P23.1 Using non-invasive brain stimulation to provoke modulatory effects on heat induced perception and pain threshold: application of a Bluetooth® interfaced stimulator

Introduction: Transcranial stimulation (magnetic and direct current) is able to change cortical excitability of the motor cortex. In case of chronic pain, modulatory effects have been demonstrated by using brain stimulation, and the mechanism is speculated to be plasticity changes. Objective: The aim of this study was to demonstrate the effect of transcranial direct current stimulation (tDCS) using a Bluetooth® controlled stimulator to modulate pain and perception thresholds to heat stimuli. Methods: In ten healthy controls anodal or sham tDCS was applied to the right primary motor cortex (M1) of the hand. We tested the threshold of heat induced perception and pain when applying heat to the cutaneous area of the superficial radial nerve of the contralateral and ipsilateral (control) hand. Furthermore, we tested cortical excitability using transcranial magnetic stimulation (TMS). Results: We found a significant threshold increase of heat induced perception (15%) and pain (5%) on the contralateral hand. There were no significant effects on the ipsilateral hand, nor for sham stimulation. The effect of tDCS applied for 10 min lasted for about 1 hour. By using TMS applied to the right M1, before and after 10 min of anodal tDCS, we found a significant increase of the motor evoked potentials (MEP) amplitude on the contralateral hand. When TMS was applied to the left M1, no significant changes were observed. Conclusions: The tDCS stimulator was able to modulate perception and pain thresholds, and might be a useful instrument for pain therapy. The effect of tDCS causes transitory brain plasticity and might be due to different mechanisms, such as increased cortical excitability, increased firing rate of neurons, physiological effect on the membrane resting potential, decreased muscle pain related to fatigue, or changes of the brain-derived neurotrophic factor (BDNF). However, further studies must be performed in order to understand the mechanisms of effect on chronic pain.