Primate neocortex performs balanced sensory amplification

Sensory cortex amplifies relevant features of external stimuli. This sensitivity and selectivity arise through the transformation of inputs by cortical circuitry. We characterize the circuit mechanisms and dynamics of cortical amplification by making large-scale simultaneous measurements of single cells in awake primates and by testing computational models. By comparing network activity in both driven and spontaneous states with models, we identify the circuit as operating in a regime of balanced amplification. Incoming inputs are strongly but transiently amplified by recurrent excitation. Inhibition acts to counterbalance this excitation by rapidly quenching responses, thereby permitting tracking of time-varying stimuli. One-Sentence Summary Sensory cortex uses balanced excitatory and inhibitory circuitry to boost weak signals while maintaining fast sensory dynamics in a changing environment.