Neural correlates of sustained deep-tissue pain: an EEG study

J. M. VÖLKER; F. G. ARGUISSAIN; J. A. BIURRUN MANRESA; O. K. ANDERSEN

Boston

Congreso; 17th World Congress on Pain; 2018

IASP

Aim of Investigations: The aim of this work was to characterize the source-localized cortical activity and brain connectivity during deep tonic painful cuff stimulation using CPA, specifically in the salience network. It was hypothesized that deep tonic painful stimulation increases cortical activity and functional connectivity of the salience network in beta and gamma band and decreases in alpha band. Methods: 20 healthy subjects (6 males and 14 females, age 24.5 ± 2.5) were recruited for the experiment. Electroencephalography (EEG) was recorded from 64 channels during rest and painful stimulation with the cuff over the right forearm. Three minutes of artefact-free EEG data was selected to assess the cortical source generators of alpha (8-12 Hz), beta (12-30 Hz), and gamma (30-70 Hz) frequency bands by means of the exact low-resolution brain electromagnetic tomography source localization (LORETA). Furthermore, functional connectivity metrics (lagged phase synchronization and lagged coherence) were calculated in 11 regions of interest that correspond to the salience network. Cortical source activity and functional connectivity were compared between conditions trough t-statistic on logarithm-transformed data. Results: Tonic deep painful stimulation decreased cortical activity in the alpha band in the right insula (T = -5.21, p < 0.01), contralateral primary somatosensory cortex (T = -4.36, p < 0.05), and left inferior frontal gyrus (T= -4.59, p < 0.05) when compared to rest. Furthermore, functional connectivity analysis showed that during tonic painful stimulation there was decreased lagged coherence in the alpha band between the left insula and left supramarginal gyrus (T = 2.96, p < 0.05). Moreover, tonic deep painful stimulation increased lagged coherence in the gamma band between the right insula and right supramarginal gyrus (T=3.19, p < 0.05) and between the right insula and the right orbito frontal gyrus (T = 2.70, p < 0.05). No statistical differences were found in lagged phase synchronization. Conclusions: Overall findings indicate that deep tonic painful stimulation using CPA significantly decreases alpha brain activity and connectivity within the salience network. In other words, the alpha synchrony, which is generally associated with an idle state, was lower during deep tonic pain than during rest. This possibly reflects release of inhibition. This shift facilitates the alerting function of pain. Functional connectivity analysis showed an increased coherence within the salience network in the gamma band, particularly in the right insula which is a central hub in salience detection. Similar results have been previously shown during tonic stimulation of superficial skin receptors using cold pressure test and heat stimuli.