The Effects Of Brain Stimulation On Balance Control In Parkinson's Disease

A constant transcranial direct current stimulation (tDCS) is delivered using a battery-driven stimulator (DC-StimulatorPlusTM, NeuroConn, Ilmenau, Germany) with anodal (5 × 7 cm2), and cathodal (10 × 10 cm2) water-soaked sponge electrodes with an intensity of 1 mA during 20 min over 4 sessions. The anode electrode is placed over the left dorsolateral prefrontal cortex (LDLPFC), corresponding to F3 in the 10-20 EEG system. The cathode electrode is placed over the right orbitofrontal cortex. Two straps is used to affix the electrodes. A fitted head cap (Artinis Medical Systems, The Netherlands) is applied to keep the electrodes in place and to assure that the electrodes have full contact to the scalp. This method of LDLPFC localization has been used before in several tDCS studies on cognitive function, and motor function, which has been regarded as a relatively accurate method of localization by neuroimaging techniques. For real stimulation, constant current is increased to 1 mA in a ramp-like fashion over 15 seconds, holds constant at 1 mA for 19 mins and 30 seconds, and then decreases over 15 seconds. Sham stimulation included 15 seconds of ramping the stimulation up to 1 mA and then immediately down again at the beginning and the end of intervention; this is to control for the participants physical sense of stimulation associated with current changes. This design is a reliable control as sensations resulting from tDCS become negligible after the initial minute of stimulation. The tDCS intervention is administered by a PhD candidate. Each participant attends four sessions, which including real tDCS with firm standing, real tDCS with foam standing, sham tDCS with firm standing and sham tDCS with foam standing. Under the firm standing condition, participants are instructed to stand directly on the platform with both feet hip width apart and focus on their balance. When participants under the foam standing, they are demonstrated to position themselves in the centre of medium density foam block (74.5cm x 62cm x 15.7cm) (Qiu, Cole et al. 2013). In order to monitor fidelity to the intervention, another investigator is onsite during the tDCS stimulation. Prior to the tDCS stimulation, participants are informed the study protocol. Participants are allowed to inform investigator if they need extra rest or are willing to stop from participating during each session. The study has been designed as a cross over study and the interval between tDCS sessions is seven days, as this interval has been used in previous tDCS studies to effectively wash out any potential after effects (Fregni, Boggio et al. 2005, Fregni, Gimenes et al. 2006, Vanderhasselt, De Raedt et al. 2013).