Personality and placebo analgesia during cold stimulation in women: A Low-Resolution Brain Electromagnetic Tomography (LORETA) analysis of startle ERPs

We applied exact low-resolution brain electromagnetic tomography (eLORETA) method to auditory startle event-related potentials (ERPs) during cold pain (cold-cup-test: CCT). ERPs and startle data were obtained from a published dataset wherein auditory startle stimuli were used as probes of pain processing (De Pascalis & Scacchia, 2016). We wanted to identify (1) sources of cortical current density changes associated with pain/distress reductions to placebo analgesia (PA) treatment, and (2) sources of activity changes that are predictors of the behavioural inhibition system (BIS) and fight/flight/freeze system (FFFS) of the revised Reinforcement Sensitivity Theory (rRST). We administered three treatments: Baseline, CCT-alone (Pain), and CCT plus sham cream (Placebo). PA, as compared to Pain treatment, was effective in pain and distress reduction, and produced a significant current density reduction within right primary somatosensory cortex (S1) and left middle frontal gyrus (MFG). In addition, current density change in the right S1 was a positive predictor of subjective pain and distress reduction, although distress reduction was also associated with decreased activity in the left MFG. We failed to identify regional sources of placebo-related current density changes as predictors of the BIS and FFFS with the exception of current density changes within left MFG that was positively correlated with BIS and a significant predictor of this trait. Findings appear consistent with rRST predictions suggesting BIS and FFFS as separate, but interacting neurobehavioural systems.