The helmet head restraint system: a viable solution for resting state fMRI in awake monkeys.

In monkey neuroimaging, head restraint is currently achieved via surgical implants. Eradicating such invasive head restraint from otherwise non-invasive monkey studies could represent a substantial progress in terms of Reduction and Refinement. Two non-invasive helmet-based methods are available but they are used exclusively by the pioneering research groups who designed them. In the absence of independent replication, they have had little impact in replacing the surgical implants. Here, we built a modified version of the helmet system proposed by Srihasam et al. (2010 NeuroImage, 51(1), 267-73) and tested it for resting state fMRI in awake monkeys. Extremely vulnerable to motion artifacts, resting state fMRI represents a decisive test for non-invasive head restraint systems. We compared two monkeys restrained with the helmet to one monkey with a surgically implanted head post using both a seed-based approach and an independent component analysis. Technically, the helmet system proved relatively easy to develop. Scientifically, although it allowed more extensive movements than the head post system, the helmet proved viable for resting state fMRI, in particular when combined with the independent component analysis that deals more effectively with movement-related noise than the seed-based approach. We also discuss the pros and cons of such device in light of the European Union new 2013 regulation on non-human primate research and its firm Reduction and Refinement requests.