differentiate the level of lesion in the case of abnormal results. In routine clinical practice, PREP recording is a reliable method of investigation for objectifying the existence of a peripheral or central lesion or loss of function concerning the nociceptive pathways, but not the existence of pain. Other methods, such as nerve fiber excitability studies using microneurography, more directly reflect the activities of nociceptive axons in response to provoked pain, but without detecting or quantifying the presence of spontaneous pain. These methods are more often used in research or experimental study design. Thus, it should be kept in mind that most of the results of neurophysiologic investigation performed in clinical practice assess small fiber or spinothalamic tract lesions rather than the neuronal mechanisms directly at the origin of pain and they do not provide objective quantification of pain.