Visualizing mammalian brain area interactions by dual-axis two-photon calcium imaging

Fluorescence Ca2+ imaging enables large-scale recordings of neural activity, but collective dynamics across mammalian brain regions are generally inaccessible within single fields of view. Here we introduce a two-photon microscope possessing two articulated arms that can simultaneously image two brain areas (similar to 0.38 mm(2) each), either nearby or distal, using microendoscopes. Concurrent Ca2+ imaging of similar to 100-300 neurons in primary visual cortex (V1) and lateromedial (LM) visual area in behaving mice revealed that the variability in LM neurons' visual responses was strongly dependent on that in V1, suggesting that fluctuations in sensory responses propagate through extended cortical networks.