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Transcranial direct current stimulation of the primary motor cortex on postoperative pain and spontaneous oscillatory electroencephalographic activity following lumbar spine surgery: A pilot study.

BACKGROUND
Transcranial direct current stimulation (tDCS) on primary motor cortex (M1) provides a new way to relieve postoperative pain. Previous studies only found postoperative analgesia dosage significantly reduced in tDCS group while the patient-controlled analgesia (PCA) was applied. However, there lacks the study about the effect of M1-tDCS on pain intensity and brain activity while the analgesia dosage is the same for both groups.


OBJECTIVE
To investigate whether M1-tDCS can (1) reduce pain intensity and (2) change spontaneous electroencephalography (EEG) oscillations in prefrontal cortex, in patients with postoperative pain, after taking the constant dosage of analgesics.


METHODS
A prospective, single-blind, randomized, sham-controlled study was conducted. 32 patients with postoperative pain after lumbar spine surgery were recruited. All patients received same dosage of dezocine before intervention. In the morning of the first day after surgery and before dezocine injection, a single 20-minute session of anodal M1-tDCS was applied to 'tDCS' group while sham stimulation to 'sham' group. Numeric rating scale (NRS) and resting-state EEG with eyes-closed were measured and analyzed. EEG spectral powers were analyzed using repeated measures analysis of variance (ANOVA). Correlation analysis was conducted between the change of NRS and the change of spectral power.


RESULTS
The NRS in "tDCS" group significantly decreased (p < 0.01) while not in "sham" group after intervention. Only spectral power within alpha2 band (10-13 Hz) in Fp1 and beta1 band (13-20 Hz) in Fp1 showed significant Time×Intervention interaction effect. These changes of the spectral power also showed significant correlation with the change of NRS.


CONCLUSIONS
The postoperative pain intensity in patients receiving surgery could reduce after a single session of anodal M1-tDCS compared to sham M1-tDCS. The effect to the top-down dimension of postoperative pain might account for the analgesic effect of M1-tDCS, which reflecting slow oscillations in left prefrontal EEG.