title: Collision-sensitive neurons in the optic tectum of the bullfrog, Rana catesbeiana.
abstract: In this study, we examined the neuronal correlates of frog collision avoidance behavior. Single unit recordings in the optic tectum showed that 11 neurons gave selective responses to objects approaching on a direct collision course. The collision-sensitive neurons exhibited extremely tight tuning for collision bound trajectories with mean half-width at half height values of 0.8 and 0.9° (n = 4) for horizontal and vertical deviations, respectively. The response of frog collision-sensitive neurons can be fitted by a function that simply multiplies the size dependence of its response, e(-αθ(t)), by the image's instantaneous angular velocity θ'(t). Using fitting analysis, we showed that the peak firing rate always occurred after the approaching object had reached a constant visual angle of 24.2 ± 2.6° (mean ± SD; n = 8), regardless of the approaching velocity. Moreover, a linear relationship was demonstrated between parameters l/v (l: object's half-size, v: approach velocity) and time-to-collision (time difference between peak neuronal activity and the predicted collision) in the 11 collision-sensitive neurons. In addition, linear regression analysis was used to show that peak firing rate always occurred after the object had reached a constant angular size of 21.1° on the retina. The angular thresholds revealed by both theoretical analyses were comparable and showed a good agreement with that revealed by our previous behavioral experiments. This strongly suggests that the collision-sensitive neurons of the frog comprise a threshold detector, which triggers collision avoidance behavior.
authors.affiliation: Department of Brain Science and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Fukuoka, Japan. naka@brain.kyutech.ac.jp
authors.forename: Hideki
authors.initials: H
authors.lastname: Nakagawa
authors.forename: Kang
authors.initials: K
authors.lastname: Hongjian
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D016014:Linear Models; D008297:Male; D009039:Motion Perception / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D011892:Rana catesbeiana; D013477:Superior Colliculi / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology