Can a single pulse transcranial magnetic stimulation targeted to the motor cortex interrupt pain processing?

Lee-Bareket Kisler,Elliot Sprecher,Simone Shamay-Tsoory,Yelena Granovsky,Irit Weissman-Fogel,Alon Sinai,Ilan Gurion,Andrea Antal

doi:10.1371/journal.pone.0195739

Abstract

The modulatory role of the primary motor cortex (M1), reflected by an inhibitory effect of M1-stimulation on clinical pain, motivated us to deepen our understanding of M1’s role in pain modulation. We used Transcranial Magnetic Stimulation (TMS)-induced virtual lesion (VL) to interrupt with M1 activity during noxious heat pain. We hypothesized that TMS-VL will effect experimental pain ratings. Three VL protocols were applied consisting of single-pulse TMS to transiently interfere with right M1 activity: (1) VLM1- TMS applied to 11 subjects, 20 msec before the individual’s first pain-related M1 peak activation, as determined by source analysis (sLORETA), (2) VL-50 (N = 16; TMS applied 50 ms prior to noxious stimulus onset), and (3) VL+150 (N = 16; TMS applied 150 ms after noxious stimulus onset). Each protocol included 3 conditions ('pain-alone', ' TMS-VL', and ‘SHAM-VL’), each consisted of 30 noxious heat stimuli. Pain ratings were compared, in each protocol, for TMS-VL vs. SHAM-VL and vs. pain-alone conditions. Repeated measures analysis of variance, corrected for multiple comparisons revealed no significant differences in the pain ratings between the different conditions within each protocol. Therefore, our results from this exploratory study suggest that a single pulse TMS-induced VL that is targeted to M1 failed to interrupt experimental pain processing in the specific three stimulation timing examined here.

Highlights

Studies show that the primary motor cortex (M1) can modulate pain by influencing its affective or sensory components or by top down activation of the periaqueductal gray (PAG) [1,2,3,4,5,6]
We tried three different stimulation timing to interrupt M1 activity at different stages: (1) 50 msec prior to the noxious heat stimulation onset in order to interfere with M1 incoming activity, (2) 150 msec following the stimulus onset aiming at interfering with the M1 first peak activation, and (3) 20 msec before the individual M1 first peak activation for the purpose of impeding the ongoing M1 pain-related
We found that virtual lesion (VL) to M1 as applied in these three protocols, in our study has no effect on experimental pain intensity ratings

Summary

Introduction

Studies show that the primary motor cortex (M1) can modulate pain by influencing its affective or sensory components or by top down activation of the periaqueductal gray (PAG) [1,2,3,4,5,6]. Intracortical recordings [13] and functional neuro-imaging studies have reported pain-related changes in M1 activity [14, 15], in addition to activation of complex network of cerebral structures, associated with different dimensions of pain [16, 17]. If M1 is activated during pain process it does not mean that interruption of its activity will necessarily disrupt pain processing.

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Results

Conclusion