Computation of Brain Activity Changes After a Transcranial Direct Current Stimulation Therapy for Neuropathic Pain in Spinal Cord Injury

Abstract

Neuropathic pain is a condition that affects over 53% of patients that have a spinal cord injury (SCI). On the other hand, transcranial direct current stimulation (tDCS) is a technique that applies a constant current across two electrodes placed over the scalp modulating brain activity. tDCS could aid in the treatment of neuropathic pain of SCI patients, however, its neurophysiological effects are scarcely reported. In this work, electroencephalography (EEG) derived features were computed before and after tDCS was applied to SCI patients with neuropathic pain, with the hypothesis that significant pre-therapy to post-therapy differences would be observed in frontocentral regions. EEG data was analyzed comprising information from eight patients that received 14 sessions of tDCS therapy as part of an ongoing study at the Instituto Nacional de Rehabilitación Luis Guillermo Ibarra Ibarra. EEG extracted features comprised theta and alpha power computed with the taper method using a Hanning window, during two conditions, a resting state with eyes opened and a resting state with eyes closed. Alpha reactivity was also computed from alpha power during these conditions. Statistical tests showed that theta power during eyes opened in FC4 was the only channel where significant pre-therapy to post-therapy differences could be observed. A post-hoc power analysis implied that a larger sample would be needed to assess if these absences of significant differences are due to tDCS not eliciting them, or due to the small sample size. Statistical power analysis implied that samples of 43 to hundreds of patients would be needed to correctly assess neurophysiological differences in theta and alpha EEG features after a tDCS intervention in SCI targeting neuropathic pain.