Many vision studies in non-human primates require head immobilization to accurately measure eye movements and record neural signals. Researchers typically use surgically implanted head restraints for this purpose, however, surgically implanted headposts come with risks and limitations. First, headposts are prone to infection and may fail over time. Second, their footprint on the skull is large and impose surgical and experimental constraints. Third, headposts do not enable experimental designs that require voluntary animal engagement, such as cage-side data collection. Several non-invasive head immobilization systems (NHIS) have been developed but have not been widely adopted, perhaps because they are difficult to construct and modify for diverse research applications. We developed a novel 3D-printed NHIS for macaque monkeys which is easy to produce and customize. We used a CT scan of a monkey’s head and custom software (FLoRIN) to design a 3D-printable helmet with cutouts for eye-tracking, reward delivery, and physiology hardware. The design features a backpiece that can be optionally used to fully restrain the head. We validated the NHIS’s efficacy by comparing eye-tracking measurements recorded from a helmet-stabilized monkey with a headpost-immobilized monkey. The helmet-stabilized monkey was trained to voluntarily place its head in the helmet and fixate on visual targets presented on the screen up to 10° eccentricity for liquid reward. The helmet-stabilized monkey showed high fixational precision (0.23±0.11°) and accuracy (0.47±0.21°) without requiring the use of full restraint via the backpiece, comparable to the precision (0.12±0.22°) and accuracy (0.41±0.27°) of the headpost-immobilized monkey. These results show suitable eye-tracking accuracy for broad use of our NHIS in visual studies. Moreover, the 3D-printed nature of the system improves the ease of construction and modification over previous NHIS. Taken together, the design could facilitate a move away from surgically implanted head-immobilization systems.
Acknowledgements: NIMH Intramural Research Training Award (IRTA) Fellowship Program; NIMH Grant ZIAMH002958