Brain mechanisms underlying option generation for behaviour

This thesis examines the highly interlinked fields of voluntary action, apathy and option generation. Substantial research have now implicated the medial frontal cortex in voluntary actions, but the exact roles of each region remain unclear. Seeking clarity on this is important because the lack of self-generated behaviour is characteristic of apathy, a debilitating condition prevalent in neurodegenerative diseases and occurring to varying degrees in healthy individuals. Unfortunately, the conceptualization of apathy is currently unclear. Proposals of its underlying cognitive mechanisms have also mostly focused on deficits in selecting between options and learning outcomes during feedback. Intriguingly, the possibility that an inability to self-generate options may contribute to apathy has never been examined. This is because neuroscientific research on option generation is sparse. Here, a major contribution was the advancement of our understanding of option generation for behaviour. As there was no suitable objective measure available in the current literature, a simple, quantitative and culture-free task to assess option generation was first developed. The task was then administered to patients with Parkinson‖s disease and utilised in two pharmacological studies of dopamine agonist (cabergoline) and antagonist (haloperidol). These provided the first direct evidence that dopamine modulates option generation for behaviour in humans, specifically in the aspects of fluency (generating many options) and uniqueness (how different each option is from others). The ability to generate options was also found to associate with apathy in the healthy population. Besides that, the multidimensional structure of apathy was examined via the development and rigorous validation of a new questionnaire known as the Apathy Motivation Index. Finally, a functional neuroimaging experiment in healthy individuals revealed that the pre-supplementary motor area plays a key role in planning during volitional decisions of what action to execute. Together, these findings have provided new insights and point to new directions for future work in this field.