A self-adjusting head holder without ear-bars for guinea pigs

A self-adjusting head holder is designed to allow stable fixation and precise positioning (anterior–posterior, pitch, and roll) of guinea pig head in stereotaxic devices. These are achieved with no use of ear-bars. It is thus easy to use, preferable for studies of the auditory system, and for avoiding tissue damage of the ear in general. This head holder can accommodate various head sizes and is thus adapted for males and females of a large range of body weights, as confirmed for guinea pigs of 360–940 g. Moreover, this head holder is easy and cost-effective to manufacture, making it accessible for any lab. Here, we present background and mechanical rationale, the technical specifications, and step-by-step manufacturing instructions for the stainless-steel and the plastic MRI-compatible versions of our self-adjusting head holder.