Vagus Nerve Stimulation as a Gateway to Interoception

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2025-01-11 12:30:08

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The last two decades have seen a growing interest in the study of interoception. Interoception can be understood as a hierarchical phenomenon, referring to the body-to-brain communication of internal signals, their sensing, encoding, and representation in the brain, influence on other cognitive and affective processes, and their conscious perception. Interoceptive signals have been notoriously challenging to manipulate in experimental settings. Here, we propose that this can be achieved through electrical stimulation of the vagus nerve (either in an invasive or non-invasive fashion). The vagus nerve is the main pathway for conveying information about the internal condition of the body to the brain. Despite its intrinsic involvement in interoception, surprisingly little research in the field has used Vagus Nerve Stimulation to explicitly modulate bodily signals. Here, we review a range of cognitive, affective and clinical research using Vagus Nerve Stimulation, showing that it can be applied to the study of interoception at each level of its hierarchy. This could have considerable implications for our understanding of the interoceptive dimension of cognition and affect in both health and disease, and lead to development of new therapeutic tools.

Interoception pertains to receiving, encoding, and representation of internal bodily signals in the brain, as well as their perception (Cameron, 2001; Craig, 2002; Critchley et al., 2004). Through interoception we know when our heart is beating fast, when we need to take a deep breath, and when we are hungry, thirsty, hot, cold, nauseous, tired, or alert. It encompasses both the non-conscious bodily signals themselves and our conscious perception of them. Growing research has shown interoception not only to be crucial for homeostasis and allostasis (acute change to achieve homeostasis), but also central in a range of cognitive and emotional processes, including memory, decision-making, emotional processing, social interactions, and even consciousness, body ownership and a sense of self (Critchley et al., 2001; Dunn et al., 2010; Shah et al., 2017; Berntson et al., 2018; Critchley and Garfinkel, 2018). By their nature, internal bodily processes are notoriously difficult to manipulate in experimental settings. The vagus nerve, the main cranial nerve in the human body known to be central in relaying visceral signals to the brain, is naturally implicated in interoception (Critchley and Harrison, 2013; Quadt et al., 2019; Yoris et al., 2019). Yet surprisingly little research in this area has used vagus nerve stimulation (VNS) to modulate bodily signaling. So far, to the best of our knowledge, only one recent study has explicitly related VNS to interoception (Villani et al., 2019). Here, we review the accumulated cognitive and clinical research on VNS and propose that this technique can indeed be used to modulate a wide range of interoception-related processes.