TABLE 1.

Overview of study characteristics of this clinical study and previous research investigating the effect of VNS on memory performance.

	This study	Clark et al. (1999)	Jacobs et al. (2015)
Study design	Within-subjects	Within-subjects	Within-subjects
Study population	Healthy volunteers	Epilepsy patients	Healthy older volunteers
	young age group
	old age group
Sample size	65	10	30
	41 young age group
	24 old age group
Memory function	Immediate recall	Immediate recall Delayed recognition	Name–face association
	Delayed recognition	Delayed recognition
Device	tVNS (NEMOS)	Invasive VNS	tVNS (TENStem)
Stimulation parameters
Output current	According to threshold	0.5–1.5 mA	5 mA
Frequency	25 Hz	30 Hz	8 Hz
Pulse width	250 μs	500 μs	200 μs
Duration	30 s	30 s	17 min
Washout period	30 min	unknown	>7 days
Number of conditions	3 (tVNS, sham, control)	2 (VNS, sham)	2 (tVNS, sham)