Active filtering of sequences of neural activity by recurrent circuits of sensory cortex.

In daily life, organisms interact with a sensory world that dynamically changes from moment to moment. Recurrent neural networks can generate dynamics, but in sensory cortex any dynamic role for the dense recurrent excitatory-excitatory network has been unclear. Here we show a new role for recurrent connections in mouse visual cortex: they support powerful dynamical computations, but via filtering sequences of input instead of generating sequences. Using two-photon optogenetics, we measure responses to natural images and play them back, showing amplification when played back during the correct movie dynamic context and suppression in the incorrect context. The sequence selectivity depends on a network mechanism: inputs to groups of cells produce responses in different local neurons, which interact with later inputs to change responses. We confirm this mechanism by designing sequences of inputs that are amplified or suppressed by the network. Together, these data suggest a novel function, sequence filtering, for recurrent connections in cerebral cortex.