Motivation and reward-seeking in dorsal raphe nucleus

Thesis

In this thesis, I investigate the role of the dorsal raphe nucleus (DRN) in reward-guided behaviour. DRN is an ancient part of the brainstem and an important source of serotonin in mammals, but fundamental aspects of its function remain elusive. Here, I present a combination of human and non-human primate experiments to argue that DRN controls changes in rewardseeking. In Ch.III, I use recently developed analysis techniques to show that monkeys exhibit motivation-states during a foraging-style behavioural task. These states shaped their baseline predisposition to pursue rewards, and were linked to the richness of the environment: a highmotivation state was occupied when the environment was rich with many high-value opportunities, and a low-motivation state was occupied when the environment was poor and low-value opportunities abounded. In Ch.IV, I show that distinctive patterns of DRN activity occurred when animals transitioned between these states. I then show that disrupting DRN with transcranial ultrasound stimulation reduced the frequency of motivation-state transitions and prevented animals from reconciling their motivation-state with the richness of the environment. Finally, in Ch.V I demonstrate that DRN has a similar role in the human brain. I show that human behaviour during a foraging-style task is characterised by temporally persistent behavioural policies, and that these policies were set according to the richness of the environment. DRN activity signalled changes in behavioural policy, but only for changes that were adaptive given the richness of the environment. Taken together, these experiments suggest that DRN has a conserved and causal role in reconciling general patterns of reward-seeking with general features of the environment. 

Authors: Priestley, L

• DOI: 10.5287/ora-nojev9kxq
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Cognitive neuroscience