Neuromodulation Using Transcranial Direct Current Stimulation to Improve Dual-Task Performance in People with Parkinson's Disease
Mishra, Ram Kinker
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Despite advances in pharmacological treatments and surgical processes, the problem of postural instability and cognitive impairments persists in people with Parkinson’s disease (PD). These symptoms deteriorate further under dual-task conditions. Dual-tasking is common in every-day life; therefore, it has become a crucial aspect of PD rehabilitation. Recently, transcranial direct current stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) has shown the potential to improve dual-tasking in patients with PD. However, there is inconsistency in the results reported in the literature. One of the primary reasons for heterogeneous findings is the gap in understanding about the timing of tDCS priming relative to task performance. To address this gap, in this dissertation, the online and sustained effects of left DLPFC stimulation with anodal tDCS was investigated to determine time-dependent tDCS priming. We recruited twenty participants with PD in a double-blinded, sham-controlled, and cross-over study. Each subject completed two visits separated by a minimum of a one-week wash-out period. The left DLPFC was stimulated using anodal tDCS with 2mA current intensity for 30 minutes. Each subject performed dual-task during gait and timed up and go (TUG) with phonemic verbal fluency task given as the secondary cognitive task. Moreover, the motor-cognitive performance was evaluated using instrumented trail making tests (iTMT). The effect of tDCS on dual-task performances was assessed during, immediately after, post 15, and 30 minutes of stimulation. The gait performance was assessed using gait speed, stride time variability, and stride length. The functional-mobility was evaluated in terms of time taken to complete the sub-component of TUG (sit-to-stand transition, turning180o, stand-to-sit, and straight walk). Cognitive task performance was measured using the number of words generated. The iTMT test performance was quantified by using average ankle velocity and time taken to complete iTMT tasks. We found a significant increase (p=0.023) in gait speed under dual-task conditions due to anodal tDCS compared to sham. However, there was no significant effect of tDCS on TUG performance. Moreover, anodal tDCS led to a greater improvement (p=0.017) in motor performance during iTMT, as demonstrated through an increase in ankle velocity compared to sham. Anodal tDCS also led to more significant improvement in cognitive task performance when performed concurrently with walking (p<0.01) or TUG (p<0.01). In conclusion, the left DLPFC stimulation using anodal tDCS can improve dual-task performance in patients with PD. The effects of tDCS on dual-tasking can be task-specific as gait speed and cognitive performance improved post-stimulation, but there were no tDCS related changes in TUG performance. Furthermore, anodal tDCS improved iTMT related motor performance peaked during stimulation but not post-stimulation.