In vivo functional near-infrared spectroscopy measures mood-modulated cerebral responses to a positive emotional stimulus in sheep

► This is the first study measuring affective brain states in unrestrained animals. ► Wireless functional near-infrared spectroscopy (fNIRS) assessed this brain activity. ► A novel in-vivo fNIRS device measured brain responses in freely moving sheep. ► Responses to a pleasurable grooming stimulus depended on the sheep's mood.