Event:

The operating mode of the visual system depends on behavioural states such as arousal. This dependence is seen both in primary visual cortex (V1) and in subcortical brain structures receiving direct retinal input. In my talk, I will show that modulation by behavioural state arises as early as in the output of the retina. We first measured activity in a region that receives retinal projections, the superficial superior colliculus (sSC), using two-photon imaging in head-fixed mice that were free to run on a treadmill. The level of arousal was gauged by running speed and pupil diameter. We found that activity in sSC neurons strongly depended on behavioural state. This dependence was not mediated by feedback inputs from V1 as it was immune to V1 inactivation. To test whether the modulation by behavioural state in the sSC was already present in the input from the retina, we used Neuropixels probes to record activity in the optic tract. We found some retinal axons whose activity significantly varied with arousal, even in darkness. To characterize these effects on a larger sample of retinal outputs, we imaged the activity of retinal boutons in sSC during behaviour. The activity of these boutons correlated with arousal as strongly as that of sSC neurons, and this correlation with arousal persisted during darkness. These results reveal a novel property of retinal function in mice, which could be observed only during behaviour: retinal outputs are modulated by behavioural state before they reach the rest of the brain.