Role of the circadian clock in motivation for a reward

AGOSTINO P.V.

Workshop; Neuroscience & Philosophy meeting; 2023

The circadian system regulates behavioral and physiological processes, including the response to natural and drug rewards. In mammals, the most potent synchronizer is the light/dark cycle, adjusting the internal clock to the 24-h external rhythm. In addition, food works as an important non-photic synchronizer. Chronic disruption of the circadian system caused by unsteady synchronization with light-dark schedules, such as advancing chronic jet lag (CJL), leads to adverse physiological effects and pathologies, and is linked with changes in mood and depressive behaviors in humans and rodent models.Motivation refers to the internal and external factors that drive individuals to act or behave in a certain way. Rewards, on the other hand, are incentives or outcomes that individuals receive as a result of their actions. The motivation for a reward arises from the desire to attain or experience the benefits associated with it. Motivation and reward-related behaviors are thought to be comprised of different components, such as the “liking” or hedonic component and the “wanting” or incentive salience component. From a philosophical point of view, motivation for a reward can be understood through hedonism, which posits that individuals are primarily motivated by the pursuit of pleasure and the avoidance of pain. According to this perspective, rewards serve as stimuli that generate positive emotions and satisfaction, ultimately driving individuals to engage in certain behaviors. Motivation can also be explored through other philosophical perspectives, such as utilitarianism, deontological ethics and virtue ethics.Our work consists in the study of motivation behavior in animal models (mice) to understand the role of the circadian system in regulating motivation and other mood-related behaviors. We have evidence of a circadian modulation of motivation for food reward in mice, which is unaffected by aging. We have also characterized motivation under two different disruptions of the circadian system: 1) When food is the main synchronizer and it is available only in the inactive phase of the rest/activity rhythm (by a time-restricted feeding protocol, TRF), and 2) When chronic phase advances in the light/dark cycle (by a chronic jet lag protocol, CJL) cause circadian alterations similar to time zone changes or shift-work. Our findings provide support for the hypothesis that the chronic disruption of the circadian organization may lead to, or aggravate, abnormal functioning in mood-related behaviors and increase the risk of lack of motivation and depression.Together, these findings contribute to gaining knowledge in potential mechanisms of circadian modulation of motivational states in order to improve treatment related to psychiatric disorders or drugs of abuse.