What prevents zebrafish from biting off more than it can chew?

WASHINGTON - Scientists may have found why it is easier for us to spot movement of small objects in our field of vision, than to notice other things.

University of California researchers followed entire populations of retinal and brain cells in their test animal: the zebrafish larva, and solved some of the mysteries of its neural circuit that underlies its vision.

The brain region of the zebrafish that receives input from the retina, called the optic tectum, is separated into layers. The top layer receives direct connections from retinal cells, and has a population of both excitatory and inhibitory neurons. These neurons connect to output neurons that project to other brain regions that control how the zebrafish chases prey.

The team found that a large visual stimulus covering the entire field of vision results in low output neuron activity but small items moving across the zebrafish’s field of vision at a prey-like speed activate the output neurons very well.

This happens because large visual stimuli massively activate the inhibitory cell population and inhibit the output cells, while small moving objects activate only a small number the inhibitory tectal cells, enabling the excitation to drive the output cells efficiently.

This mechanism gives the zebrafish good hunting responses to appropriate visual cues, and thereby helps keep it from biting off more than it can chew.

The research team’s findings were published in the October 29 issue of Science. (ANI)