Fig. 1: Magnetic voluntary head-fixation system.

A The core of the system is the head plate with three ball bearings and three bearings of the Kelvin kinematic coupling. The 3-point cone, groove, and flat bearings non-redundantly constrain the six degrees of freedom of the head plate. B Photograph of the bearing system showing interface with head plate (white, wireframe). The brass objective protector prevents the animal from touching the front aperture of the objective while not occluding the optical excitation or emission. The magnet and adjuster are shown for the flat bearing only, two other magnets and adjustment screws sit behind the cone and groove bearing. C First and tenth images of a fluorescent bead sample taken during in vitro testing of kinematic registration and the bead displacements in x and y for all insertions (n = 50) during the test. D A microprism attached to the bearing system allows the translation of sample z-motion to imaging plane x-motion. The bead displacements in x and z are shown for all insertions (n = 50) of the test.