A Visual Pathway for Looming-Evoked Escape in Larval Zebrafish

• Published in: Current biology Vol. 25; no. 14; pp. 1823 - 1834
• Main Authors: Temizer, Incinur, Donovan, Joseph C., Baier, Herwig, Semmelhack, Julia L.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 20.07.2015
• Subjects: Animals; Brain - physiology; Danio rerio; Escape Reaction; Freshwater; Neuropil - physiology; Photic Stimulation; Visual Pathways - physiology; Visual Perception; Zebrafish - physiology
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2015.06.002

Avoiding the strike of an approaching predator requires rapid visual detection of a looming object, followed by a directed escape maneuver. While looming-sensitive neurons have been discovered in various animal species, the relative importance of stimulus features that are extracted by the visual system is still unclear. Furthermore, the neural mechanisms that compute object approach are largely unknown. We found that a virtual looming stimulus, i.e., a dark expanding disk on a bright background, reliably evoked rapid escape movements. Related stimuli, such as dimming, receding, or bright looming objects, were substantially less effective, and angular size was a critical determinant of escape initiation. Two-photon calcium imaging in retinal ganglion cell (RGC) axons revealed three retinorecipient areas that responded robustly to looming stimuli. One of these areas, the optic tectum, is innervated by a subset of RGC axons that respond selectively to looming stimuli. Laser-induced lesions of the tectal neuropil impaired the behavior. Our findings demonstrate a visually mediated escape behavior in zebrafish larvae exposed to objects approaching on a collision course. This response is sensitive to spatiotemporal parameters of the looming stimulus. Our data indicate that a subset of RGC axons within the tectum responds selectively to features of looming stimuli and that this input is necessary for visually evoked escape. •A looming disk elicits escape swims in larval zebrafish•Angular size and expansion rate are key parameters of the looming stimulus•Retinal ganglion cell axons innervating multiple brain areas respond to looming•Lesions of the optic tectum neuropil impair looming-triggered escape responses Visual stimuli that mimic approaching objects induce escape responses in a variety of species. Temizer et al. show that this behavior can be evoked in larval zebrafish and use functional imaging to identify visual areas that respond to approaching objects. They demonstrate that the optic tectum plays a key role in the behavior.