Activity in the mouse visual cortex (V1) changes according to arousal level, but whether this is the case elsewhere in the visual circuit is unknown. The authors imaged calcium activity in retinal ganglion cell (RGC) terminals in the superior colliculus of mice placed on a treadmill to increase arousal. Whether under illuminated or dark conditions, treadmill running produced a change in activity (either an increase or decrease) in around half the terminals monitored. Moreover, activity of RGCs and downstream superior colliculus neurons also showed modulated responses depending on running speed, suggesting that arousal level influences activity from the retinal to V1.