Table 5.
Summary of main results of the selected studies of tDCS in AD.
| References | Participants | Procedure and brain region/s involved | Intervention for active groups | Current intensity and electrodes position according to the 10-20 EEG international system | Neuropsychological assessment/experimental cognitive tasks | Follow-up | Main findings of the active group/s at the end of the intervention |
|---|---|---|---|---|---|---|---|
| Ferrucci et al. (50) | 10 patients Sex: M = 3; F = 7; Mean age: 75.2 ± 7.3; Pharmacotherapy: ChEI |
Anodal, cathodal or sham tDCS of the TPC | 3 sessions at intervals of 1 week | Anodal or cathodal 1.5 mA current delivered for 15 min bilaterally over the TPC (P3-T5 left side; P4-T6 right side); Cathodal electrode: right deltoid muscle |
Word recognition task (modified from Adas-cog); c-attentional cue task (E-Prime computer-controlled Posner paradigm) | - | Word recognition memory improvement after anodal tDCS |
| Boggio et al. (51) | 10 patients Sex: M = 4; F = 6; Mean age: 79.1 ± 8.8 Pharmacotherapy: ChEI (not for all patients), BDZs, antipsychotics, TCAs |
Anodal tDCS of the TC, DPFC, or sham tDCS | 3 sessions at intervals of 48 h | 2 mA intensity delivered for 30 min over the left DLPFC (F3) or left TC (T3); Cathodal electrode: SO |
Stroop test; digit span (backward and forward); computer-based recognition memory task | - | Visual recognition memory improvement both after temporal and prefrontal tDCS |
| Boggio et al. (52) | 15 patients Sex: M = 8; F = 7 Mean age: 71.1 ± 5.8; Pharmacotherapy: not reported |
Anodal or sham tDCS of the TC | 5 consecutive days sessions | 2 mA current delivered for 30 min bilaterally (T3, T4) Cathodal electrode: right deltoid muscle |
MMSE, Adas-Cog, c-VRT, c-VAT | At 1 week and at 1 month | Visual recognition memory improvement and maintenance 4 weeks after the intervention |
| Khedr et al. (53) | 34 patients Sex: M = 19; F = 15 Mean age of anodal group: 68.5 ± 7.2 Mean age of cathodal group: 70.7 ± 5.4 Mean age of sham group: 67.3 ± 5.9 Pharmacotherapy: no patients took cholinomimetics, antidepressants, neuroleptics, sedative-hypnotics drugs for at least 1 week before assessment |
Anodal, cathodal or sham tDCS of the DLPFC | 10 daily sessions | 2 mA intensity delivered for 25 min Anodal/sham group: anodal electrode over the left DLPFC (F3), cathodal electrode: contralateral SO Cathodal group: cathodal electrode over the left DLPFC (F3), and anodal electrode over the contralateral SO |
MMSE, WAIS-III | At 1 and 2 months | Global cognition (MMSE) improvement both after anodal and cathodal tDCS |
| Suemoto et al. (54) | 40 patients Sex: M = 12; F = 28 Mean age of anodal group: 79.4 ± 7.1 Mean age of sham group: 81.6 ± 8.0 Pharmacotherapy: ChEI |
Anodal or sham tDCS of the DLPFC | 6 sessions over a period of 2 weeks | 2 mA intensity delivered for 20 min Anode electrode: left DLPFC (F3) Cathodal electrode: contralateral SO |
Adas-Cog | At 1 week | No improvement |
| Bystad et al. (20) | 25 patients Sex: M = 14; F = 11 Mean age of anodal group: 70.0 ± 8.0 Mean age of sham group: 75.0 ± 8.7 Pharmacotherapy: ChEI |
Anodal or sham tDCS of the TC | 6 sessions for 10 days | 2 mA intensity delivered for 30 min Anode electrode: left temporal lobe (T3) Cathodal electrode: right frontal lobe (Fp2) |
CVLT, MMSE, CDT, TMT | - | No improvement |
| Im et al. (12) | 18 patients Sex: M = 3; F = 15 Mean age of anodal group: 71.9 ± 9.2 Mean age of sham group: 74.9 ± 5.0 Pharmacotherapy: ChEI |
Anodal or sham tDCS of the DLPFC | Daily sessions for 6 months | 2 mA intensity delivered for 30 min Anode electrode: left DLPFC (F3) Cathodal electrode: right DLPFC (F4) |
MMSE, Digit span forward and backward, BNT, RCFT, CDT, SVLT, contrasting program, Go-No-Go test, COWAT, Stroop test | - | Improvement of global cognition (MMSE) and language (BNT); preventive decrease of executive functions |
| Khedr et al. (55) | 44 patients Sex: M = 26; F = 18 Mean age of anodal group: 64.2 ± 3.64 Mean age of sham group: 65.2 ± 4.5 Pharmacotherapy: Memantine and piracetam |
Anodal or sham tDCS of the right and left temporal lobe | 5 sessions/wk for 2 consecutive weeks | 2 mA intensity delivered for 20 min for each side Anode electrode: right TL/left TL (T3-P3/T4-P4) Cathodal electrode: deltoid muscle of the left arm |
Modified-MMSE, CDT, Montreal Cognitive Scale | - | A significant improvement in the total score of each cognitive rating scale in the real group |
| Gangemi et al. (56) | Study 1 26 patients Sex: M = 10; F = 16 Mean age of anodal group: 67.25 ± 2.8 Mean age of sham group: 69 ± 6.1 Study 2 18 patients Sex: M = 5; F = 13 Mean age of anodal group: 68.5 ± 2.8 Mean age of sham group: 68.7 ± 3.1 Pharmacotherapy: ChEI |
Anodal or sham tDCS of the left frontotemporal lobe | Study 1: daily sessions for 10 consecutive days Study 2: daily sessions for 10 consecutive days each month for 8 months | 2 mA intensity delivered for 20 min Study 1 Anode electrode: left frontotemporal lobe (F7-T3); Cathodal electrode: right frontal lobe (Fp2). |
MMSE MODA |
- | tDCS intervention was effective both in the short- and the long-term to slow down the progression of AD on temporal and personal orientation, attention, calculation, and recall |
| Gangemi and Fabio (57) | 26 patients Sex: M = 14; F = 12 Mean age of anodal group: 72 ± 4.4 Mean age of sham group: 75 ± 4.4 Pharmacotherapy: ChEI |
Anodal or sham tDCS of the left frontotemporal cortex | 10 sessions | Anode electrode: DLPFC (F3-F7), and left (F7) Cathodal electrode: right SO |
MODA subscales (temporal orientation, spatial orientation, personal orientation, family orientation, autonomy, reversal learning, verbal intelligence, story test, words production, token test, digital agnosia, constructive apraxia, Street test, attentional test) | - | Improvements of temporal orientation, spatial orientation, reversal learning, verbal intelligence, story test, word production and attention |
AD, Alzheimer's disease; ChEI, cholinesterase inhibitors; TPC, Temporoparietal Cortex; DBZs, benzodiazepines; TCAs, Tricyclic antidepressants, SSRIs, Selective serotonin reuptake inhibitors; TC, Temporal Cortex; DLPFC, Dorsolateral Prefrontal Cortex; MMSE, Mini Mental State Examination; Adas-cog, Alzheimer's Disease Assessment Scale-cognitive subscale; c-VRT, computerized Visual Recognition Task; WAIS-III, Wechsler Adult Intelligence Scale Third Edition; CVLT, California Verbal Learning Test; c-VRT, computerized Visual Recognition Task; WAIS-III, Wechsler Adult Intelligence Scale Third Edition; CDT, Clock Drawing Test; TMT, Trail Making Test; BNT, Boston Naming Test; RCFT, Rey Complex Figure Test; SVLT, Seoul Verbal Learning Test; COWAT, Controlled Oral Word Association Test; TL, Temporal lobe; MODA, Milan Overall Dementia Assessment; HD-tDCS, High-definition tDCS.