Titolo della tesi: From Gut to Cortex: Bottom-Up Measurament and Top-Down Modulation of Interoceptive Processes Across Bodily and Moral Domains
The present thesis aims to advance our understanding of interoception by addressing key conceptual and methodological gaps in both the measurement and modulation of internal bodily awareness. Specifically, it seeks to develop a novel, ecologically valid method for assessing gastric interoceptive accuracy via bottom-up, gradual, physiological perturbation, and to explore the causal role of the right anterior insula (rAI) in modulating interoception and morally relevant decision-making through top-down neuromodulation. Together, these approaches allow for a comprehensive investigation of how visceral signals are perceived, how they can be experimentally manipulated, and how they influence higher-order cognitive and social behavior.
In the first part of this thesis, I address a critical theoretical gap in the field: the lack of non-invasive paradigms for accurately assessing gastric interoception. While cardiac interoception has been extensively studied using established tools such as the Heartbeat Counting Task (Schandry, 1981), equivalent tools for the gastric domain remain underdeveloped. Existing paradigms, such as the Water Load Test-II (WLT-II; van Dyck et al., 2016), operationalize gastric interoceptive accuracy as the discrepancy between satiety and fullness. However, these may represent distinct constructs influenced by individual differences in perceptual thresholds. Moreover, the WLT-II provides only a single measurement point, limiting the ability to examine interoceptive performance across varying levels of gastric distension. Finally, the use of a fixed drinking modality may prompt reliance on exteroceptive cues or cognitive strategies, thereby reducing the validity of the interoceptive measure.
Drawing inspiration from prior approaches (e.g; van Dyck et al., 2016; G.-J. Wang et al., 2008) I present the multi-trial Water Load Test (mtWLT) to assesses interoceptive accuracy by gradually manipulating gastric fullness across multiple trials, with participants drinking water in incremental stages, while preserving the ecological advantages of the WLT-II and overcoming its conceptual and procedural limitations. The mtWLT involves progressive gastric distension across multiple drinking trials, each accompanied by ratings of fullness, satiety, nausea, discomfort, and thirst, as well as confidence judgments for assessing metacognitive awareness. Through randomized volumes and modalities of water ingestion, the task aims to minimize reliance on exteroceptive cues and anchors participants to visceral feedback. By comparing mtWLT performance with cardiac interoception and interoceptive sensitivity questionnaires, this part of the thesis establishes a novel bottom-up framework for measuring interoceptive accuracy specifically within the gastrointestinal axis.
In the second part, the thesis investigates the top-down modulation of interoceptive processing via non-invasive brain stimulation of the rAI, a central hub in the interoceptive network. While the rAI has been repeatedly implicated in interoceptive awareness, causal evidence remains scarce. Building on findings by Pollatos et al. (2016), we applied continuous theta burst stimulation (cTBS) to transiently inhibit rAI activity and observed its effects on cardiac interoceptive accuracy (Study 2a). In Study 2b, I extended this neuromodulatory approach to the domain of moral decision-making, examining whether top-down inhibition of interoceptive processes would moderate individuals’ reliance on internal bodily signals over external social cues, specifically, reputational risk, and favourable or unfavourable trials, when deciding whether to lie for personal gain. Participants completed the Temptation to Lie Card Game (TLCG; Azevedo et al., 2018; Panasiti et al., 2011, 2014, 2016).) under varying reputational conditions, following stimulation to the rAI, the right temporoparietal junction (rTPJ), and a sham control site. This design allowed us to test the hypothesis of whether interoception causally shapes social behavior and whether impairing the activity in the insula would enhance sensitivity to reputational risks by weakening internal self-monitoring.
Overall, this thesis aims to advance the theoretical understanding of interoception by introducing a novel bottom-up approach for assessing gastric interoceptive accuracy, and by investigating the causal, top-down role of the right anterior insula in bodily awareness and its modulatory role in social decision-making, particularly focusing on the behavioral implications of disrupted interoceptive processing in morally salient contexts. By integrating psychophysical and neuromodulatory methods, this work offers novel insights into how internal bodily signals are monitored, modulated, and used to navigate social environments.