Table 2 Methodological characteristics of the studies included in the systematic review following the determination of the PICOS terms
First Author (Year) | - Groups (n = number of participants; mean ± standard deviations (year); UPDRS III (score); PD time (year); LED (mg/day)) • Study design | tDCS 1. Current Stimulation 2. Sham characteristics 3. Electrode place (anode/cathode) 4. Duration 5. Intensity 6. Electrode size (cm2) 7. Number of sessions | Intervention 1. Type (acute/chronic) 2. Characteristics (strength, gait, cognition, etc) 3. Volume (only chronic); Intensity; duration 4. Moment 5. Number of sessions | A. Assessment period B. Medication state C. Outcomes (methods/equipment) |
Biundo (2015) [33] | - Cognitive Training + active tDCS (n = 12; 69.1 ± 7.6; NR; NR; NR) - Cognitive Training + sham tDCS (n = 12; 72.3 ± 4.1; NR; NR; NR) • Parallel, double-blind, randomized trial | 1. Anodic 2. NR 3. Left DLPFC/contralateral supraorbital area 4. 20 min 5. 2 mA 6. NR 7. 16 sessions | 1. Chronic 2. Computer-based cognitive training 3. 4 days a week; Rehacom software®; 30 min 4. NR 5. 16 sessions | A. Pre, post, and follow-up (16 weeks) B. NR C. Attention/executive skills (Written coding test); memory (immediate memory index and delayed memory index); disease severity (UPDRS III) |
Broeder (2019) [28] | - tDCS + writing Parkinson group (n = 10; 63.2 ± 9.2; 17.5 range (13–22); 6.9 ± 5.1; 407 ± 300.4) • Cross-over, single-blind, randomized | 1. Anodic 2. Current applied for the 30s 3. Left M1/ right supraorbital area 4. 20 min 5. 1 mA 6. 35 cm2 7. 1 session | 1. Acute 2. Writing 3. 3 bouts of writing several sequences of letters (3 min) followed by execution of the funnel task; 20 min 4. During tDCS 5. 1 session | A. Online effect B. ON state C. Number of upper limb freezing Episodes (funnel task on a touch-sensitive tablet) |
Broeder (2019) [34] | - tDCS + writing Parkinson group (n = 10; 63.2 ± 9.2; 17.5 range (13–22); 7.0 ± 5.1; NR) • Cross-over, single-blind, randomized controlled trial | 1. Anodic 2. NR 3. Left M1/Right supraorbital area 4. 20 min 5. 1 mA 6. 35 cm2 7. 1 session | 1. Acute 2. Writing 3. Writing of loops in different patterns (continuous and alternating) and sizes (0.6 and 1.0 cm) during 3 trials (2 min 24 s each) followed by execution of the funnel task (5 trials of 1 min each); 20 min 4. During tDCS 5. 1 session | A. Pre, during, post (30 min after training) and follow-up (1 week) B. ON state C. writing performance on tablet (amplitude, velocity, coefficients of variation); writing performance on paper (mean writing size, writing velocity and writing quality/Systematic Screening of Handwriting Difficulties test); motor cortex excitability – MEP, CSP, RMT and SICI (TMS) |
Costa-Ribeiro (2016) [31] | - tDCS + gait training (n = 11; 61.1 ± 9.1; 19 ± NR; 6.1 ± 3.8; 740.9 ± 924.3) - Sham + gait training (n = 11; 62 ± 16.7; 19.1 ± NR; 6.3 ± 3.7; 890.9 ± 836) • Parallel, double-blind, randomized controlled trial | 1. Anodic 2. Current applied for 30s 3. SMA/supraorbital area over the hemisphere of the most affected side 4. 13 min 5. 2 mA 6. 35 cm2 7. 10 sessions | 1. Chronic 2. Visually cued gait training (Subjects were instructed to walk at the step length indicated by white strips (visual cue) along a 6.5-m walkway) 3. 3 times a week; 24 min of active training, with a 6 min interval (30 min total) 4. After tDCS session 5. 10 sessions | A. Pre, post (48 h after training) and follow-up (1 month) B. ON and OFF state C. Functional mobility (TUG); motor cortex excitability – MEP (TMS) |
Costa-Ribeiro (2017) [35] | - Cued gait training + tDCS (CGT + tDCS) (n = 11; 61.1 ± 9.1; 19.0 ± 4.9; 6.1 ± 3.8; 740.9 ± 924.3) - Cued gait training + sham (CGT + sham) (n = 11; 62.0 ± 16.7; 17.6 ± 5.1; 6.3 ± 3.7; 890.9 ± 836.0) • Parallel, double-blind controlled, randomized clinical trial | 1. Anodic 2. The stimulator was turned off after 30 s 3. M1/supraorbital area of the contralateral hemisphere of the most affected side 4. 13 min 5. 2 mA 6. 35 cm2 7. 10 sessions | 1. Chronic 2. The gait training associated with visual cues was aimed to improve functional mobility 3. 3 days a week; NR; 30 min 4. After the tDCS 5. 10 sessions | A. Pre, post, and follow-up (1 month) B. ON state C. Functional mobility (TUG, 10-m walk test); Cadence, stride length (video camera); Motor Impairment (UPDRS III); Bradykinesia (sum of scores on UPDRS items 23–26 and UL-MT); Balance (BBS); Quality of life (PDQ-39) |
Criminger (2018) [36] | tDCS (Sitting, Bike, Wii, Sham) (n = 16; 68.13 ± 9.76; 23.44 ± 9.73; 8.69 ± 9.76; NR) • Cross-over, single-blind, randomized controlled trial | 1. Anodic 2. Current applied for 30s (1 to 0 mA) 3. Left DLPFC/ right DLPFC 4. 20 min 5. 2 mA 6. 15cm2 7. 1 session | 1. Acute 2. Bike/Wii (golf) 3. Bike: self-reported intensity level of 12–14 on the Borg Rating of Perceived Exertion Scale, Wii: NR; 20 min 4. During tDCS 5. 1 session | A. Post each session B. ON state C. Dual-task performance during walking (TUG and TUG with dual task (motor and cognitive task); dual-task cost- DTC. |
Fernández-Lago (2017) [37] | - treadmill - treadmill + tDCS - treadmill + sham (n = 18; 56.67 ± 11.63; 21.17 ± 11.31; 6.17 ± 3.65; 733.2 ± 496.2a) • Cross-over, randomized | 1. Anodic 2. 2 mA and turn off after 8 s 3. Motor cortex/ contralateral supraorbital area 4. 20 min 5. 2 mA 6. 3.5 cm2 7. 1 session | 1. Acute 2. Treadmill walking 3. 1 day a week; Individual velocity obtained during overground walking at the beginning of each experimental session (PRE) was used for the subsequent treadmill walking conditions; 20 min 4. During tDCS 5. 1 session | A. Pre and post each session B. ON state C. Gait (Optogait, Microgait); Neurophysiologic measurements: Electromyography, Reciprocal Ia Inhibition, H-reflex amplitude, MEP; SICI, ICF (EMG and TMS) |
Forogh (2017) [38] | - tDCS + occupational therapy (n = 12; 61.33; NR; NR; NR) - Sham + occupational therapy (n = 11; 64.11; NR; NR; NR) • Parallel, double-blind, randomized clinical trial. | 1. Anodic 2. Current applied for 30s 3. Left DLPFC/Right DLPFC 4. 20 min 5. 2 mA 6. 35 cm2 7. 8 sessions | 1. Chronic 2. Occupational therapy 3. 4 days a week (2 week); NR; NR. 4. After tDCS 5. 8 sessions | A. Pre, post and follow-up (3 months) B. NR C. Fatigue (Fatigue Severity Index); Daytime Sleepiness (Epworth Sleepiness scale) |
Horiba (2019) [39] | - tDCS + mirror visual feedback (n = 9; 71.33 ± 4.15; 13 ± 5.56; 6.44 ± 3.16; 324.00 ± 121.11) - Sham + mirror visual feedback (n = 9; 70.67 ± 3.85; 17.11 ± 6.10; 6.44 ± 3.28; 251.56 ± 157.63) • Parallel, double-blind, randomized clinical trial. | 1. Anodic 2. Current applied for 30s 3. Right M1/frontal orbit 4. 20 min 5. 2 mA 6. 80 cm2 7. 1 session | 1. Acute 2. Motor skill training using mirror visual feedback 3. 4 sessions of 30 s of execution and 30 s of rest for 5 min each session; observe the movements of the right hand in a mirror that provided mirror visual feedback of their performance in the ball rotation task; 20 min. 4. During tDCS 5. 4 sessions (1 day) | A. Pre and post B. OFF state C. Upper limb motor function (Number of ball rotations /video camera analysis, peak acceleration/infrared cameras and reflective markers, maximal pinching force), and disease severity (UPDRS III). |
Ishikuro (2018) [40] | - Anodal tDCS + Physical therapy (n = 9; 77.5 ± 4.8; NR; 5.77 ± 2.03; NR) - Cathodal tDCS + Physical therapy - Sham tDCS + Physical therapy • Cross-over, randomized clinical trial. | 1. Anodic and Cathodic 2. Current applied for 30s 3. Frontal polar area/occipital area 4. 15 min 5. 1 mA 6. 35 cm2 7. 5 sessions | 1. Chronic 2. Physical therapy for upper extremities (stretching and muscle strength exercise) while sitting in a chair 3. 5 days a week; 15 min 4. During tDCS 5. 5 sessions for each condition. | A. Pre, post 1 (1 session), post 2 (3 sessions) and post 3 (5 sessions). Post 1 and post 2 performed only for the STEF B. OFF state C. Disease severity (UPDRS III); Sensory-motor functions (Fugl Meyer Assessment set); Ability to pinch, grasp, and transfer objects (STEF); Executive function (TMT-A) |
Kaski (2014) [25] | - tDCS + Physical training (n = 8; NR; NR; NR) - tDCS without physical training (n = 8; NR; NR; NR) • Cross-over, double-blind, randomized controlled trial | 1. Anodic 2. The current (2 mA) was turned off after 30 s 3. Bilateral M1 and PMC/ inion 4. 15 min 5. 2 mA 6. 40 cm2 7. 1 session | 1. Acute 2. Gait initiation, stride length, gait velocity, arm swing, and balance 3. 15 min 4. During tDCS 5. 1 session | A. Pre and post B. ON state C. Gait (TUG, 6-min walk, and video analysis); Balance (Quantitative pull test, SwayStar System®, Balance Int. Innovations GmbH, Switzerland). |
Kaski (2014) [41] | - Dance + tDCS - Dance + sham (1 person; 79; 34; 7; 856,25 + Piribedil 100 mg) • Cross-over, double-blind, randomized | 1. Anodic 2. 2 mA for only 30s and then turned off 3.Bilateral M1 and PMC/ inion 4. 7 min 30 s 5. 2 mA 6. 40 cm2 7. 2 sessions for each training (interval of 1 week) | 1. Acute 2. Dance – tango 3. 2 music; 7 min 30 s 4. During tDCS 5. 2 sessions | A. Pre and post B. ON state C. Angular trunk movement during the dancing (digitally-based angular-velocity transducers); gait (Tinetti Gait Index) |
Lawrence (2018) [42] | - Standard Cognitive Training (Standard CT) (n = 5; 68.14 ± 8.69; NR; 5.29 ± 4.23; 295 ± 313.40 - Tailored Cognitive Training (Tailored CT) (n = 6; 65.57 ± 5.20; NR; 5.79 ± 4.97; 383 ± 178.62 - tDCS (n = 7; 72 ± 6.45; NR; 5.50 ± 5.66; 573.29 ± 586.25 - Standard Cognitive Training + tDCS (Standard CT + tDCS) (n = 7; 63.57 ± 15.68; NR; 6.79 ± 4.60; 350.71 ± 322.37 - Tailored Cognitive Training + tDCS (Tailored CT + tDCS) (n = 7; 67.43 ± 6.37; NR; 4.43 ± 2.70; 464.29 ± 358.78 - Control Group (CG) (n = 6; 72.29 ± 6.21; NR; 5.36 ± 4.14; 292.88 ± 274.51 • Parallel, randomized controlled trial | 1. Anodic 2. NR 3. Left DLPFC/ left supraorbital area. 4. 20 min 5. 1.5 mA 6. 35 cm2 7. 4 sessions | 1. Chronic 2. Cognitive training (Smartbrain Pro™): Standard (Two predetermined activities for each cognitive domain - memory, attention/working memory, language, executive function, visuospatial) or Tailored (activities individualized to participants baseline neuropsychological test results). 3. 3 days a week; difficulty levels of each activity were adjusted individually; 45 min 4. Separated of tDCS session 5. 12 sessions | A. Pre, post (week 5), and follow-up (week 12) B. ON state C. Neuropsychological assessment (executive function, attention - working memory, memory, visuospatial abilities, language, global cognitive, activities of daily living and quality of life) |
Manenti (2016) [29] | - Physical therapy + tDCS (n = 10; 69.0 ± 9.1; 27.8 ± 13.9; 7.1 ± 3.6; 524.6 ± 179.1) - Physical therapy + sham (n = 10; 69.1 ± 5.6; 27.6 ± 8.9; 7.8 ± 4.2; 815.7 ± 590.9) • Parallel, double-blind, randomized | 1. Anodic 2. 2 mA for only 10s and then turned off and turned on in the last 10s 3. DLPFC contralateral to the most affected body side/contralateral supraorbital area 4. 25 min 5. 2 mA 6. 35 cm2 7. 10 sessions | 1. Chronic 2. Focused on the core areas of motor impairment in PD, such as the inability to initiate movement, difficulties with balance and gait control, falls, and deficits in the pacing of rhythmic movements. 3. 5 days a week; 25 min 4. During tDCS 5. 10 sessions | A. Pre, post, and follow-up (3 months) B. ON state C. Cognition (MMSE, PD-CRS, Digit span, Cantab Paired Associated Learning, TMT, FAB, Semantic fluency, Cantab Reaction Time Index); clinical evaluation (UPDRS-III, HY, BDI-II, PDQ-39, RBDSQ); motor function (TUG, Four Square Step Test, Standing Stork Test, Sit and Reach Test) |
Manenti (2018) [43] | - tDCS + computerized cognitive training (n = 11; 65.5 ± 6.4; 26 ± 10.3; 6.2 ± 3.9; 618.6 ± 304.4) - Sham + computerized cognitive training (n = 11; 63.8 ± 7.1; 22.7 ± 7.8; 7.6 ± 3.4; 559.8 ± 306.5) • Parallel, double-blind, randomized | 1. Anodic 2. 2 mA for only 10s and then turned off and turned on in the last 10s 3. left DLPFC/right supraorbital area 4. 25 min 5. 2 mA 6. 35 cm2 7. 10 sessions | 1. Chronic 2. BrainHQ (Posit Science) – exercise focused on attention, memory, brain speed, people skills, navigation and intelligence. Five exercises of 5 min for each session. 3. 5 days a week for 2 weeks; 25 min 4. During tDCS 5. 10 sessions | A. Pre, post and follow-up (3 months) B. ON state C. Clinical and disease severity (PDQ-39, BIS-11, RBDSQ, Apathy Evaluation Scale, UPDRS III, H&Y); Cognitive functions (MMSE; PD-CRS, Digit span, Rey Auditory Verbal Learning Test, Object and action IPNP, TMT, FAB, phonemic and Semantic fluency, Stroop); depressive symptoms (BDI-II) |
Schabrun (2016) [44] | - Active tDCS + dual-task gait training (n = 8; 72 ± 4.9; 47.7 ± 7.5; 6.9 ± 4.4; 730 ± 341 - Sham + dual-task gait training (n = 8; 63 ± 11.0; 37.7 ± 9.8; 4.6 ± 3.9; 523 ± 398 • Parallel, double-blind, randomized, sham-controlled | 1. Anodic 2. Ramped up over 10 s, down over 10 s and then switched off. 3. M1/contralateral supraorbital area 4. 20 min (In the first 20 min of Dual-task gait training) 5. 2 mA 6. 35 cm2 7. 9 sessions | 1. Chronic 2. Gait training + cognitive task 3. 3 days a week; progressive complexity; 60 min 4. During tDCS 5. 9 sessions | A. Pre, Post, and follow-up (12 weeks) B. ON state C. Gait, Gait + cognitive task (GAITRite® and TUG); bradykinesia (clinical test); visuomotor speed and procedural learning (Serial Reaction Time Task). |
Yotnuengnit (2018) [45] | - tDCS (n = 18; 64.4 ± 7.8; 10,89 ± 4,75; 7,9 ± 3,9; 849,1 ± 397,1) - tDCS + physical therapy (n = 17; 68.2 ± 9.8; 11,94 ± 4,68; 9,4 ± 5,3; 829,0 ± 360,6) - Sham + physical therapy (n = 18; 62.7 ± 2.8; 11,17 ± 3,97; 6,6 ± 3,6; 912,0 ± 472,9) • Parallel, double-blind, randomized controlled trial | 1. Anodic 2. 2 to 0 mA in the first minute 3. M1/ right supraorbital area 4. 30 min 5. 2 mA 6. 35 cm2 7. 6 sessions | 1. Chronic 2. Joint range of motion and body flexibility, strengthening leg muscles, balance and gait training 3. 3 days per week; 30 min 4. After tDCS 5. 6 sessions | A. Pre, Post, and follow-up (2 and 6 weeks) B. ON state C. Gait (The Gait & Motion Analysis); Disease severity (UPDRS) |