Giant neuron is a key player for fast escape

Abstract

Escape behaviors are crucial to survive predator encounters or aversive stimuli. The neural circuits mediating escape reactions of different animals have a common framework to trigger extremely fast and robust movement with minimum delay. Thus, the escape networks possibly represent functional architectures to perform most efficient sensory-motor processing in the brain. Here we review escape behaviors and underlying circuits of squid, crayfish, fruit fly, zebrafish and rodent. The escape circuits of these animals involve giant neurons, or also called as giant fibers or giant axons, to initiate fast escape. Without activation of the giant neurons, the animals can do escape or similar behaviors typically in response to less precious threads, but they are delayed and much slower than fast escape initiated by the giant neurons. Therefore, fast and slow escape circuits are built, probably in parallel, in the brain and the giant neurons play a key role to induce fast escape to avoid imminent danger. We also discuss why the giant neurons are built in the fast escape circuits by introducing their advantage to collect sensory information and to send ballistic motor output as fast as possible.