Effect of theta-transcranial alternating current stimulation on working memory performance among healthy adults: A systematic review and meta-analysis

Table 1 Characteristics of the included studies

Ref.	Study design	Target region	Duration	Frequency	Concurrent task	Task	Task modality
Alekseichuk et al[49], 2017	Within subject	Frontoparietal	18	6	Online	N-back	Spatial
Bender et al[35], 2019	Within subject	Parietal		4	Online	Delayed match-to-sample task	Spatial
Biel et al[24], 2022	Between-subject, within subject	Frontoparietal	14	6	Online	Delayed letter recognition task	Verbal
Chander et al[50], 2016	Between-subject	Frontoparietal	4	Personalized	Online	N-back	Verbal
Debnath et al[36], 2024	Within subject	Frontal	20	5	Online	Delayed match-to-sample task	Objective
Draaisma et al[34], 2022	Within subject	Frontoparietal	30	Personalized	Online	N-back	Objective
Jaušovec and Jaušovec[25], 2014	Within subject	Frontal, parietal	15	Personalized	Online	Visual-array comparison task	Objective
Jaušovec et al[33], 2014	Within subject	Frontal, parietal	15	Personalized	Online	N-back	Verbal
Jones et al[51], 2019	Within subject	Frontoparietal	15	4.5	Online	N-back	Objective
Kleinert et al[40], 2017	Within subject	Frontoparietal	26	5	Online	Delayed match-to-sample task	Spatial
Ociepka et al[42], 2024	Within subject	Parietal	20	5.5	Online	Antisaccade, recall, graph mapping task	Spatial
Pahor and Jaušovec[32], 2017	Within subject	Parietal, frontoparietal, frontal	15	Personalized	Offline	N-back	Verbal
Röhner et al[37], 2018	Within subject	Frontoparietal	15	6	Offline	N-back	Verbal
Tseng et al[41], 2018	Within subject	Parietal	22	6	Online	Change detection task	Spatial
Violante et al[30], 2017	Within subject	Frontoparietal	26.5	6	Online	N-back	Verbal
Wolinski et al[31], 2018	Within subject	Parietal	12	4	Online	Delayed match-to-sample task	Objective
Xiao et al[29], 2023	Within subject	Frontoparietal	20	6	Offline	Delayed match-to-sample task	Spatial
Yang et al[28], 2024	Within subject	Frontal	16	5	Offline	N-back	Spatial
Zeng et al[52], 2022	Between-subject	Frontal	20	8	Offline	N-back	Verbal
Zhang et al[53], 2022	Within subject	Frontoparietal	25	Personalized	Online	Spatial forward span task	Spatial
Zhang et al[38], 2022	Between-subject	Frontoparietal	15	6	Offline	N-back	Verbal

Table 2 N-back subgroup analyses

Covariables	Subgroups	Number of effect sizes	Hedges’ g	95%CI	I² (%)	τ²	P value
Study design							0.296
	Within-subject	33	0.260	0.136-0.386	57.20	0.079
	Between-subject	8	0.504	0.064-0.945	64.80	0.268
Target region							0.681
	Frontoparietal	18	0.324	0.096-0.552	72.50	0.181
	Parietal	9	0.200	-0.012 to 0.412	39.30	0.039
	Frontal	14	0.306	0.128-0.485	41.20	0.035
Frequency							0.001
	Fixed	15	0.608	0.336-0.881	72.30	0.204
	Personalized	26	0.133	0.039-0.227	11.70	< 0.001
Concurrent task							0.014
	Online	15	0.490	0.239-0.742	67.3	0.167
	Offline	20	0.153	0.057-0.250	36.80	0.004
Load							0.726
	1	4	0.532	-0.032 to 1.097	69.80	0.227
	2	18	0.274	0.041-0.508	73.60	0.192
	3	15	0.251	0.131-0.371	26.50	< 0.001
	4	2	0.549	0.005-1.094	21.60	0.033
	5	2	0.187	-0.283 to 0.657	0.00	0.000
Task modality							0.005
	Spatial	3	1.168	0.529-1.807	77.90	0.245
	Verbal	36	0.189	0.096-0.281	35.40	0.014
	Objective	2	0.405	0.143-0.666	0.00	0.000

CI: Confidence interval.

Table 3 Delayed match-to-sample task subgroup analyses

Covariables	Subgroups	Number of effect sizes	Hedges’ g	95%CI	I² (%)	τ²	P value
Study design							0.564
	Within-subject	15	0.092	-0.197 to 0.380	76.00	0.255
	Between-subject	2	-0.090	-0.636 to 0.456	0.00	0
Target region							0.012
	Frontoparietal	10	-0.082	-0.490 to 0.326	78.10	0.346
	Parietal	3	0.574	0.277-0.871	0.00	0
	Frontal	4	0.077	-0.173 to 0.328	0.00	0
Concurrent task							0.295
	Online	15	0.105	-0.185 to 0.395	75.40	0.252
	Offline	2	-0.168	-0.588 to 0.253	0.00	0
Task modality							0.433
	Spatial	7	0.005	-0.642 to 0.652	87.60	0.680
	Verbal	4	0.020	-0.241 to 0.280	0.00	0
	Objective	6	0.226	0.022-0.430	0.00	0

CI: Confidence interval.