Effects of Paired-pulse Transcranial Magnetic Stimulation of the Motor Cortex on Perception of Experimentally Induced Pain

Modulation of the nociceptive flexion reflex by conservative therapy in patients and healthy people: a systematic review and meta-analysis

ABSTRACT

The nociceptive flexion reflex (NFR) is a spinally mediated withdrawal response and is used as an electrophysiological marker of descending modulation of spinal nociception. Chemical and pharmacological modulation of nociceptive neurotransmission at the spinal level has been evidenced by direct effects of neurotransmitters and pharmacological agents on the NFR. Largely unexplored are, however, the effects of nonpharmacological noninvasive conservative interventions on the NFR. Therefore, a systematic review and meta-analysis was performed and reported following the PRISMA guidelines to determine whether and to what extent spinal nociception measured through the assessment of the NFR is modulated by conservative therapy in patients and healthy individuals. Five electronic databases were searched to identify relevant articles. Retrieved articles were screened on eligibility using the predefined inclusion criteria. Risk of bias was investigated according to Version 2 of the Cochrane risk-of-bias assessment tool for randomized trials. The evidence synthesis for this review was conducted in accordance with the Grading of Recommendations Assessment, Development and Evaluation. Thirty-six articles were included. Meta-analyses provided low-quality evidence showing that conservative therapy decreases NFR area and NFR magnitude and moderate-quality evidence for increases in NFR latency. This suggests that conservative interventions can exert immediate central effects by activating descending inhibitory pathways to reduce spinal nociception. Such interventions may help prevent and treat chronic pain characterized by enhanced spinal nociception. Furthermore, given the responsiveness of the NFR to conservative interventions, the NFR assessment seems to be an appropriate tool in empirical evaluations of treatment strategies.PROSPERO registration number: CRD42020164495.

The "virtual lesion" approach to transcranial magnetic stimulation: studying the brain-behavioral relationships in experimental pain

Transcranial magnetic stimulation (TMS) can be used to create a temporary “virtual lesion” (VL) of a target cortical area, disrupting its function and associated behavior. Transcranial magnetic stimulation can therefore test the functional role of specific brain areas. This scoping review aims at investigating the current literature of the “online” TMS-evoked VL approach to studying brain–behavioral relationships during experimental pain in healthy subjects. Ovid-Medline, Embase, and Web of Science electronic databases were searched. Included studies tested different TMS-based VLs of various pain brain areas during continuous experimental pain or when time-locked to a noxious stimulus. Outcome measures assessed different pain measurements. Initial screening resulted in a total of 403 studies, of which 17 studies were included in the review. The VLs were directed to the prefrontal, primary and secondary somatosensory, primary motor, and parietal cortices through single/double/triple/sequence of five-TMS pulses or through repeated TMS during mechanical, electrical contact, radiant heat, or capsaicin-evoked noxious stimulation. Despite a wide variability among the VL protocols, outcome measures, and study designs, a behavioral VL effect (decrease or increase in pain responses) was achieved in the majority of the studies. However, such findings on the relationships between the modified brain activity and the manifested pain characteristics were often mixed. To conclude, TMS–elicited VLs during experimental pain empower our understanding of brain–behavior relationships at specific time points during pain processing. The mixed findings of these relationships call for an obligatory standard of all pain-related TMS protocols for clearly determining the magnitude and direction of TMS-induced behavioral effects.

Repetitive transcranial magnetic stimulation in chronic pain: a review of the literature

OBJECTIVE

To review the literature on the analgesic effects of repetitive transcranial magnetic stimulation (rTMS) in chronic pain according to different pain syndromes and stimulation parameters.

DATA SOURCES

Publications on rTMS and chronic pain were searched in PubMed and Google Scholar using the following key words: chronic pain, analgesia, transcranial magnetic stimulation, neuropathic pain, fibromyalgia, and complex regional pain syndrome.

STUDY SELECTION

This review only included double-blind, controlled studies with >10 participants in each arm that were published from 1996 to 2014 and written in English. Studies with relevant information for the understanding of the effects of rTMS were also cited.

DATA EXTRACTION

The following data were retained: type of pain syndrome, type of study, coil type, target, stimulation intensity, frequency, number of pulses, orientation of induced current, number of session, and a brief summary of intervention outcomes.

DATA SYNTHESIS

A total of 33 randomized trials were found. Many studies reported significant pain relief by rTMS, especially high-frequency stimulation over the primary motor cortex performed in consecutive treatment sessions. Pain relief was frequently >30% compared with control treatment. Neuropathic pain, fibromyalgia, and complex regional pain syndrome were the pain syndromes more frequently studied. However, among all published studies, only a few performed repetitive sessions of rTMS.

CONCLUSIONS

rTMS has potential utility in the management of chronic pain; however, studies using maintenance sessions of rTMS and assessing the effects of rTMS on the different aspects of chronic pain are needed to provide a more solid basis for its clinical application for pain relief.