TABLE 1.

Summary of vagus nerve stimulation (VNS) in humans comparing the effects of cervical and auricular stimulation.

References	Type of VNS	Task	Timing of VNS	Male (M)/Female (F) ratio (shown as %)		Subject condition	Effect of VNS
				SHAM (%)	VNS (%)
Klaming et al., 2022	tcVNS	Recognition	Before learning	53M/47F	73M/27F	Healthy adult	Fewer false negative errors in recognition task (p < 0.05)
Sun et al., 2017	dcVNS	Working memory	Before/during learning	N/A	60M/40F	Epileptic adult patients	Fewer errors in working memory task (OR = 0.63)
Clark et al., 1999	dcVNS	Recognition	After learning	N/A	Not reported	Epileptic adult patients	Improved memory retention in verbal memory task (p < 0.05)
Hoppe et al., 2001	dcVNS	Recognition	Random	N/A	72M/27F	Epileptic adult patients	No effect on verbal/figural learning tasks (p > 0.05)
McGlone et al., 2008	dcVNS	Memory Observation Questionnaire	Random	N/A	56M/44F	Epileptic adult patients	No effect on objective memory scores/memory complaints (p > 0.05)
Ghacibeh et al., 2006	dcVNS	Recall/Recognition	After learning or before recall/recognition	N/A	50M/50F	Epileptic adult patients	VNS after learning improved retention in verbal memory task (p < 0.01)
McIntire et al., 2021	tcVNS	Multi-tasking	Before/after task	85M/15F	80M/20F	Healthy sleep fatigued adults	Less fatigued induced decline (p < 0.05)
Mertens et al., 2022	dcVNS and taVNS	Recognition	After learning	N/A	33M/67F	Epileptic adult patients	No acute effect on word recognition task (p > 0.05)
Mertens et al., 2020	taVNS	Recognition	After learning	N/A	Younger = 49M/51F Older = 29M/70F	Healthy adults	No effect on recall or recognition (p > 0.05)
Jacobs et al., 2015	taVNS	Associative memory	During/after learning	N/A	50M/50F	Older adults	Higher correct hits in face-name task (p < 0.05)
Helmstaedter et al., 2001	dcVNS	Recognition	During testing	N/A	Not reported	Epileptic adult patients	Reversible decline in figural recognition (p < 0.05)

Experimental design parameters in clinical vagus nerve stimulation (VNS) studies investigating memory performance. Application of VNS in clinical studies was found to have varied success in improving memory in specific behavioral tasks. Experimental factors, including site of VNS application, timing of VNS administration in relation to task, and sex, may mediate efficacy of VNS-induced memory enhancement. Where available the proportion of male to female for the human subjects participating in the studies was expressed as a% [under male (M)/female (F) ratio]. dcVNS, direct cervical vagus nerve stimulation; taVNS, transcutaneous auricular vagus nerve stimulation.