Effect of single‐session transcranial direct current stimulation on cognition in Parkinson's disease

Abstract

AimsNonmotor symptoms (NMS) such as cognitive impairment and impulse‐control disorders in Parkinson's disease (PD) remain a therapeutic challenge. Transcranial direct current stimulation (tDCS) has emerged as a promising alternative, although its immediate effects on NMS have been less well defined. In this randomized, sham‐controlled, crossover study, we aimed to explore the single‐session tDCS effects on cognitive performance in PD.MethodsTen nondemented patients with PD completed two sessions in counterbalanced order, receiving 20 minutes of either 2 mA anodal or sham tDCS over the left dorsolateral prefrontal cortex (DLPFC). During stimulation, they performed the visual working memory and go/no‐go tasks. Performance of the tasks was compared between the two conditions.ResultsSingle‐session anodal tDCS over the left DLPFC did not significantly improve cognitive tasks in PD compared with sham (P > .05).ConclusionSingle‐session tDCS is ineffective in improving visual working memory and inhibitory control in PD. Further research may worth exploring alternative tDCS parameters, ideally with repeated sessions and concomitant training.

Tolerability and Blinding of Transcranial Direct Current Stimulation in People with Parkinson’s Disease: A Critical Review

“…Study subjects had mild to moderate PD (Hoehn and Yahr (H&Y) range = 1.6–2.5). Two studies tested patients off dopaminergic medication [ 26 , 30 ] and three did not report medication status [ 24 , 27 , 32 ]. The study designs were heterogeneous: two studies were open-label (no subject or researcher blinding) [ 28 , 29 ]; three were parallel arm, randomized, double-blind, sham-controlled designs [ 25 , 27 , 32 ]; and four were crossover, randomized, sham-controlled designs, with two being double-blind [ 24 , 26 ], one being single-blind (subject) [ 31 ], and one with unstated blinding [ 30 ].…”

“…Two studies tested patients off dopaminergic medication [ 26 , 30 ] and three did not report medication status [ 24 , 27 , 32 ]. The study designs were heterogeneous: two studies were open-label (no subject or researcher blinding) [ 28 , 29 ]; three were parallel arm, randomized, double-blind, sham-controlled designs [ 25 , 27 , 32 ]; and four were crossover, randomized, sham-controlled designs, with two being double-blind [ 24 , 26 ], one being single-blind (subject) [ 31 ], and one with unstated blinding [ 30 ]. All but one study administered tDCS with intensities ≤ 2 mA (range of current densities = 0.03 mA/cm 2 – 0.08 mA/cm 2 ) for 15–25 min (mode = 20 min) and targeted frontal brain areas (i.e., the dorsolateral prefrontal cortex (DLPFC), frontal polar area) [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]; the other study used 2 and 4 mA intensities for 20 min and targeted the cerebellum [ 24 ].…”

Transcranial Direct Current Stimulation to Enhance Cognitive Impairment in Parkinson's Disease: A Systematic Review and Meta-Analysis

“…Lau et al ( 29 ) applied 2 mA to the L-DLPFC in 10 subjects with PD without cognitive compromise, locating the cathode in SOAC. The researchers evaluated VWM and emotional inhibitory control using experimental paradigms.…”

“…For each analysis, a z -test was performed to derive a summary p -value. Lau et al's ( 29 ) study was excluded since needed data for effect-size calculation could not be extracted, while a social cognition meta-analysis could not be performed because Adenzato et al's ( 30 ) study was the only one to provide such measure.…”

“…As primary outcomes we considered: (1) Measures of executive functions: Problem-solving strategies: The Stockings of Cambridge (SOC) subtest of CANTAB ( 31 ); Task-Switching: the Wisconsin Card Sorting Test (WCST), the Trail Making Test B (TMT-B) ( 32 , 33 ); working memory: the Three-back letter task ( 34 ), Visual working memory (VWM), the change detection task ( 29 ), the working memory test (WM) ( 33 ); inhibition: Stroop Test (Color-word interference) ( 31 – 33 ); verbal and phonological fluency: the Verbal Fluency Test ( 32 ), the Controlled Oral Word Association Task (COWAT) ( 31 ) and tasks of semantic and phonological fluency ( 35 ); (2) Measures of visual attention: the TMT-A ( 32 ), the number-letter sequence (LNS) ( 31 ); (3) Measures of memory: the Hopkins Verbal Learning Test-Revised (HVLT-R) Immediate recall test, the Paragraph Recall Test ( 31 ); (4) Measures of visuospatial skills: the Line Orientation Judgment Test (JLO) and Hooper's Visual Organization Test (HVOT) ( 31 ); (5) Measures of language: the Boston Naming Test-Short Form (BNT), the similarity test ( 31 ); (6) Measures of theory of mind: the Reading the Mind in the Eyes task, the Attribution of Intentions (AI) task ( 30 ); (8) Measures of procedural learning: Probabilistic Classification Learning (PCL) ( 33 ); (9) Measures of the inhibition of emotional response: the emotional go/no-go paradigm ( 29 ).…”