Soft shoulder massage amplifies glucose-induced increases in medial prefrontal activity: a pilot study employing a neurovisceral integration perspective

Abstract

Glucose intake has a modulating effect on autonomic activity at rest, indicating shared central mechanisms in the regulation of glucose homeostasis and autonomic responses. However, it is still unclear how glucose influences vagal and neuronal activity in response to changing environmental demands. To address this question, we studied the effect of glucose consumption on parasympa- thetic, and medial prefrontal reactivity in response to regenerative processes. For this, we invited fasted, healthy adult participants (n = 62, age mean = 23.0 years, SD = 4.05, 69.4% female) to the laboratory. After the consumption of either water or a drink containing glucose, participants were randomly assigned to a soft shoulder massage or a resting control group. Throughout the experi- ment, we simultaneously monitored cardiac vagal activity, indexed by root mean square of suc- cessive differences (RMSSD), and changes in medial prefrontal activation, indexed by changes in O2Hb concentrations, via continuous electrocardiogram (ECG) and functional near-infrared spec- troscopy (fNIRS) recording. In contrast to previous findings, we could not replicate an amplifying effect of glucose consumption on the physiological relaxation response. While we did not find a positive association between changes in medial prefrontal O2Hb concentration and vagal reactivity to the relaxation intervention, findings from our exploratory analysis suggest that higher blood glucose availability is associated with increases in medial prefrontal oxygenation. We discuss the results in the context of the neurovisceral integration theory.