Abstract
In this work, we extend to the multivariate case the classical correlation analysis used in the field of network physiology to probe dynamic interactions between organ systems in the human body. To this end, we define different correlation-based measures of the multivariate interaction (MI) within and between the brain and body subnetworks of the human physiological network, represented, respectively, by the time series of δ, θ, α, and β electroencephalographic (EEG) wave amplitudes, and of heart rate, respiration amplitude, and pulse arrival time (PAT) variability (η, ρ, π). MI is computed: (i) considering all variables in the two subnetworks to evaluate overall brain–body interactions; (ii) focusing on a single target variable and dissecting its global interaction with all other variables into contributions arising from the same subnetwork and from the other subnetwork; and (iii) considering two variables conditioned to all the others to infer the network topology. The framework is applied to the time series measured from the EEG, electrocardiographic (ECG), respiration, and blood volume pulse (BVP) signals recorded synchronously via wearable sensors in a group of healthy subjects monitored at rest and during mental arithmetic and sustained attention tasks. We find that the human physiological network is highly connected, with predominance of the links internal of each subnetwork (mainly η−ρ and δ−θ, θ−α, α−β), but also statistically significant interactions between the two subnetworks (mainly η−β and η−δ). MI values are often spatially heterogeneous across the scalp and are modulated by the physiological state, as indicated by the decrease of cardiorespiratory interactions during sustained attention and by the increase of brain–heart interactions and of brain–brain interactions at the frontal scalp regions during mental arithmetic. These findings illustrate the complex and multi-faceted structure of interactions manifested within and between different physiological systems and subsystems across different levels of mental stress.
Highlights
Network physiology is a novel research field describing the human organism as an integrated network in which nodes correspond to the organs and edges map organ interactions (Bashan et al, 2012; Bartsch et al, 2015; Ivanov et al, 2016)
It has been shown that both mental load and physiological stress produce repeatable variations in the brain activity (Gevins et al, 1998; Berka et al, 2007; Al-shargie et al, 2018), and in the dynamic control of the cardiovascular function and heart rate variability (HRV) (Petrowski et al, 2017; Kim et al, 2018; Pernice et al, 2018, 2019a); these effects can be of clinical relevance as they can increase the risk of heart attacks and stroke (Steptoe and Kivimäki, 2013; Al-Shargie et al, 2016)
The E4 wristband provided by Empatica (Milano, Italy) with a photoplethysmographic (PPG) sensor has been used for blood volume pulse (BVP) signal
Summary
Network physiology is a novel research field describing the human organism as an integrated network in which nodes correspond to the organs and edges map organ interactions (Bashan et al, 2012; Bartsch et al, 2015; Ivanov et al, 2016). Among the variety of organ system interactions, brain– heart interactions play an important role since they underlie the activity of the autonomic nervous system (ANS) and the central nervous system (CNS), which are strictly interconnected through anatomical and functional links and influence each other continuously (Thayer et al, 2012; Beissner et al, 2013; Silvani et al, 2016) Effects of such interactions have practical importance, as, for instance, cerebral diseases like ischemic stroke and transient ischemic attacks can be due to cardiac arrhythmias such as atrial fibrillation (Marini et al, 2005; Buchwald et al, 2016). Besides the interplay between brain and heart, the network of interactions sub-serving the regulation of the homeostatic function encompasses other physiological rhythms, such as the respiratory drive (Pfurtscheller et al, 2019; Javorka et al, 2020), the cardiovascular and baroreflex functions (Krohova et al, 2019, 2020; Ringwood and BagnallHare, 2020), and other less studied but significant vital signs, e.g., including muscular and ocular activities (Ivanov et al, 2017; Boonstra et al, 2019)
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