Instrumentation for measuring oculomotor performance and plasticity in larval organisms

To study the genetic and developmental basis of sensorimotor processing, behavioral output must be quantified before the neural circuit dynamics can be investigated. The oculomotor system is ideal as it has been extensively utilized for quantitative analysis; however, no complete apparatus exists to both elicit and measure the eye movements in small genetic model organisms in real time. Instrumentation designed for much larger animals must be scaled to accommodate animals only a few millimeters in length, while accurately quantifying the motion of the minuscule eyes. To this end, a video microscope and optokinetic drum were mounted on a miniature, motorized vestibular turntable, servo-controlled with velocity and position feedback and capable of producing sinusoidal motion or position triangles with latencies less than 0.10 s and accelerations greater than 1000°/s². The optokinetic drum, also feedback controlled, accommodated a wide range of spatial frequencies that could be nested concentrically to provide visual stimuli for both monocular and binocular testing. Larval and juvenile Xenopus, zebrafish, goldfish, and medaka were embedded in agarose with the head free, allowing unrestricted eye movements and normal respiration. Infrared transillumination permitted video imaging of eye movements in either light or dark. Video images were computer processed in real-time (60 Hz), producing accurate (±0.1°) eye position measurements that, in turn, could be utilized in real-time for visuomotor plasticity paradigms. This instrumentation permits high resolution ontogenetic analysis of oculomotor function in small animals as illustrated for larval zebrafish (5 to 35 dpf).