Development of a non-invasive novel individual marmoset holder for evaluation by awake functional magnetic resonance brain imaging

Background: Although functional MRI (fMRI) in awake marmosets (Callithrix jacchus) is fascinating for functional brain mapping and evaluation of brain disease models, it is difficult to launch awake fMRI on scanners with less than 15 cm of bore size. A universal marmoset holder for the small-bore size MRI was designed, and evaluated whether this holder could conduct auditory stimulation fMRI in the awake state. New Method: The marmoset holder was designed with an outer diameter of 71.9 mm. A holder was designed to allow adjustment according to the individual head shape, enabling to use the holder universally. An awake fMRI study of auditory response was conducted to evaluate the practicality of the new holder. Whole-brain activation was investigated when marmosets heard the marmoset social communication phee call, an artificial tone sound, music (bossa nova), and reversed of those. Results: The prefrontal cortex was significantly activated in response to phee calls, whereas only the auditory cortex was activated in response to pure tones. In response to bossa nova, visual and auditory cortices of the marmosets were activated. In contrast, the auditory response was decreased when marmosets heard phee calls and bossa nova music played backward. Their stimulus-specific responses indicated they perceived and differentiated sound characteristics in the fMRI environment. Comparison with Existing Methods: A holder does not require surgical intervention or custom-made helmet to minimize head movement in small space. Conclusion: Our newly developed holder made it possible to perform longitudinal fMRI experiments on multiple marmosets in a less invasive manner. ### Competing Interest Statement The authors have declared no competing interest.