Sweet Touch: The effect of glucose on psychphysiological relaxation in response to a standardized massage

Background. Hyperglycemia affects cardiac activity at basal states (Paolisso et al., 2000, 1997), yet its effect on cardiac reactivity in response to environmental changes has not been investigated extensively. In a previous experiment, we found evidence for an amplification of the physiological response to slow paced breathing following sugar ingestion (Meier et al., 2022). In an attempt to replicate and extend these findings, we study the effect of glucose ingestion on the autonomic relaxation response triggered by a soft-shoulder massage. In an exploratory manner, we will test whether the expected glucose-related amplification has a potential cognitive effect on sustained attention. Methods. Participants are randomly assigned to ingest a drink containing glucose, or pure water. After a waiting period, during which participants fill in questionnaires, they either receive a 10-min soft-shoulder massage or are allowed to rest. After the intervention, participants complete the d2 sustained attention test before a recovery period. Throughout the experiment, we repeatedly assess participants’ blood glucose concentration, blood pressure, and mood. Further, we monitor cardiorespiratory activity using electrocardiography (ECG) and impedance cardiography (ICG), and cortical activity using functional near-infrared spectroscopy (fNIRS*). Research question. With this preregistered analysis, we primarily plan to answer the research question: does glucose ingestion amplify autonomic reactivity to a massage? Further, we plan to explore whether this glucose-related amplification of autonomic reactivity has cognitive-behavioral consequences. This preregistration will thus focus on the effect of glucose intake on the parasympathetic and sympathetic responses to relaxation as induced by a massage, and on potential subsequent cognitive effects on sustained attention. * the fNIRS data are considered pilot data, as this is the first experiment in which we use fNIRS. If the data quality allows it, we will further explore cortical activation patterns in repone to our experimental manipulations.