How does a fish make a split-second escape decision?

What is it about?

Many fish are capable of performing a fast start in response to critical situations – one of the fastest behavioral responses in the vertebrate world. This response consists of a rapid body bend known as the short-latency C-start and is triggered by a pair of large neurons in the brain that act as a decision hub. Interestingly, escape responses triggered by vision are much slower than those triggered by vibrations in the water. In this study, we asked a fundamental question: where does the extra time go when a visual stimulus triggers a fast start? To address this, we traced the flow of visual information from the eye, via the optic nerve and optic tectum, to the Mauthner neurons that initiate the fast start. Our results show that most of the transmission time from the eye to the Mauthner neuron is spent in the eye itself – on phototransduction and retinal processing. In contrast, processing time in the optic tectum is very limited. We also show that the connectivity pattern supports a high degree of flexibility in the directionality of visually induced fast starts. Our findings thus highlight how visual processing supports fast yet flexible decisions.

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Why is it important?

The study provides important mechanistic insights into the sensory-motor transformation underlying the fast-start behavior and offers a foundation for comparative analyses of the evolutionary trajectories of the Mauthner system.