Current neuroscientific theories propose a causal role of bodily signals for higher-order cognition (embodied cognition). The autonomic nervous system represents the principal channel through which the brain and the body interact; e.g., rigid pattern of thinking (perseverative cognition, PC) has been associated with autonomic inflexibility, indexed by reduced heart rate variability (HRV). In light of such reciprocal interaction, it has been hypothesized that reduced HRV may be a cause, rather than a consequence, of PC.
In order to study the nature of brain-heart interactions in the service of cognitive functions, the project adopts bottom-up (parasympathetic-to-brain) and top-down (brain-to-parasympathetic) approaches. The bottom-up approach is implemented by experimentally manipulating HRV (through baroreceptor stimulation) and measuring the associated resting state and event-related brain responses using fMRI as well as subjective and behavioral correlates of PC (Study 1). The top-down approach is implemented by manipulating the left dorsolateral prefrontal cortex (DLPFC) via non-invasive brain stimulation (repetitive Transcranial Magnetic Stimulation; rTMS) and measuring the associated modulation of HRV and the subjective and behavioral facets of PC (Study 2).
Given that baroreceptor stimulation increases HRV, in Study 1 we hypothesize that efficacious (versus sham) baroreceptor stimulation will turn off the neural and subjective experience of PC and induce a higher flexibility of brain function.
In Study 2, we will test whether facilitatory rTMS over DLPFC enhances parasympathetic activation (increase in HRV), which in turn should dampen the subjective and behavioral signatures of PC.
The expected results hold promise of theoretical and methodological advancements by clarifying the functional interactions between the autonomic system, brain activity and cognitive functions, which is of great interest for both clinical psychology and neuroscience.
In spite of the tremendous amount of work on the association between reduced HRV and perseverative cognition, to date no studies have tried to experimentally manipulate parasympathetic function with the aim to reduce the perseveration of thoughts. The study has the ambitious objective to go substantially beyond the current theoretical and methodological state of the art, by expanding the recent advances on our understanding of the role of brain-body and body-brain interactions and their influence on psychological and somatic health.
Methodological advancement
At the methodological level, the neural signatures of parasympathetic nervous system activity are becoming increasingly clear thanks to the technical progresses in MRI-compatible physiological monitoring (Critchley et al., 2011; Thayer et al., 2012). However, due to methodological difficulties and the need for interdisciplinary teams, the capability to simultaneously record (and manipulate) physiological signals in concomitance with brain imaging remains quite exclusive.
This innovative methodology is anticipated to yield fruitful results, with an impact on basic research, clinical psychology, and neuroscience. The group of researchers and PhD involved in the project has the necessary background expertise as well as access to all the technical facilities necessary to perform the studies.
Theoretical and clinical advancement
The study questions existing theories assuming that resting parasympathetic functioning has an impact on cognition. Second, the use of bottom-up (parasympathetic-to-brain) and top-down (brain-to-parasympathetic) approaches represents a unique inclusive methodology to elucidate brain-body pathways to perseverative thoughts, ultimately informing on the most cost-effective therapeutic application.
Considering that perseverative cognition is one of the most difficult symptoms to treat, our results may have important implications for therapy. For example, HRV biofeedback (Lehrer & Gevirtz, 2014) may result as a potentially promising therapy tool for psychiatric disorders like major depression and generalized anxiety in which perseverative cognition represents one of the most pervasive and distressing symptoms, associated with significant impairment in daily functioning.
Health-related advancement
Rumination and worry are not only implicated in psychological health, contributing to mood worsening and psychopathology, but are also considered to play an important role in somatic health. Even at nonclinical levels, perseverative cognition causes a ¿fight-or-flight¿ action tendency, followed by a cascade of biological events, starting in the brain and ending as peripheral stress responses such as increases in heart activity, blood pressure, and stress hormones like cortisol (Brosschot et al., 2006). Such prolonged physiological activation may lead to a generalized pathogenic state, ultimately contributing to the development of somatic disease. Indeed, rumination has been recently proposed as a mediator in the relationship between chronic stress and hypertension up to the point that it is considered the missing piece in the still unexplained association between mood and anxiety disorders and increased cardiovascular risk (Gerin et al., 2012).
Research that elucidates the mechanisms linking dysfunctional thoughts to the development of risk factors for cardiovascular risk is highly relevant for both prevention and therapy, if we consider that cardiovascular disease is the main cause of death in Europe, killing over 2 million people per year. Also, rumination and worry are dominant in depression and anxiety but to a lesser extent, they can be present in everybody's life with detrimental consequences on our health and sleep.
Some members of the research group (Hugo Critchley, Julian Thayer) are strongly represented in international health-related organizations, including NIH institutes, and will help to disseminate the results further via these connections. Understanding how to turn off perseverative thoughts has an important bearing on the psychological and physical well-being of the individual and may ultimately clarify an important part in the etiology of cardiovascular disease.