Table 1. Summary of recent randomized controlled trials of tDCS in AD and MCI.
| Study | Participants | Active tDCS | Sham tDCS | Intensity, dose, and duration | Combination with another intervention | Assessment outcomes | Findings |
|---|---|---|---|---|---|---|---|
| Rasmussen et al.83 | Mild-to-moderate AD (n=19: active=10; sham=9) | Anodal: left DLPFC | For 1 min, same montage | 2-mA HD-tDCS for 20 min/session, 3 sessions/day for 2 days (total 6 sessions) | None | MMSE, clock-drawing test, TMT part A, RBANS, MRI including DTI | Short-term improvement in delayed-recall memory and global cognition. Positive correlation between FA in the anterior thalamic radiation with delayed memory score |
| He et al.82 | MCI (n=43: active=24; sham=19) | Anodal: left DLPFC | For 1 min, same montage | 1-mA HD-tDCS for 20 min/day, 5 sessions/week for 2 weeks (total 10 sessions) | None | MMSE, MoCA, resting-state fMRI | No improvement in cognition. Altered intensity and synchrony of brain activity in multiple regions on fMRI |
| Gangemi et al.43 | Mild AD (n=26: active=13 and 9; sham=13 and 9) | Anodal: left frontotemporal | For 10 sec, same montage | Study 1: 2 mA for 20 min/day for 10 days (total 10 sessions) Study 2: 10 days/month for 8 months (total 80 sessions) |
None | MMSE, MODA, EEG | Both short-term and long-term effects on the prevention of cognitive decline |
| Im et al.38 | Mild AD (n=18: active=11; sham=7) | Anodal: left DLPFC Cathodal: right DLPFC |
30-sec ramp up and 30-sec ramp down, same montage | 2 mA for 30 min/day for 6 months (total 180 sessions) | None | MMSE, CDR and CDR-SOB, digit span, BNT, RCFT, SVLT, executive function tests, [18F]FDG PET | Long-term improvements in global cognition and language function. Marginally improved executive functions. Left middle/inferior temporal glucose metabolism was preserved on PET |
| Lu et al.44 | MCI (n=201: active=69 and 68; sham=64) | Anodal: left lateral temporal cortex | For 30 sec, same montage | 2 mA, 20 min/day, 3 sessions/week for 3 months (total 36 sessions) | WMT | N-back task, ADAS-Cog, MMSE, CDR-SOB, NPI, CVFT, digit span, logical memory, TMT | The combined tDCS-WMT group showed greater short-term improvements in delayed-recall and working memory, and long-term improvement in logical memory relative to single-modality groups |
| Gomes et al.110 | MCI (n=58: active=29; sham=29) | Anodal: left DLPFC | For 30 sec, same montage | 2 mA, 30 min/day, 2 sessions/week for 5 weeks (total 10 sessions) | None | CAMCOG, MMSE, TMT, semantic verbal fluency (animals), BNT, clock-drawing test, word-list memory, direct and indirect digit order, N-back task | Short-term improvement in memory recall, verbal fluency, and executive functioning |
| Khedr et al.80 | Mild-to-moderate AD (n=46: active=23; sham=23) | Anodal: left and right temporoparietal | For 30 sec, same montage | 2 mA, 20 min/day, 5 sessions/week for 2 weeks (total 10 sessions) | None | MMSE, MoCA, clock-drawing test, Cornell depression scale, serum tau, Aβ 1–42, lipid peroxidase | Short-term improvement in global cognition and depression, also correlated with increased plasma Aβ 1–42 levels. |
| Bystad et al.45 | Mild-to-moderate AD (n=25: active=12; sham=13) | Anodal: left temporal Cathodal: right frontal |
For 30 sec, same montage | 2 mA, 30 min/day, 6 sessions in 10 days (total 6 sessions) | None | MMSE, CVLT, clock-drawing test, TMT, WAIS, Cornell depression scale | No significant improvement in cognition |
| Yun et al.81 | MCI (n=16: active=8; sham=8) | Anodal: left DLPFC Cathodal: right DLPFC |
For 20 sec, same montage | 2 mA, 20 min/day, 3 sessions/week for 3 weeks (total 9 sessions) | None | Modified MMQ, [18F]FDG PET | Short-term improvement of the memory strategies, increased regional cerebral metabolism on PET |
| Khedr et al.84 | Mild-to-moderate AD (n=34: active=11 and 12; sham=11) | Anodal: left DLPFC Cathodal: left DLPFC |
For 30 sec, same montage | 2 mA, 25 min/day, daily for 10 days (total 10 sessions) | None | MMSE, WAIS-III motor cortical excitability, P300 event-related potentials | Both anodal and cathodal tDCS improved short-term cognition and reduced the P300 latency |
| Cotelli et al.46 | Mild-to-moderate AD (n=36: active=12 and 12; sham=12) | Anodal: left DLPFC | For 20 sec at the beginning and end, same montage | 2 mA, 25 min/day, 5 sessions/week for 2 weeks (total 10 sessions) | Individualized computerized memory training | FNAT, MMSE, ADL, IADL, Tinetti scale, NPI, Picture naming task, BADA, RBMT, Rey Auditory Verbal Learning Test, complex figure copying, TMT | No significant additive effect on the general improvement by memory training |
| Suemoto et al.47 | Moderate AD (n=40: active=20; sham=20) | Anodal: left DLPFC | For 20 sec, same montage | 2 mA, 20 min/day, 3 sessions/week for 2 weeks (total 6 sessions) | None | Apathy Scale, NPI, ADAS-Cog | No significant difference in apathy or cognition |
AD, Alzheimer’s disease; ADAS-Cog, Alzheimer’s Disease Assessment Scale–Cognitive Subscale; ADL, activities of daily living; BADA, Battery for Analysis of Aphasic Deficits; BNT, Boston Naming Test; CAMCOG, Cambridge Cognition Examination; CDR, Clinical Dementia Rating; CDR-SOB, Clinical Dementia Rating–Sum of Boxes; CVFT, Category Verbal Fluency Test; DLPFC, dorsolateral prefrontal cortex; DTI, diffusion-tensor imaging; EEG, electroencephalography; FA, fractional anisotropy; fMRI, functional magnetic resonance imaging; FNAT, Face–Name Association Memory Task; HD, high definition; IADL, Instrumental Activities of Daily Living; MCI, mild cognitive impairment; MMQ, Multifactorial Memory Questionnaire; MMSE, Mini-Mental Status Examination; MoCA, Montreal Cognitive Assessment; MODA, Milan Overall Dementia Assessment; MRI, magnetic resonance imaging; NPI, Neuropsychiatric Inventory; PET, positron-emission tomography; RBANS, Repeatable Battery for the Assessment of Neuropsychological Status; RBMT, Rivermead Behavioral Memory Test; RCFT, Rey Complex Figure Test; SVLT, Seoul Verbal Learning Test; tDCS, transcranial direct current stimulation; TMT, Trail-Making Test; WAIS, Wechsler Adult Intelligence Scale; WMT, working memory training.