UC San Diego

The mouse visual cortex is a hierarchical and distributed system that consists of primary visual cortex and several higher visual cortical areas. Historically, the low acuity of the mouse visual system garnered little interest in the neuroscience community, so many key principles about visual and cortical circuits were first discovered in primate and cat vision. As transgenic mice and genetically targeted viral tools and novel recording methods developed, a renewed interest and appreciation in the mouse visual system has emerged. A detailed understanding of the mouse visual system on its own, as well as in comparison with other species, is critical for understanding how different visual areas and their cell types work to process visual input. In chapter one, two methods for recording single cell activity are used to measure the spatiotemporal frequency and direction tuning properties of deep layer cortical neurons in primary visual cortex and two higher visual areas. While previous studies have characterized the functional tuning properties of superficial (layer 2 and layer 3) neurons in mice, the tuning properties of deep layer (layer 5 and 6) and different projection classes of layer 5 neurons have been less well characterized. We use extracellular electrophysiology and two-photon calcium imaging and find that while deeper layer neurons are specialized for different spatial and temporal frequencies, there is also a greater overlap in tuning preferences than previously reported in superficial layers. We also find much stronger direction tuning in extratelencephalically projecting layer 5 neurons compared to intratelencephalically projecting layer 5 neurons in multiple visual areas. In chapter two, we examine if two different transgenic mouse lines label layer 4 neurons that may represent different spatial and temporal frequency channels in mice to determine if the organization of spatial and temporal frequency channels is conserved from primates. We find that the neurons labelled in layer 4 by these two mouse lines are both morphologically and functionally different. Together, this dissertation seeks to use modern neuroscience tools to elucidate a more detailed understanding of the functional organization of visual tuning in the mouse visual system.