Using light to establish habits in laboratory mice.

BACKGROUND AND AIMS: Perseverative behaviours are commonly assessed using operant paradigms in which rodents work for drugs or food under physiological deprivation, limiting translational relevance to some behavioural addictions. Here we validated an operant paradigm in which the acquired behaviour is driven neither by physiological needs nor novelty seeking. METHODS: Mice were trained to lever-press for green light. Exp.1 used a within-subjects design to examine lever discrimination and whether responding could be "satiated" by light preexposure. Exp.2 examined the necessity of instrumental contingency using a between-subjects design, with light delivery equated between contingent and non-contingent groups. Exp.3 replaced green light with dim red light producing less retinal photoreceptor excitation but comparable heat to assess non-photic cues. Exp.4 examined whether green light could affect food seeking under different motivational states. RESULTS: In Exp.1, green light supported lever discrimination. Among high responders, the satiation effect was modest (<15% reduction) and did not deter lever pressing. In Exp.2, instrumental contingency promoted response acquisition whereas random light delivery did not. In Exp.3, dim red light failed to sustain behaviour, producing ∼50% response decrement. In Exp.4, light potentiated food seeking under ad libitum feeding. DISCUSSION AND CONCLUSIONS: Response-contingent light serves as a reward to establish operant responding, which cannot be explained by alerting effects or thermal cues. Our study bridges the gap between animal models and findings from humans that coloured light may exacerbate smartphone use and that light therapy may reshape reward circuits in individuals with Internet gaming disorder symptoms [Li et al. (2026) Advanced Science 13:e14044].