The neuromodulatory effects of transcutaneous vagus nerve stimulation: a replication

Non‐invasive vagus nerve stimulation and the motivation to work for rewards: A replication of Neuser et al. (2020, Nature Communications)

“…Several recent taVNS studies have not managed to replicate the effects of invasive VNS on psychophysiological measures such as pupil size and P300 amplitude, reporting null effects instead (Burger et al., 2020; D'Agostini et al., 2022; Gadeyne et al., 2022; Keute et al., 2019; Warren et al., 2019). In the present work and another replication attempt (Lloyd et al., 2023), we find that even the results of high‐profile taVNS studies can be difficult to replicate. Parametric exploration of tVNS stimulation parameters (D'Agostini et al., 2023; Urbin et al., 2021) and pre‐registration, to combat p ‐hacking and publication bias (Munafò et al., 2017), may help this nascent field of inquiry to overcome these challenges.…”

“…This assumption is based on animal studies that have found that invasive VNS increases the firing rate of locus coeruleus neurons and increases extracellular norepinephrine levels (e.g., Dorr & Debonnel, 2006; Hassert et al., 2004; Raedt et al., 2011). However, the evidence for an effect of taVNS on non‐invasive physiological markers of noradrenergic activity is mixed, with some studies finding positive evidence (Giraudier et al., 2022; Lloyd et al., 2023; Sharon et al., 2021; Ventura‐Bort et al., 2018) and other studies finding negative evidence (Burger et al., 2020; D'Agostini et al., 2022; Keute et al., 2019; Warren et al., 2019)—especially studies using the relatively long on/off stimulation cycles of the taVNS device most often used in laboratory experiments (NEMOS®, Cerbomed GmbH, Erlangen, Germany). Positive findings of laboratory taVNS experiments with long on/off cycles or continuous stimulation, especially those using relatively low stimulation intensities (e.g., 0.5 mA), therefore warrant scrutiny, for example using direct replication studies.…”