Abstract
In the presence of moving visual stimuli, the majority of animals follow the Fourier motion energy (luminance), independently of other stimulus features (edges, contrast, etc.). While the behavioral response to Fourier motion has been studied in the past, how Fourier motion is represented and processed by sensory brain areas remains elusive. Here, we investigated how visual moving stimuli with or without the first Fourier component (square-wave signal or missing fundamental signal) are represented in the main visual regions of the zebrafish brain. First, we monitored the larva's optokinetic response (OKR) induced by square-wave and missing fundamental signals. Then, we used two-photon microscopy and GCaMP6f zebrafish larvae to monitor neuronal circuit dynamics in the optic tectum and the pretectum. We observed that both the optic tectum and the pretectum circuits responded to the square-wave gratings. However, only the pretectum responded specifically to the direction of the missing-fundamental signal. In addition, a group of neurons in the pretectum responded to the direction of the behavioral output (OKR), independently of the type of stimulus presented. Our results suggest that the optic tectum responds to the different features of the stimulus (e.g., contrast, spatial frequency, direction, etc.), but does not respond to the direction of motion if the motion information is not coherent (e.g., the luminance and the edges and contrast in the missing-fundamental signal). On the other hand, the pretectum mainly responds to the motion of the stimulus based on the Fourier energy.
Highlights
Visual motion signals are composed of several features that the visual system needs to extract to detect movement
To investigate how Fourier components of moving visual stimuli are represented in the optic tectum and the pretectum, we presented to transgenic zebrafish larvae expressing panneuronally the genetically encoded calcium indicator GCaMP6f (Huc:H2B-GCaMP6f), vertical square-wave gratings and the corresponding missing-fundamental signal while monitoring neural circuits calcium dynamics by means of two-photon microscopy
Several studies have demonstrated that the missing-fundamental stimulus induces motion perception in the direction of the Fourier energy in humans (Chen et al, 2005; Sheliga et al, 2005) and monkeys (Miura et al, 2006), and correlate with the behavioral output of the optokinetic response (OKR) in mice (Sugita et al, 2012) and the optomotor response (OMR) in zebrafish (Orger et al, 2000)
Summary
Visual motion signals are composed of several features that the visual system needs to extract to detect movement. Studies using modified square-wave moving gratings in which the first-Fourier component was suppressed (missing-fundamental signal), showed that the perception of movement is dominated by the Fourier components of the signal. Using Fourier decomposition, it is possible to create a stimulus that has a Fourier motion energy moving in the opposite direction to that of the other features (edges, Fourier Motion Processing in Zebrafish contrast, textures, etc.) by removing the fundamental frequency of the square-wave. This stimulus is called the missingfundamental stimulus (sometimes depicted as fluted-squarewave) (Adelson and Bergen, 1985; Chen et al, 2005)
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