Abstract
The motion after-effect (MAE) in human perception has been studied because it gives us good insights for understanding motion processing in the visual system. Visual function of Zebrafish (Danio rerio), which is a simple model vertebrate amenable to genetics, has been studied using optokinetic response or optomotor response. In this study, we demonstrate the existence of MAE in the optomotor response of zebrafish. Vertical square-wave drifting gratings were presented to freely swimming adult zebrafish as adaptation stimuli. A circular transparent fish tank (9.5 cm in diameter) was surrounded by computer monitors for stimulus presentation. A non-transparent column (4 cm in diameter) was also placed in the center of the fish tank for monocular stimulus presentation. During presentation of drifting gratings at a constant velocity (300 deg/s), zebrafish intermittently pursued the drifting gratings. We changed spatial frequency of gratings and identified the frequency band which stably elicited this optomotor response (OMR) in zebrafish. Then, applying the most appropriate spatial frequency for eliciting OMR as the stimulus parameter, we investigated behaviors of zebrafish after presentation of drifting gratings. Just after cessation of stimulus movement (stimulus was changed into uniform gray background), zebrafish showed turning response as if the stimulus were moving in the opposite direction. This phenomenon indicates that adaptation of motion stimuli elicited MAE in OMR of zebrafish. In addition, as the duration of adaptation period increased, the behavioral response delay became shorter. Combining physiological studies and this experimental system might contribute to clarify not only neural mechanisms of MAE, but also general computation manner of motion direction in the visual system.
This study is supported by funds to H.I. (Grant-in-Aid for Science Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan #22730586, Senshu University Research Grant #H21).