Abstract
Previous clinical research found that invasive vagus nerve stimulation (VNS) enhanced word recognition memory in epileptic patients, an effect assumed to be related to the activation of brainstem arousal systems. In this study, we applied non-invasive transcutaneous auricular VNS (tVNS) to replicate and extend the previous work. Using a single-blind, randomized, between-subject design, 60 healthy volunteers received active or sham stimulation during a lexical decision task, in which emotional and neutral stimuli were classified as words or non-words. In a subsequent recognition memory task (1 day after stimulation), participants' memory performance on these words and their subjective memory confidence were tested. Salivary alpha-amylase (sAA) levels, a putative indirect measure of central noradrenergic activation, were also measured before and after stimulation. During encoding, pleasant words were more accurately detected than neutral and unpleasant words. However, no tVNS effects were observed on task performance or on overall sAA level changes. tVNS also did not modulate overall recognition memory, which was particularly enhanced for pleasant emotional words. However, when hit rates were split based on confidence ratings reflecting familiarity- and recollection-based memory, higher recollection-based memory performance (irrespective of emotional category) was observed during active stimulation than during sham stimulation. To summarize, we replicated prior findings of enhanced processing and memory for emotional (pleasant) words. Whereas tVNS showed no effects on word processing, subtle effects on recollection-based memory performance emerged, which may indicate that tVNS facilitates hippocampus-mediated consolidation processes.
Highlights
One of the core aspects of adaptive behavior is the detection and remembrance of emotionally salient information
We investigated the impact of transcutaneous auricular VNS (tVNS) on emotional word processing and later recognition memory
TVNS showed no effects on word processing and overall emotional recognition memory performance
Summary
One of the core aspects of adaptive behavior is the detection and remembrance of emotionally salient information. For lexical material, an overall advantage for emotional (pleasant and unpleasant) words is consistently reported in lexical decision and reading tasks (Eviatar and Zaidel, 1991; Ortigue et al, 2004; Kanske and Kotz, 2007; Herbert et al, 2008; Schacht and Sommer, 2009; Scott et al, 2009; for a review see Kissler et al, 2009) These emotional benefits in attention may further influence memory formation and consolidation (Dolcos and Cabeza, 2002; Kensinger, 2009; Lang and Bradley, 2010), during sleep (Wagner et al, 2006; Payne et al, 2008; Nishida et al, 2009), leading to increased memory retrieval for emotionally relevant compared with neutral information (Bradley et al, 1992; Weymar and Hamm, 2013; Dolcos et al, 2020b). A particular characteristic of the mnemonic advantage for emotionally relevant material is that it seems to be sensitive to arousal (exciting vs. calming) rather than valence (pleasant vs. unpleasant), leading to prioritized perception and memory of emotionally (pleasant and unpleasant) arousing information at the expense of neutral, less-relevant information (Mather and Sutherland, 2011; Mather et al, 2016)
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