Statistical analysis on characteristic whisker movements observed in reward processing

Internal states of the brain can be often reflected as facial expressions. However, how animals show their facial expression is largely unexplored. Here, we focus on mice and investigate whether their whisker movements could be a facial expression of their internal states related to reward processing. We trained three mice for an auditory association task and filmed their whiskers during the task performance after enough learning. We found that approximately 5-8 Hz periodic whisking was commonly observed during reward-associated Go cue presentation. Such whisking rarely occurred in No-Go cue trials or in Go cue trials where the mice were not motivated to get a reward. Furthermore, after acquiring a reward, the mice whisked with a more protracted set-point. Using machine learning, we could accurately indicate reward-anticipating and reward-acquiring trials only from whisker time plots. Our analyses suggest that mice exhibit stereotypic whisker movements as a part of orofacial movements related to reward anticipation and acquisition.