Hewitt, Samuel R.C.;
(2025)
Neurocomputational mechanisms of effort and motivation over time.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Effort is a cost of doing things and motivation is the willingness to overcome it. I investigated the subjective, behavioural, computational and brain basis of motivation in humans. I focused on several factors which could drive changes in motivation over time. In the first study, I probed subjective motivation in children and show that it has a similar structure to adults. Like in adults, trait apathy in children is associated with depression and impulsivity. This study suggests that trait apathy emerges early in life which may have profound biopsychosocial consequences. Adults also vary in how much effort they are willing to make. However, studies of effort-based decision-making are overwhelmingly cross-sectional meaning that they cannot assess changes over time. This contrasts with the widespread intuition that motivation seems to change. In the second study, I found that subjective motivation fluctuates substantially over time and these fluctuations are associated with changes in choices. When people feel more motivated than normal, rewards appear more valuable, driving willingness to make effort. Learning and dopamine are further mechanisms which could drive changes in motivation over time. In the third study, I investigated the role of dopamine in learning about effort and deciding whether to do it. Using computational brain imaging, I tested whether learning signals about reward and effort were modulated by L-dopa (which boosts dopamine). Firstly, I showed that there are robust reward and effort learning signals in the human brain. Secondly, there were dissociable shifts in reward and effort learning on L-dopa. These were associated with changes in brain areas critical for learning. These results suggest that dopamine may shift learning toward effort when effort strongly determines rewards (as is often the case in the real world). This work provides new insights into several mechanisms which may drive changes in motivation over time.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Neurocomputational mechanisms of effort and motivation over time |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10205767 |
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