Three-photon imaging of mouse brain structure and function through the intact skull

Optical imaging through the intact mouse skull is challenging because of skull-induced aberrations and scattering. We found that three-photon excitation provided improved optical sectioning compared with that obtained with two-photon excitation, even when we used the same excitation wavelength and imaging system. Here we demonstrate three-photon imaging of vasculature through the adult mouse skull at >500-μm depth, as well as GCaMP6s calcium imaging over weeks in cortical layers 2/3 and 4 in awake mice, with 8.5 frames per second and a field of view spanning hundreds of micrometers. Wang et al. demonstrate that the effects of aberrations and scattering caused by the mouse skull can be reduced with three-photon microscopy. Their approach allows structural and functional imaging of the brain through an intact skull.