Abstract
Purpose: :
To determine the direction of object motion, multiple local motions must be combined and computed in the brain. When superimposed, two moving gratings appear to form a single 'plaid' pattern. The two grating components generate individual responses in local motion detectors. In higher brain areas this information can be put together by pattern-selective cells that respond to the movement of the plaid pattern rather than the individual gratings. Here, we analyze the integration of plaid stimuli in the visual system of zebrafish larva.
Methods: :
We examined zebrafish larva by measuring tectal activity as well as their behavioral response to different visual stimulation patterns. Larva were immobilized; then we presented grating patterns for 1s moving in 45° angles to the upper right (45°-right), upper left corner (45°-left) of the stimulation screen, or an overlay of these stimuli, resulting in a plaid stimulus moving upwards. Tectal activity to these stimuli was recorded by 2-photon microscopy after bolus-injection of OGB-1/AM. We used the same stimuli for the behavioral experiments but presented the stimuli on a horizontally mounted LCD-screen for 25s. The optomotor response (OMR) of the larva to the respective stimuli was assessed in a 20cm petri dish, separated into 3 sectors referring to the 3 apparent stimulus directions (left, mid, right).
Results: :
So far, we identified several direction-sensitive cells in the visual tectum of 5 dpf larva. Stimuli moving in the preferred direction evoked large calcium transients (~30% ΔF/F) measured by selecting regions of interests surrounding the somata. In our OMR-setup we found that the larva performed the behavior in the expected directions. If exposed to the 45°-right stimulation, 55.7% of the larva followed the stripes and accumulated in the right sector of our setup (Other sectors: left 4.9%; mid 11.5%). If stimulated with the 45°-left stimulation, 47.5% of the larva were found in the left sector. The plaid stimulus was detected as a straight movement and thus 29.5% of the larva were found in the mid sector (left: 4.9%; right: 9.8%). Further two-photon recordings will aim on the spatial organization of direction and orientation sensitive cells in the tectum. In addition, we seek to identify pattern-selective cells and their spatial organization.
Conclusions: :
So far, these data are consistent with the hypothesis that zebrafish larva can see moving plaid patterns and follow the movement of the pattern rather than its components.
Keywords: retinal connections, networks, circuitry • vision and action • imaging/image analysis: non-clinical