Repetitive transcranial magnetic stimulation over primary motor vs non-motor cortical targets; effects on experimental hyperalgesia in healthy subjects

Abstract

BackgroundHigh frequency repetitive transcranial magnetic stimulation (rTMS) targetted to different cortical regions (primary motor/sensory, prefrontal) are known to alter somatosensory responses. The mechanism(s) for these effects are unclear. We compared the analgesic effects of rTMS at different cortical sites on hyperalgesia induced using topical capsaicin cream.MethodsFourteen healthy subjects had capsaicin cream applied to a 16 cm2 area of the medial aspect of the right wrist (60 min) on 4 separate occasions over 6 weeks. rTMS (10Hz for 10s/min = 2000 stimuli @ 90% resting motor threshold of first dorsal interosseus muscle) was applied to the optimum site for right hand (M1), left dorsolateral prefrontal (DLFPC) and occipital midline (OCC) in a pseudo-randomised order. Thermal and mechanical perception and pain thresholds were determined using standardised quantitative sensory testing (QST) methods at the capsaicin site. Subjective responses to thermal stimuli (pain score on a numerical rating scale) from −2.5°C to +2.5°C of the individualised heat pain threshold (HPT) resulted in a hyperalgesia curve. Sensory testing took place prior to capsaicin application (PRE-CAP), after 30 min of capsaicin (POST-CAP) and following rTMS (30 min = POST-TMS).ResultsCapsaicin application resulted in substantial changes in thermal (but not mechanical) sensitivity to both heat and cold (eg. HPT PRE-CAP = 43.6°C to POST-CAP = 36.7°C (p < 0.001)) with no differences between groups pre-rTMS. POST-TMS HPT showed no changes for any of the treatment groups, however the pain scores for the hyperalgesia curve were significantly lower for M1 vs OCC (−24.7%, p < 0.001) and for M1 vs DLFPC (−18.3%, p < 0.02).ConclusionrTMS over the primary motor cortex results in a significant analgesic effect compared to other cortical areas.Electronic supplementary materialThe online version of this article (doi:10.1186/s12883-014-0166-3) contains supplementary material, which is available to authorized users.

Transcranial magnetic stimulation of the brain

“…However, pain processing is highly distributed throughout the brain. A small study recently demonstrated a trend towards reduction of acute pain after rTMS application to the occipital cortex, 104 and this approach was considered unacceptable in a recent systematic review. 58 Blinding TMS administrators is even more difficult and currently best addressed by coils that can be remotely programmed to deliver sham or true pulses, for instance, by opposing current flow within the loops to cancel their magnetic fields 46 or with a commercially available sham-capable system such as a MagVenture MagPro.…”

Neurostimulation Techniques for the Modulation of Pain

“…Multiple types of experimental pain have been used to study the effects of NIBS on nociceptive signaling in healthy human subjects [74]. tDCS of M1 produces sustained analgesia in chronic migraine, fibromyalgia, and orofacial pain [38].…”

Motor Cortex Reorganization and Repetitive Transcranial Magnetic Stimulation for Pain—A Methodological Study

“…Lack of a credible placebo coil hampers treatment blinding. We chose to use active stimulation over the occipital fissure for SHAM as it has been used in other studies with success and we believe to be preferable to coil rotation or tilt (2,40,68). To our knowledge, there have been no robust validation studies for the utility of "placebo" coils, although some studies appear to have used them successfully (42,69).…”

“…Experimental and clinical studies suggest that stimulation of primary motor cortex (M1) induces analgesia (1)(2)(3)(4)(5). Several controlled trials show that repetitive transcranial magnetic stimulation (rTMS) attenuates neuropathic pain, although the effect is modest and relatively short-lived (6)(7)(8)(9)(10).…”