In this research line, we took advantage of three-photon fluorescence microscopy (3PFM) to extend the access to neuronal activity information at deeper structures of the brain. Imaging with 3PFM will enable deeper and higher resolution imaging compared to two-photon or single-photon fluorescence microscopy. Longer excitation wavelengths reduce the tissue scattering and the higher-order nonlinear excitation increases the background suppression, thus overcoming the depth limit imposed by the signal-to-background ratio of TPFM. These properties allow to achieve hippocampal CA1 functional imaging at ~1 mm depth within an intact mouse brain (Ouzounov et al., Nat Methods, 2017), or permits to perform neuronal imaging in L2/3 of mouse cortex through intact skull (Wang et al., Nat Methods 2018). Exploiting this new technology, we plan to increase our capability to study the brain structure and functions in different animal models and also to study aspects of pathological conditions otherwise hardly examined due to technological limitations.