A new type of mouse gaze shift is led by directed saccades

In these experiments, a camera recorded the left pupils of awake head-fixed mice while left or right stimuli were randomly presented in 7-12 s intervals. Each session (360 stimulus presentations) used one of four stimulation protocols: 1) whisker airpuff, 2) ear airpuff, 3) auditory-only airpuff, and 4) tactile-only whisker bar. Airpuff stimuli were generated using 3D-printed nozzles connected to compressed air gated by a solenoid. For whisker airpuffs, the nozzles were positioned beneath the mouse’s left and right whiskers. For ear airpuffs, the nozzles were directed at the ears. For auditory-only airpuffs, the nozzles were moved away from the mouse to avoid deflecting whiskers while maintaining the same azimuthal position. For tactile-only whisker stimulation, the whiskers were deflected along an axis parallel to whisking motion using an L-key attached to a stepper motor. Unless otherwise noted, pupil video data was collected at 50 Hz. DeepLabCut was used to extract the left and right edges of both the pupil and the corneal reflection of an IR LED. Angular eye position (E) was determined using the formula: E = arcsin((CR-P)/Rp), where CR is the position of the corneal reflection center, P is the position of the pupil center, and Rp (1.08 mm) is the estimated radius of rotation of the pupil. Saccades were defined as eye movements that exceeded 100°/s, were at least 2° in amplitude, and were not preceded by a saccade in the previous 100 ms. The initial positions and endpoints of saccades were defined as the first points at which saccade velocity rose above or fell below 50°/s, respectively. In the subset of experiments that examined the relationship between saccade amplitude and velocity and bilateral eye movements, both eyes were recorded at 200 Hz. In an additional subset of experiments, attempted head movements were measured using load cells (a.k.a., strain gauges). In a subset of experiments, optogenetic manipulations of SC were performed in conjunction with the whisker airpuff stimulation. Optogenetic illumination was delivered on a random 50% of trials using 1 s of illumination centered around airpuff onset. For optogenetic inactivation of SC neurons, AAV1.hSyn.eNpHR3.0 was injected in right SC. For subthreshold optogenetic stimulation of SC neurons, AAV1.CaMKIIa.hChR2(H134R)-EYFP was injected in right SC. To control for the effects of light and viral expression, AAV9.CaMKII.GCaMP6s was injected in SC of 4 wild-type mice.