Abstract
Meditation is an ancient endeavour. Presently, besides religious practice, it forms the basis for a number of clinical and non-clinical interventions. Despite this, much is yet to be understood about the neural mechanisms underpinning it. The goal of this thesis is to develop, test and refine a theory – cortico-striatal feedback-loop theory (CSFLT) – which proposes that attentional regulation influences reinforcement learning and feedback processing via alteration of striatal dopaminergic signalling.
Using behavioural, electrophysiological, and pharmacological methods, I will test two predictions from CSFLT. First, that attentional regulation practices such as focused attention meditation (FAM) or dysregulation practices such as media-multitasking (MM) will be respectively associated with positively or negatively biased reinforcement learning and feedback processing characteristics. Second, that these differences in reinforcement learning and feedback processing are respectively due to elevated or reduced tonic dopamine levels in the striatum.
I will show that experienced meditators exhibit positively biased reinforcement learning, driven in large part by reduced sensitivity to negatively valenced feedback. I will also show that media multitasking is associated with slower response speed on the flanker task, and that this in turn is associated with poorer ability to learn from positively valenced feedback. I present findings from a longitudinal study of FAM where I report that FAM causes participants to improve their executive attention, and flanker response speed. The improvement in flanker response speed is also associated with an improvement in positive reinforcement learning and a more negative feedback related negativity (FRN) to positive feedback. Finally, I use the dopaminergic prodrug cocareldopa (levodopa and carbidopa) to show that tonic dopamine is not the cause of changes in reinforcement learning and feedback processing due to FAM. Rather, the findings are consistent with a mechanism that begins with enhanced striatal D1 signalling and, with increasing meditation practice, results in reduced striatal D2 sensitivity. These findings have important implications for our understanding of the mechanisms underpinning FAM and also point to the possibility that FAM could be used to improve disordered reward processing.