  Fluorescence is a powerful mean to probe information processing in the
mammalian brain. However, neuronal tissues are highly heterogeneous and thus
opaque to light. A wide set of non-invasive or invasive techniques for
scattered light rejection, optical sectioning or localized excitation, have
been developed, but non-invasive optical recording of activity through highly
scattering layer beyond the ballistic regime is to date impossible. Here, we
show that functional signals from fluorescent time-varying sources located
below an highly scattering tissue can be retrieved efficiently, by exploiting
matrix factorization algorithms to demix this information from low contrast
fluorescence speckle patterns.
