Pain and consciousness: a TMS/EEG study

In the present research we investigated pain perception mechanisms through transcranial magnetic stimulation (rTMS), studying the effect of rTMS (10-minutes 5 Hz applied to left dorsolateral prefrontal cortex, DLPFC) on acute pain experience. A sample of healthy participants took part to the study. We used a capsaicin-based gel to induce acute but progressive experimentally-controlled pain and recorded self-report Visual-Analogue Scales (VAS) for pain intensity each 5 minutes and EEG measures over time. The experimental design included five 5-minutes recording blocks: a pre- rTMS stimulation baseline and four consecutive post-stimulation blocks. The capsaicin gel was applied to the back of the non-dominant hand at the beginning of the first post-stimulation recording block and removed at the beginning of the last one. The results showed a greater frontal cortical activation involving Theta frequency increasing after rTMS stimulation. These data were supported by VAS scores that showed increased values and a long-lasting time perception after capsaicin gel application compared to subjects who did not receive rTMS stimulation. DLPFC is usually related to sustaining attention, conscious monitoring and control function. We supposed, compared with previous research, that these results may represent a significant modulation effect on the monitoring and control experiences, pain-related, after 5Hz rTMS applied on the left DLPFC. The use of TMS paradigm may suggest a relevant role of DLPFC in monitoring and inhibition processes in pain experience, maybe related to a greater consciousness of pain. Nonetheless, they may hint at clinical interventions to relieve pain in chronic patients where non-invasive techniques may complement pharmacological treatment.