Not an Aspirin: No Evidence for Acute Anti-Nociception to Laser-Evoked Pain after Motor Cortex rTMS in Healthy Humans
2015
Brain Stimulation
Epub ahead of print
Authors: 
Bradley C
Perchet C
Lelekov-Boissard T
Magnin M
Garcia-Larrea L

Background: High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) has shown efficacy in relieving neuropathic pain. Whether its analgesic effect also applies to acute physiological nociception remains unclear due to previous contradictory findings.
Objective: To provide an in-depth investigation of the effects of motor cortex HF-rTMS on acute laserevoked pain and excitability of nociceptive networks in healthy subjects.
Methods: Randomized, placebo-controlled, double-blind, cross-over study in 20 healthy participants. Laser heat stimuli at nociceptive threshold were delivered to the right hand, allowing assessment of: (a) subjective pain intensity and unpleasantness; (b) laser-evoked potentials (LEPs, 128 electrodes) and their source model; (c) sympathetic skin responses, and (d) spino-thalamic pathway excitability. Data were collected before and 20 minutes after a session of neuro-navigated 20 Hz rTMS to the contralateral motor cortex.
Results: Subjective pain reports to thermal laser pulses, amplitude of late cortical potentials and sympathetic skin responses were decreased after cortical stimulation, to a similar extent whether it was active or placebo. Early cortical potentials and nociceptive network excitability remained identical before and after rTMS, as did anatomical sources of LEPs.
Conclusions: Our results do not provide evidence for a genuine anti-nociceptive effect of rTMS on acute physiological pain.We suggest that motor cortex rTMS may act upon high-order networks linked to the emotional and cognitive appraisal of chronic pain, and/or modulate pathologically sensitized networks, rather than change the physiological transmission within an intact nervous system. Such dichotomy is reminiscent of that observed with most drugs used for neuropathic pain