Mori, Y., Ikezoe, K., Furutaka, K., Kitamura, K., Tamura, H., Fujita, I.
Mapping receptive fields on mouse primary visual cortex: Reverse correlation using two-photon calcium imaging.
Visual information is first received by retinal photoreceptors and then transmitted to the primary visual cortex (V1) where the layout of the visual scene is preserved in a 2D topographic map (retinotopic map). Previous researches have tried to reveal this map by using various methods like sparse sampling from microelectrode recordings and intrinsic optical imaging at low spatial resolution. To obtain a detailed retinotopic map at single-neuron spatial resolution, however, we need to determine both the position of the receptive fields (RFs) for a large number of neurons and the locations of the cell bodies in the cortex simultaneously. Here, we investigated this retinotopic organization in mouse V1 by applying two-photon calcium imaging techniques. Anesthetized mice were presented sequence of dense noise stimuli for more than 3 hours. To obtain the calcium signals at high temporal resolution (scan rate > 30 Hz), we performed arbitrary line scanning where the scan trajectory passed across most of the neuron's cell bodies in the recorded areas. Firing rate changes were reconstructed by temporally deconvolving the signals with sharply rising and exponentially decaying kernel shaped calcium transients. We determined the structure of the RFs for recorded neurons over the cortex by reverse correlating their estimated firing rates with the visual stimuli. RFs were found to exhibit either Gabor-shaped or center-surround structures. Our method also enabled us to reveal the precise position of neurons on the cortex. The RFs of nearby neurons highly overlapped with each other, while their center positions smoothly changed along the tangential direction of the cortex. By contrast, preferred stimulus orientation differed between neighboring neurons. The present results at single-neuron resolution support the notion the that map of visual space in mouse V1 has uniform coverage of stimulus position and orientation.