3D-Printable Non-invasive Head Immobilization System for Non-Human Primates

Abstract

A critical contribution to understanding the primate brain is our ability to directly record, manipulate, or image the brain in awake, behaving monkeys. A challenge with carrying out these studies is that typically the monkeys head must be fixed in place. While non-invasive head immobilization systems (NHIS) have been demonstrated to be effective, they have not fully replaced the use of surgically applied headposts. Here, we introduce a novel NHIS, with an option for voluntary engagement, for macaques using a widely available resource: the 3D printer. We designed customized 3D-printable head-immobilization masks for monkeys and a docking system using standard CT scans and user-friendly open-source software packages (FLoRIN, Blender, Python). We examined the efficacy and stability of our mask system for collecting eye fixation data by measuring trial-by-trial gaze precision and accuracy in two mask-immobilized monkeys and three headposted monkeys, including a within-subjects comparison. Our results demonstrate that monkeys stabilized by the mask maintain gaze precision and accuracy comparable with their headposted counterparts. While the headpost outperformed the mask, the difference in precision was 0.03{degrees} of visual angle, and the difference in accuracy was less than 0.2{degrees}, well within the acceptable range for most use-cases. Our process allows for the production of 3D-printable masks based on CT or MRI scans with the flexibility to incorporate design modifications for experimental equipment and resizing, potentially serving as a promising and more easily accessible alternative to headposts and other NHISs for primate neuroscience research.