INTRODUCTION: The superior colliculus (SC) is a midbrain structure essential for integrating visual information and initiating orienting behavior. Beyond its classical role in sensorimotor coordination, recent findings suggest that the SC modulates reward-related dopaminergic circuits. While lateralized SC projections to midbrain dopaminergic nuclei have been described in rats, the spatial organization of this influence remains largely unexplored.

AIM(S): This study aimed to develop a robust and spatially precise in vivo setup that enables the functional mapping of SC-driven visual input onto dopaminergic neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA).

METHOD(S): We designed a custom 3D-printed head-surrounding chamber for use with anesthetised, stereotaxically mounted Sprague-Dawley rats. The chamber houses an 8×32 LED matrix programmed via Arduino to emit 10-ms light flashes at defined spatial coordinates, allowing targeted stimulation of specific retinal regions. The system is optimized for concurrent extracellular single-unit recordings in SNc and VTA using high-impedance glass electrodes.

RESULTS: We successfully developed and validated a stable and reproducible experimental setup suitable for precise visuo-electrophysiological studies in the rat midbrain. The system enables fine control over the spatial parameters of visual stimulation and allows for stable single-neuron recordings. Pilot tests suggest the potential to resolve topographic patterns of SC-driven visual input, which will be systematically tested in the upcoming recording experiments.

CONCLUSIONS: Our setup enables high-resolution functional mapping of visual input to midbrain dopaminergic circuits in vivo. It lays the foundation for uncovering whether and how the SC exerts spatially organized control over reward-related structures, with relevance for understanding subcortical sensory-motivational integration.