Table 2: Studies investigating tES as a therapeutic tool in ADRD.

Studies investigating tES for treatment of ADRD using clinical or biomarker diagnostic criteria. Age is shown as Mean±SD. LBD = Lewy body dementia. CVLT = California Verbal Learning Test; TMT = Trail Making Test; MMSE = Mini-Mental State Examination; MMQ = Multifactorial Memory Questionnaire; PMIT = Picture Memory Impairment Test; MOCA = Montreal Cognitive Assessment; ADAS-Cog = Alzheimer’s Disease Assessment Scale-cognitive; BDS = Blessed Dementia Scale; DAD = Disability Assessment for Dementia; D-KEFS = Delis-Kaplan Executive Function System; WMS = Wechsler Memory Scale; RBANS = Repeatable Battery for the Assessment of Neuropsychological Status; BADA = Battery for the Analysis of the Aphasic Deficit; AHRS = Auditory Hallucinations Rating Scale.

Electrical Stimulation Studies 2016–2018	Criteria for AD/MCI and disease stage	No. of Participants	Type of Stimulation	Sham/Control	Interleaved Cognitive Stimulation	Age	Target area; localization method	Scalp Electrode 1	Scalp Electrode 2	Scalp Electrode size (cm2)	Extracranial Electrode and size (cm2)	Current	Duration (min)	Total Number of Sessions; Length of Intervention	Cognitive Domain	Neuropsychological Tests – Primary Outcome	Neuropsychological Tests – Secondary Outcomes	Main Significant Neuropsychological Findings
Pilot Studies and RCTs
Bystad, et al.; 2016.	Probable AD with increased level of certainty by NINCDS-ADRDA; MMSE > 18	25	tDCS; awake	1:1 Treatment:Sham	No	Treatment group age=70.0±8.0; Sham group age=75.0±8.7	L temporal lobe; 10–20 system	Anode = T3	Cathode = Fp2	35	None	2 mA	30	6 sessions; 10 days	Verbal Memory	CVLT-II	MMSE, TMT A, TMT B, clock-drawing test	No significant differences in CVLT-II, MMSE, TMT A, TMT B, or clock drawing test were seen between the treatment and sham group.
Yun, et al,; 2016.	MCI diagnosis by Peterson criteria	16	tDCS; awake	1:1 Treatment:Sham	No	Treatment group Age = 74.8±7.5; Sham group Age = 73.1±4.2	Bilateral DLPFC; 10–20 system	Anode = F3	Cathode = F4	25	None	2 mA	30	6 sessions; 10 days	Subjective Memory Complaint Scale from Participants, FDG-PET	MMQ	n/a	The treatment group showed improvement in subjective memory scores on the MMQ-A (ability) and MMQ-C (contentment) subscores compared to sham.
Ladenbauer; et al.; 2017.	Amnestic MCI (single or multidomain) by Mayo criteria, with objective cognitive decline with scores < 1 SD below norms on memory tests; MMSE >=24	16	Slow oscillatory tDCS; delivered during a daytime nap	Balanced crossover design, each participant received 1 treatment and 1 sham session, at least 2 weeks apart	No	Age=71±9	Bifrontal stimulation, using anodal current with sinusoidal oscillations at a frequency of 0.75 Hz; 10–20 system	F3	F4	8 mm diameter	Bilateral Mastoids; 0.64	0.522 mA/cm2	15–25 (5 minute blocks of stimulation given during stage 2,3, or 4 NREM sleep, for a total of 3–5 blocks)	1 session; 1 day	Visual recognition memory, EEG	Visuospatial Memory Task comprised on neutral pictures taken from the International Affective Picture System	Procedural fingertapping task, verbal memory task, location memory task	There was an improvement in visual recognition memory in the treatment group compared to sham when controlling for sleepiness. There was no effect of treatment on procedural memory, verbal memory, or location memory.
Murugaraja, et al.; 2017	MCI diagnosis by NIA-AA criteria, CDR=0.5	11	tDCS; awake	None	No	Age=59.6	L DLPFC; 10–20 system	Anode = F3-FP1	Cathode = R supra-orbital region	35	None	2 mA	20	5 sessions; 5 days	Visual Memory	PMIT	n/a	Improved immediate and delayed recall on the PMIT immediately after conclusion of the treatment. Improvement on delayed recall PMIT persisted 1 month later
Cruz Gonzalez, et al.; 2018	MCI diagnosis by modified Peterson’s criteria, MOCA 19–26, CDR <=0.5	5	tDCS; awake	A-B-C-A protocol; anodal tDCS + CS, sham tDCS + CS, and CS only	Yes	Age=72.8±6.6	L DLPFC; 10–20 system	Anode = L DLPFC	n/a	35	R deltoid; 35	2 mA	30	1–5 sessions total of active tDCS + cognitive stimulation	Not Specified	Not specified	Performance on Cognitive Stimulation tasks from Neuron Up, MOCA, Digit Span, TMT	There was an improvement on the Neuron Up task in three subjects who received three or more tDCS sessions
Manenti, et al.; 2017.	Amnestic MCI by Petersen criteria, MMSE 24–30, CDR=0.5	18	tDCS; awake	1:1 Treatment:Sham	Yes	Treatment group Age=75.3±4.8; Sham group Age=75.3±2.2	L lateral prefrontal cortex; 10–20 system	Anode = F3	Cathode = Fp2	35	n/a	1.5 mA	15	Day 1 = Initial Learning Session only, Day 2 = Memory Reactivation + active tDCS or Sham Session, Day 3 and Day 30 = Retrieval Session only	Verbal Memory	Experimental Memory Task (Learning, Reactivation, Free Recall, and Recognition)	n/a	Active tDCS treatment enhanced Memory Recognition scores compared to Sham.
Case Reports and Clinical Case Series
Andrade, et al.; 2016.	AD diagnosis by NINCDSADRDA criteria, CDR = 1	1	tDCS; awake	None	No	Age=73	L DLPFC; 10–20 system	Anode = F3	Cathode = R supraorbital region	35	n/a	2 mA	30	10 sessions; 2 weeks	Global Cognition	ADAS-Cog	NPI, BDS, DAD	After treatment, ADAS-Cog, NPI, BDS, and DAD showed improvement compared to baseline
Bystad, et al.; 2016.	Early AD diagnosis, criteria not specified	1	tDCS; awake	None	No	Age=59	L temporal lobe; 10–20 system	Anode = T3	Cathode = FP2	not specified	n/a	2 mA	30	12 sessions; 6 days	Verbal Memory	CVLT-II, EEG	MMSE, TMT A, D-KEFS Word Fluency, WMS Attention Span, Clock-drawing test	After treatment, the CVLT-II and MMSE showed improvement compared to baseline.
Bystad, et al.; 2017.	Early-onset AD, Dubois criteria.	1	tDCS; awake, applied at home with help from family	None	No	Age=60	L temporal lobe; 10–20 system	Anode = T3	Cathode = FP2	not specified	n/a	2 mA	30	daily for 8 months	Memory, Visuospatial, Language, and Attention	RBANS		Overall the patient’s cognitive function remained stable over 8 months, with improvement in memory (immediate and delayed recall), and decline in visuospatial function.
Costa, et al.; 2017.	Possible AD diagnosis by NINCDS-ADRDA criteria, MMSE = 14.27	1	tDCS; awake	1 week of Sham was followed by treatment intervention	Yes	Age=67	R angular and supramarginal gyrus; 10–20 system	Anode = P6-CP6	Cathode = L supraorbital region	35	n/a	2 mA	30	5 sessions; 1 week	Language	BADA		After treatment there was a significant improvement in comprehension of verbs, compared to sham. This persisted for 2 weeks post-stimulation.
Gramegna, et al.; 2018.	Posterior cortical atrophy with AD diagnosis via CSF tau and a-beta	1	tDCS; awake	None	Cognitive rehab therapy preformed prior to initiation of tDCS	Age=58	L DLPFC; 10–20 system	Anode = F3	n/a	not specified	R shoulder	2 mA	20	20 sessions; 4 weeks; repeated for 2 separate cycles, total of 40 tDCS sessions	Executive function, fMRI	Stroop task while in the fMRI scanner	Complete NPS evaluation	The patient showed improvement on the Stroop task after cognitive training, which was maintained after the first and second tDCS cycle.
Mukku, et al.; 2018.	1 patient with an AD diagnosis, 1 patient with a LBD diagnosis	2	High Definition tDCS; awake	None	No	AD patient Age =; LBD patient Age=68	10–10 system	High Definition tDCS used five ring electrodes arranged on the scalp around the central Cathode	Cathode = CP5	ring electrode with outer radius 12 mm, inner radius 6 mm	n/a	2 mA	20	2 sessions per day, 10–20 sessions total; 5–10 days of treatment	Auditory Hallucinations	AHRS		Both the AD and LBD patient showed decrease frequency of auditory hallucinations on the AHRS and decreased acting out behavior.