  Brain state regulates sensory processing and motor control for adaptive
behavior. Internal mechanisms of brain state control are well studied, but the
role of external modulation from the environment is not well understood. Here,
we examined the role of closed-loop environmental (CLE) feedback, in comparison
to open-loop sensory input, on brain state and behavior in diverse vertebrate
systems. In fictively swimming zebrafish, CLE feedback for optomotor stability
controlled brain state by reducing coherent neuronal activity. The role of CLE
feedback in brain state was also shown in a model of rodent active whisking,
where brief interruptions in this feedback enhanced signal-to-noise ratio for
detecting touch. Finally, in monkey visual fixation, artificial CLE feedback
suppressed stimulus-specific neuronal activity and improved behavioral
performance. Our findings show that the environment mediates continuous
closed-loop feedback that controls neuronal gain, regulating brain state, and
that brain function is an emergent property of brain-environment interactions.
