(A) A neural circuit motif in the zebrafish brain that controls the choice to escape left or right, as described by Koyama et al. Auditory signals from cranial nerve VIII (grey) excite the giant Mauthner neurons (blue), which transmit this information down the opposite side of the spinal cord via their axons in order to drive a rapid turn away from the stimulus. Cranial nerve VIII also excites feedforward inhibitory neurons (red), which connect with the Mauthner neurons on both sides, but connect more strongly to the Mauthner neuron on the opposite side of the brain. The feedforward inhibitory populations on each side of the brain also inhibit each other. (B) Left: In response to a non-localized auditory stimulus, fish turn to the left or right with equal probability. Right: destroying the feedforward inhibitory neurons on the left disinhibits the feedforward neurons on the right side of the brain. This leads to stronger inhibition of the Mauthner neuron on the left. The fish is therefore more likely to turn to the left, thanks to the firing of the right Mauthner neuron.