Investigating the Biological Correlates of Affectivity in Healthy Subjects and Bipolar Disorder.

Affectivity is a fundamental dimension of subjective experience involving feelings and emotions, and it is related to interoception and autonomic activity, which have been mapped onto the brain’s insula and associated neural circuits. Alterations in affectivity represent a key feature of bipolar disorder. However, the relationship between physiological signals, brain activity, and affective alterations remains unclear.
This work aims to investigate and characterize the biological correlates of affectivity in healthy subjects and bipolar disorder. Firstly, we investigated the potential relationship between autonomic signals (electrodermal activity, pulse rate, and skin temperature) and intrinsic brain connectivity in healthy subjects. Secondly, we explored potential alterations of autonomic-related brain connectivity in bipolar disorder.
In the study in healthy subjects (n = 39), the autonomic signals, i.e., electrodermal activity, pulse rate, and skin temperature, were acquired by using a physiological monitoring device (EmbracePlus), while intrinsic brain connectivity was measured using resting-state functional magnetic resonance imaging (rs-fMRI). We found a robust and specific correlation between pulse rate and intrinsic connectivity of the insula.
In the preliminary study on bipolar disorder, based on the results of the study on healthy subjects, we explored potential alterations in intrinsic connectivity of the insula, by using rs-fMRI in manic (n = 38), depressed (n = 41), and euthymic (n = 30) patients, along with healthy controls (n = 122). The result showed that insula connectivity is reduced in bipolar disorder and, among bipolar patients, tends to be decreased in manic symptomatology and increased in depressed symptomatology.
In conclusion, this study highlights the critical relationship between the brain’s insula and autonomic signaling. The robust positive correlation between pulse rate and insula connectivity in healthy subjects, as well as the alteration of insula connectivity in bipolar disorder, may show the important role of the insula in affectivity and its alteration in psychiatric disorders. These findings contribute to a deeper understanding of the interplay between physiological signals and brain function, offering potential pathways for developing biomarkers and therapeutic targets in bipolar disorder.