Martin Diers

Mirrored, imagined and executed movements differentially activate sensorimotor cortex in amputees with and without phantom limb pain

&NA; Extended viewing of movements of the intact hand in a mirror as well as motor imagery has been shown to decrease pain in phantom pain patients. We used functional magnetic resonance imaging to assess the neural correlates of mirrored, imagined and executed hand movements in 14 upper extremity amputees – 7 with phantom limb pain (PLP) and 7 without phantom limb pain (non‐PLP) and 9 healthy controls (HC). Executed movement activated the contralateral sensorimotor area in all three groups but ipsilateral cortex was only activated in the non‐PLP and HC group. Mirrored movements activated the sensorimotor cortex contralateral to the hand seen in the mirror in the non‐PLP and the HC but not in the PLP. Imagined movement activated the supplementary motor area in all groups and the contralateral primary sensorimotor cortex in the non‐PLP and HC but not in the PLP. Mirror‐ and movement‐related activation in the bilateral sensorimotor cortex in the mirror movement condition and activation in the sensorimotor cortex ipsilateral to the moved hand in the executed movement condition were significantly negatively correlated with the magnitude of phantom limb pain in the amputee group. Further research must identify the causal mechanisms related to mirror treatment, imagined movements or movements of the other hand and associated changes in pain perception.

Mirror therapy for phantom limb pain: Brain changes and the role of body representation

Phantom limb pain (PLP) is a common consequence of amputation and is difficult to treat. Mirror therapy (MT), a procedure utilizing the visual recreation of movement of a lost limb by moving the intact limb in front of a mirror, has been shown to be effective in reducing PLP. However, the neural correlates of this effect are not known.

Peripheral and electrocortical responses to painful and non-painful stimulation in chronic pain patients, tension headache patients and healthy controls ☆

Sixteen chronic back pain (CBP) patients, 16 tension headache (THA) patients and 16 healthy controls (HC) were exposed to four series of ten electric stimuli at perception threshold, pain threshold and 10% below pain tolerance. The EEG was recorded from three sites, in addition, the EMG from the m. frontalis and m. erector spinae, heart rate and skin conductance were assessed. The CBP patients showed significantly lower pain threshold and pain tolerance values than the HC and the THA patients whereas the THA patients displayed a higher pain tolerance. Habituation was reduced in the CBP group. N150, P260, P300 and N500 were not significantly different between the groups nor were there significant group differences in the peripheral measures. However, since the stimulation intensity was significantly lower in the CBP patients, these data are indicative of both enhanced central and peripheral reactivity. The observed lack of habituation may contribute to the persistence of chronic pain.

Sensorimotor training and cortical reorganization

Several disorders that involve motor and sensory disturbances such as chronic pain, tinnitus, stroke or dystonia are also characterized by changes in the sensory and motor maps in the sensorimotor cortices. This article reviews training procedures that target these maladaptive changes and the behavioral and cortical changes that accompany them. In addition, we will discuss factors that influence these training procedures and discuss new developments. These procedures include training of perceptual abilities, motor function, direct cortical stimulation as well as behavioral approaches and have been shown to reorganize the altered sensory and motor maps. Treatments that combine several modalities such as imagery or mirror treatment as well as use of prostheses also have beneficial effects. Further research must elucidate the mechanisms of these plastic changes and relate them to disorders and treatments.

Brain correlates of stress-induced analgesia

&NA; Stress‐induced analgesia (SIA) refers to a reduced pain response after stress exposure, which is mediated by descending pain‐inhibitory circuits and may be an indicator of adequate centrally mediated pain control. We used functional magnetic resonance imaging to assess brain mechanisms of SIA in 21 healthy participants. Using a block design series of mildly painful pressure stimuli were applied to the left medial phalanx of the second digit during functional magnetic resonance imaging. Mental arithmetic combined with increasing levels of noise was used as a stressor. Verbal ratings, changes in blood pressure and heart rate confirmed the validity of the stress induction. Post‐stress pain thresholds and pain tolerance were significantly higher and post‐stress pain and unpleasantness ratings were significantly lower compared to pre‐stress levels. SIA led to an increase of the blood‐level‐dependent oxygenation response in the primary somatosensory cortex, bilaterally in the anterior insula, and secondary somatosensory cortex. The increase in pain tolerance correlated significantly with activation in the rostral anterior cingulate cortex and pain unpleasantness with activation in the dorsal anterior cingulate cortex. SIA seems to activate similar brain networks as placebo analgesia or analgesia mediated by diffuse noxious inhibitory controls and involved sensory, affective and cognitive modulatory circuits.

Pain ratings and somatosensory evoked responses to repetitive intramuscular and intracutaneous stimulation in fibromyalgia syndrome.

Summary: To determine the presence of perceptual sensitization and related brain responses we examined 15 patients with fibromyalgia syndrome and 15 healthy controls comparable in age and sex. Multichannel EEG recordings and pain ratings were obtained during the presentation of 800 painful electrical intramuscular and intracutaneous stimuli to the left m. erector spinae and the left m. extensor digitorum. The stimulus intensity was adjusted to 50% between pain threshold and tolerance. Detection and pain thresholds were significantly lower in the fibromyalgia syndrome group. Sensitization occurred for both groups during intramuscular stimulation. In the EEG data the fibromyalgia syndrome patients showed higher N80 amplitudes compared with the healthy controls. Arm stimulation and intramuscular stimulation yielded higher N80 and N150 amplitudes compared with intracutaneous stimulation or stimulation of the back. These results indicate lower pain thresholds in the fibromyalgia syndrome patients after electrical stimulation and a higher N80 amplitude both indicative of enhanced sensory processing in this group.

The perceptual and neuronal stability of the rubber hand illusion across contexts and over time

The rubber hand illusion (RHI) offers the opportunity to systematically manipulate the experience of embodiment, which is here used to describe the subjective integration of an external object into ones body representation. Among the cortical regions involved in the processing of body perception, the ventral premotor cortex seems to be crucial in the integration of visuotactile stimuli. However, it is not known if the perceived vividness of the RHI is a trait or a state variable. In the present study, we varied the setup of the RHI to test the stability of perception. The illusion was induced in two different contexts, with either a horizontal or vertical displacement of the rubber hand in respect to the real hand. Further, the RHI was induced twice with an interval of at least six months and long-term changes on the perceptual and behavioral level were evaluated. Finally, we measured the long-term stability of cortical activity during the induction of a vertical RHI using functional magnetic resonance imaging. We found that a vertical setup induced higher ratings of illusory embodiment of the rubber hand than a horizontal setup, but the responses to both setups were significantly correlated. There was high intra-individual long-term stability of the subjective perception of illusory embodiment but a lower stability on the behavioral level. The functional magnetic resonance imaging data suggest temporally stable ventral premotor cortex processing. These results indicate that dynamic changes in perceived limb ownership by the induction of the RHI are trait-like.

The neural basis of phantom limb pain

A recent study suggests that brain changes in amputees may be pain-induced, questioning maladaptive plasticity as a neural basis of phantom pain. These findings add valuable information on cortical reorganization after amputation. We suggest further lines of research to clarify the mechanisms that underlie phantom pain.

Site-specific visual feedback reduces pain perception

&NA; Visual feedback of one’s own back reduces perceived pain intensity of nociceptive stimulation of the back in chronic back pain patients and in healthy controls. &NA; One of the most common forms of chronic pain is back pain. Until now, nothing has been known about the influence of visualizing one’s own back on pain perception at this site. We tested 18 patients with chronic back pain and 18 healthy controls, by implementing online video feedback of the back during painful pressure and subcutaneous electrical stimuli over the trapezius muscle. Pain threshold and pain tolerance were assessed. Pressure pain stimulation intensity was set to 50% above the pain threshold. Subcutaneous stimulation intensity was set to 70% above the pain threshold. Subjects had to rate pain intensity and unpleasantness after each stimulation block on an 11‐point numerical rating scale. Visual feedback of the back reduced perceived pain intensity compared to feedback of the hand in both patients and controls. These findings suggest novel intervention modes for chronic back pain based on visualization of body parts by augmented reality applications.

Recovery–stress balance and injury risk in professional football players: a prospective study

Abstract Professional football is a contact sport with a high risk of injury. This study was designed to examine the contribution of stress and recovery variables as assessed with the Recovery-Stress Questionnaire for Athletes (RESTQ-Sport) to the risk of injury in professional football players. In a prospective, non-experimental cohort design, 22 professional football players in the highest German football league were observed over the course of 16 months. From January 2010 until April 2011, the players completed the RESTQ-Sport a total of 222 times in monthly intervals. In addition, injury data were assessed by the medical staff of the club. Overall, 34 traumatic injuries and 10 overuse injuries occurred. Most of the injuries were located in the lower limb (79.5%), and muscle and tendon injuries (43.2%) were the most frequently occurring injury type. In a generalised linear model, the stress-related scales Fatigue (OR 1.70, P = 0.007), Disturbed Breaks (OR 1.84, P = 0.047) and Injury (OR 1.77, P < 0.001) and the recovery-related scale Sleep Quality (OR 0.53, P = 0.010) significantly predicted injuries in the month after the assessment. These results support the importance of frequent monitoring of recovery and stress parameters to lower the risk of injuries in professional football.