Mindfulness meditation for high anxiety individuals: psychological and attentional mechanisms and their role in therapeutic engagement and outcome

Background:
Symptoms of anxiety disorders are highly prevalent and are associated with subjective distress, diminished quality of life, and economic costs. Mindfulness-based practices and interventions have become increasingly adopted in Western societies and are efficacious in reducing symptoms of anxiety. However, little is currently known regarding their underlying mechanisms of action. While attentional processes have been implicated, limited empirical support has been derived from clinical populations. Furthermore, there is currently limited understanding of individual differences and psychological factors that influence attentional processes, mindfulness outcomes and engagement in self-directed mindfulness practice among anxious individuals. The current thesis describes a program of research intended to address these gaps in the literature to advance our understanding of how mindfulness may be optimised as a treatment option for individuals experiencing symptoms of anxiety.
Method:
The present thesis includes two systematic reviews containing meta-analyses to examine the effects and associated predictors, mediators, and moderators of acute mindfulness induction (1) and longer-term mindfulness training (2) on clinical outcomes among individuals experiencing symptoms of generalised anxiety. The thesis also includes three empirical studies to examine (1) psychological predictors of attentional bias to threat (ABT; i.e., the tendency to preferentially attend to threat-related information) using behavioural tasks, (2) the influence of trait anxiety, trait mindfulness and self-reported mindfulness experience on the executive control of attention using a behavioural task and event-related potentials (ERPs), and (3) psychological predictors of engagement in, and outcomes following, a two-week intervention involving self-directed use of a mindfulness app among individuals experiencing high levels of generalised anxiety. Empirical studies (1) and (2) involved high and low trait anxiety sub-samples to examine group differences on measures. In the empirical studies, ABT was measured using dot-probe, flanker (1) and Stroop (3) tasks with emotional stimuli, while executive control attention processes were measured using a hybrid flanker go/nogo task (2).
Results:
The meta-analysis from the first systematic review showed that mindfulness induction reduced state anxiety and increased state mindfulness in high anxiety participants, with medium and large effects, respectively, when compared with non-therapeutic control conditions. The meta-analysis from the second systematic review showed that mindfulness training reduced anxiety symptoms in Generalised Anxiety Disorder with large effect when compared to inactive/non-specified controls, and a narrative review suggested increased functioning of brain regions implicated in attention. While there was limited literature showing improvement of attentional processes in either review, changes in aspects of state and trait mindfulness were found to mediate anxiety reduction following mindfulness induction and training, respectively, in anxious individuals. In empirical Studies 1 and 3, limited replication of behavioural ABT was found in high anxiety participants in response to threat-related emotional stimuli. However, in Study 1, a sub-sample with high relative to low trait anxiety showed overall slowed performance on a flanker task regardless of stimulus valence, and among the whole sample, facets of trait mindfulness and personality were associated with ABT scores. In Study 2, high relative to low trait anxiety sub-samples showed differences on ERP measures (N2 and P3 amplitude) in a non-emotional flanker go/nogo task, suggesting some evidence of inefficient and disrupted executive control processes. In addition, among the whole sample, lower P3 amplitude on high load trials was associated with lower mindfulness experience and higher trait anxiety. Finally, in Study 3, following a two-week, self-directed, mindfulness intervention, participants experiencing high levels of generalised anxiety showed moderate-large reductions in anxiety, worry, depression, and stress, with almost half of the sample showing a clinically reliable reduction in generalised anxiety symptoms. Furthermore, while higher perceived behavioural control was associated with greater app engagement (days of use), higher perfectionism and higher trait mindfulness (non-judgement) were associated with lower engagement. Additionally, a history of lifetime mindfulness experience and higher ABT scores were associated with greater reductions in generalised anxiety symptoms from pre- to post-intervention.
Conclusions:
The findings support the use of mindfulness induction, manualised training, and app-based, self-directed practice for generalised anxiety symptoms and suggest that aspects of state/trait mindfulness and attention play a role in symptom reduction. The findings highlight difficulties with the replication of behavioural ABT in anxious individuals and indicate that ERP measures of attention may be more informative in assessing the effects of mindfulness intervention on attentional processes among anxious individuals in future randomised controlled trials. Finally, this work indicates potential psychological factors that may impede engagement in, and influence outcomes following, brief, app-based mindfulness for anxious individuals.