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

Abstract

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 motorcortex 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.Key Words: motor control, motor cortex, pain, plasticity, rehabilitation RÉ SUMÉObjectif : La douleur est considé rablement invalidante et pré sente souvent des interactions avec d'autres dé ficits au cours du processus de ré adaptation. L'objectif de cet article est d'analyser donné e supportant la pré sence d'interactions entre la douleur et le cortex moteur afin de tenter de ré pondre aux questions suivantes : (1) La douleur aiguë nuit-elle à l'activité du cortex moteur? (2) La douleur chronique altè re-t-elle l'activité du cortex moteur et, ré ciproquement, la ré organisation du cortex moteur contribue-t-elle à la douleur chronique? (3) L'induction de la plasticité motrice par stimulation du cortex moteur peut-elle ré duire la douleur? (4) L'entraînement moteur peut-il amener à la fois une ré organisation du cortex moteur et un soulagement de la douleur? Ré sumé des principaux points : Il a é té clairement dé montré que la douleur aiguë expé rimentale exerce une influence inhibitoire sur le cortex moteur, qui peut entraver les capacité s d'apprentissage moteur. Les donné e actuelles suggè rent é galement qu'il existe une relation entre la douleur chronique et la ré organisation du cortex moteur, mais il n'est pas clair que l'un provoque l'autre. Il existe toutefois des preuves de plus en plus nombreuses que les interventions visant à normaliser l'organisation du cortex peuvent amener un soulagement de la douleur. Conclusions : Les interactions entre la douleur et le cortex moteur sont complexes et d'autres é tudes sont né cessaires pour comprendre ces interactions chez nos patients et pour concevoir des straté gies de ré adaptation optimales.

Alterations in central motor representation increase over time in individuals with rotator cuff tendinopathy

“…Change in corticospinal excitability could be attributable to several causes. For example, patients with MSK disorders experienced pain for a prolonged period, and pain has been shown to exert an inhibitory effect over M1 (for reviews see (Farina et al, 2003;Mercier and Léonard, 2011;Bank et al, 2013)). It has recently been shown that even low pain levels are sufficient to induce such inhibition, and that the perceived pain level is not associated with the level of inhibition (Dubé and Mercier, 2011).…”

Immediate and Sustained Effects of 5-Day Transcranial Direct Current Stimulation of the Motor Cortex in Phantom Limb Pain

“…Moreover, a recent work has shown that a single session of anodal tDCS of the motor cortex results in an instant reduction of mu opioid receptor binding of an exogenous receptor ligand in the pain matrix (i.e., nucleus accumbens, anterior cingulate cortex, insula, thalamus), suggesting that the analgesic effect of M1-tDCS may possibly be due to a direct increase of endogenous opioid release [11]. The long-term analgesic effects of motor cortex stimulation could also follow, at least partially, the restoration of defective intracortical inhibitory processes, shown to be impaired following amputation [35].…”

“…Transcranial Magnetic Stimulation (TMS) studies in upper-and lower-limb amputees show that motor threshold and intracortical inhibition decreases for the muscle proximal to the amputation, suggesting an increased excitability of the corticospinal neurons and a reduction of GABA activity at the cortical level [7,9,10,30,47]. Although the relationship between motor excitability and PLP remains unclear [30,35], these cortical excitability shifts were shown to be larger in patients with PLP than in pain-free patients [13,24,30].…”

Effect of Tonic Pain on Motor Acquisition and Retention while Learning to Reach in a Force Field

“…It has been demonstrated that pain can lead to a reduction of maximal voluntary contraction, a decrease in endurance and changes in coordination during dynamic motor tasks (see [8]–[11] for reviews), although the cause of these alterations in motor function are still not fully understood. Several studies have also investigated the influence of pain on corticospinal excitability by looking at motor responses evoked by transcranial magnetic stimulation (TMS) applied over M1 [11]–[13]. Most of these studies reported that different types of acute experimental pain applied within or close to the target muscle exert an inhibitory influence on corticospinal excitability [14]–[26].…”