The neurophysiological correlates of compassion

Abstract

This PhD thesis presents the application of compassion training to both healthy and clinically relevant populations (depression), using multi-modal techniques including fMRI, HRV (heart-rate variability), self-report, and behavioral measures. The aim of this program of research was to demonstrate how compassion training and self-reassurance (a compassionately-motivated relating style) can offset the deleterious impacts of self-criticism. Thus, providing novel insights into how we might be able to prevent and treat mental health disorders such as depression with compassion. The first chapter of this thesis provides an overview of the work presented within. The second chapter of this thesis comprises the literature review of the thesis, and is a systematic review and fMRI meta-analysis of compassion neuroimaging studies. Using a coordinates-based meta-analysis approach, this chapter ascertained the shared neural processes relevant to compassion, and demonstrated that these neural markers are shared with the empathy fMRI literature. Here, this analysis of sixteen fMRI studies revealed activation across seven broad regions, with the largest peaks localized to the Periaqueductal Grey, Anterior Insula, Anterior Cingulate, and Inferior Frontal Gyrus. Overall, this chapter identified a tendency for studies to operationalize compassion in one of three ways, as driven either ‘top-down’, ‘bottom-up’, or modified by contextual target factors (i.e., manipulating features such as perceived innocence versus guilt).The third chapter of this thesis reports the putative neurophysiological markers of Compassionate Mind Training (CMT). With fMRI, this chapter reports participants’ neural responses when confronted with disappointments (e.g., rejection, failure) using two fundamental self-regulatory styles, self-criticism and self-reassurance. Second, participant’s Heart-rate variability (HRV) – a marker of parasympathetic nervous system response – was assessed during compassion training, pre- and post- a two-week self-directed engagement period. fMRI data identified that cultivating self-compassion can downregulate neural markers of negative emotion, compared with self-criticism. Furthermore, cultivating compassion was shown to increase HRV, a marker of soothing, safety and self-regulation. Importantly, significant increases in HRV were only observed post the two-week training period, data that were explored further in chapter four. Chapter four outlines further analyses on the spatiotemporal nature of the HRV biosignal, and used techniques of visualization across timescales and time-series statistics to explore complexity associated with the HRV data collected in the previous chapter. Here, this chapter identified that the accuracy of representing HRV data is conserved across timescales. Furthermore, tests of stationarity and time-series distance measures, coupled with visualization of the 1-minute HRV bins, reveal the observed non-significant difference of HRV post-training (chapter three) could be driven from a raised physiological baseline after the two-week training.Chapter five extends an understanding of the neural markers of self-criticism, and particularly explores the influence of attachment styles on self-criticism at a neurobiological level. Here this chapter utilized data generated in chapter three to examine the relationship between self-reported attachment styles and neural markers of self-criticism using fMRI. First, this chapter identified that neural markers of visual mental imagery correlated with amygdala activity (threat response). And indeed, at greater levels of amygdala response, more securely attached individuals showed greater lingual gyrus activation, and more avoidantly attached individuals showed less lingual gyrus activation. In doing so, this chapter provides putative evidence for attachment styles as a focal moderator of neural markers of self-criticism, and highlights future fMRI research to consider attachment styles as a key covariate of neural response during compassion and criticism.Chapter six recognizes that self-reassurance, a compassionately motivated cognitive relating style, can down-regulate neural markers of negative emotion, and presents data that converge neural and self-report markers of reassurance. Here, this chapter identifies that participants with greater levels of perceived inadequacy exhibited greater neural activation within the medial prefrontal cortex (MPFC) and anterior insula (AI). Interestingly, no significant relationships were observed between brain activation (during self-reassurance) and self-report markers of hated and reassuring forms of self-criticism. In doing so, this chapter remarks on the potential for this scale to perhaps index increased negative emotion (AI) and mentalising (MPFC) during self-reassurance. This chapter suggests the need for future neuroimaging studies in compassion continue to explore aspects of the self that are liked versus disliked, in order to begin to probe constructs such as self-hatred, inadequacy and reassurance further.Chapter seven presents the world-first demonstration of HRV response during compassion training within a sample of severe depressive symptomology. Using the brief CMT method validated in healthy controls and presented in chapter three and four, these data replicate an increase in HRV during CMT for a sample of elevated depression symptomatology. Furthermore, cultivating compassion was shown to ‘shift’ this participant group to one of increased health, specifically by raising their HRV response above a clinical cut-off of low resting HRV, providing evidence of CMT’s significant impact on HRV. Last, Chapter eight reviews the overarching aims and findings of this thesis, and provides major conclusions, limitations, and future directions from this program of research.Taken together, this thesis is the first to demonstrate distinct neurophysiological markers of compassion training, particularly with the approaches outlined in Compassionate Mind Training, showing how compassion can reduce neural markers of negative emotion and threat, and facilitate increased HRV responses in populations of both health and depression. This work is also integrative of distinct methods, such as neurophysiology, self-report, and behaviour, and ultimately suggests the need for larger-scale randomized control trials, to further support CMT’s potential to help treat self-criticism and depression via modulation of neural and physiological markers during compassion.