Visual motion processing subserving behavior in crabs

•Crabs constantly adjust the speed and direction of escape based on visual information.•Giant neurons convey visual information on the speed and direction of moving objects.•Identified giant neurons hold long-term visual memory traces.•A microcircuit of giant neurons may operate as a decision making node.

Motion vision originated during the Cambrian explosion more than 500 million years ago, likely triggered by the race for earliest detection between preys and predators. To successfully evade a predator's attack a prey must react quickly and reliably, which imposes a common constrain to the implementation of escape responses among different species. Thus, neural circuits subserving fast escape responses are usually straightforward and contain giant neurons. This review summarizes knowledge about a small group of motion-sensitive giant neurons thought to be central in guiding the escape performance of crabs to visual stimuli. The flexibility of the escape behavior contrasts with the stiffness of the optomotor response, indicating a task-dependent early segregation of visual pathways.