Table 1.

Characteristics of the included studies in the systematic review and meta-analysis.

References	Design	Number of patients	Male/female ratio	Age	MMSE of the patients	Disease severity	Medication (add-on-therapy)	DBS location	Cognitive assessment	Cognitive outcome
Sankar et al. (2015)	Case-control	6	4/2	60.7 ± 6.1	22.3 ± 4.5	Mild to moderate	Cholinesterase inhibitors	Fornix	MMSE, ADAS-cog	Deterioration of cognitive function
Baldermann et al. (2018)	Pre-post design	10	4/6	66.9 ± 4.3	18.3 ± 3.8	Mild to moderate	–	NBM	MMSE, ADAS-cog, ADAS-mem	Improvement of cognitive outcomes in less-advanced disease
Leoutsakos et al. (2018)	Phase I and II RCT	42	–	Range: 45–85	–	Mild	Cholinesterase inhibitors	Fornix	ADAS-cog, CDRsb, CVLT-II, NPI	A possible cognitive benefit among older (>65) participants
Scharre et al. (2018)	Case-control	3	–	62.3 ± 11.8	22.67 ± 0.72	Mild to moderate	–	VC/VS	CDR	Less decline in CDRsb
Mao et al. (2018)	Pre-post design	5	2/3	59 ± 1.79	2.4 ± 1.15	Severe	Cholinesterase inhibitors, Chinese medication	Fornix	MMSE, MoCA, CDR	Improvement in some cognitive aspects

RCT, randomized clinical trial; NBM, nucleus basalis of Meynert; MMSE, mini-mental state examination; ADAS, Alzheimer's disease assessment scale; CDR, clinical dementia rating; DBS, deep brain stimulation; TMT, trail making test; MoCA, Montreal cognitive assessment; VC/VS, the ventral capsule/ventral striatum.