PhD Oral Defence - Czarina Evangelista, Psychology
When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
After receiving a reward, motivation to obtain more is boosted. For example, a taste of chocolate drives me to want and consume more chocolate—sometimes to the point that I finish an entire bar! This phenomenon is called the priming effect of rewards. The priming effect of rewards has primarily been studied with electrical brain stimulation. Rats primed with brain stimulation have been shown to prefer brain stimulation over competing rewards. Additionally, they work harder for more rewarding brain stimulation. Although over half a century of research implicates dopamine transmission in reward and motivation, the priming effect may not depend on dopamine transmission.
This thesis investigated the priming effect of electrical brain stimulation and food and the role of dopamine transmission. First, expanding on the original work on the priming effect of electrical brain stimulation, we examined whether the priming effect depends on the strength and cost of reward. We showed that the priming effect of electrical brain stimulation is more likely to be observed when the reward intensity is high and the cost is low. Secondly, we investigated whether the priming effect generalizes to other rewards such as food. We demonstrated that food also elicits a priming effect. Lastly, it was studied whether dopamine transmission is necessary for the priming effect of electrical brain stimulation and food. We showed that the priming effect of those rewards persists following dopamine receptor antagonism.
Although dopamine transmission is important for reward and motivation, the present thesis provides evidence that it may not be essential for the priming effect. This emphasizes the need to reconsider and investigate the role of non-dopamine systems in reward and motivation.