The Influence of Transcranial Direct Current Stimulation of the Motor Cortex on Balance in Parkinson's Disease
San Diego, CA
Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has been shown to improve motor performance of the upper limbs in Parkinson’s disease (PD). However, research is mixed on the ability of tDCS to improve lower limb motor function in gait and balance tasks, especially in tasks not done concurrently with tDCS (transfer tasks). Therefore, the purpose of this study was to determine the influence of tDCS applied during a gait training program on balance performance in PD. The study was a double-blind, sham-controlled, between-subjects experimental design. Twelve individuals with PD were allocated to either a tDCS group or a SHAM stimulation group. Each participant performed 9 training sessions over a 2 week period involving a gait training on an instrumented treadmill with online visual cues of stride length. In addition, anodal tDCS or SHAM was applied over the leg motor area of the motor cortex contralateral (dominant hemisphere) to the primarily affected leg. TDCS was applied at a current strength of 2 mA concurrently with the gait training for a duration of 20 minutes. SHAM stimulation was applied in the same manner according to well-established blinding procedures in which the current was ramped up and down over a 60 second period. Balance performance was assessed using computerized dynamic posturography of the Sensory Organization Test (SOT) in 4 testing sessions that occurred at baseline, the end of training (EOT), and at 2 (EOT+2) and 4 (EOT+4) weeks after training had ended. The primary outcome measures were the 6 equilibrium scores associated with the SOT along with the composite and 3 sensory system scores (somatosensory, visual, and vestibular). The primary outcome measures were analyzed with 2 Group (tDCS, SHAM) x 4 Testing Session (Baseline, EOT, EOT+2, EOT+4) repeated measures ANOVAs. For the somatosensory score, there was a significant Group x Testing Session interaction (P = 0.003), which indicated that somatosensory scores were higher for the tDCS group in the EOT testing session. However, post hoc analysis of the interaction just failed to reach statistical significance (P = 0.061). For all the remaining variables, the main effects for Group, main effects for Testing Session, and Group x Testing Sessions interactions were all non-significant. The greater somatosensory score for the tDCS group observed 1 day after the gait training and stimulation sessions may indicate that tDCS lead to an increased reliance on the proprioceptive system with a concomitant decreased reliance on the visual system in PD. However, this alteration in the control of balance did not result in an overall increase in balance performance in PD.
De Albuquerque, L. L.,
Landers, M. R.,
The Influence of Transcranial Direct Current Stimulation of the Motor Cortex on Balance in Parkinson's Disease.