Topographical Organization Of Neural Maps In The Visual Information Processing

The mammalian visual systems evolved to accurately represent the scene in the world. Knowing the visual attribute organization within visual cortices is crucial for us to understand visual information processing. A fundamentally organized principle of the visual system is the use of space to code information. This topographical mapping is characterized as nearby neurons share similar responsive profiles, thereby preserving spatial order, among visual systems from rodents to non-human primates. A prevailing example is the retinotopic map in the visual system. However, for other visual feature representations, are there common principles used in the formation of all neural maps remains unclear. In the present study, we used intrinsic optical imaging and electrophysio logical recording techniques to explore the functional organization of visual attributes at both population and single-cell levels among different species. The study included three experiments:Firstly, we investigated the topographic organization of the cutoff spatial frequency (SF) map in mouse V1. Mice are not known for their excellent vision. However, a growing number of scientists have begun using mice to explore the mechanisms underlying visual processing due to the genetic tools available to label and manipulate specific cell types and circuits. Although the effort is far from complete, these studies generally support the argument that the mouse visual system is much more sophisticated than previously thought. In this study, we revealed an increasing gradient in the population responses of mice V1to stimulus SF from the anterior to the posterior part, which represents the lower and the upper visual field respectively. This organization was present at eye opening and persisted through adulthood. Dark rearing delayed the refinement of visual acuity globally, but had little impact on the topographical organization of the cutoff SF, suggesting that the regional distribution of spatial resolution is innately determined.Secondly, we studied the topographical organization of preferred SF map in cat area17. Maps of SF in cat V1have been described in detail by brain imagings. Recent imaging experiments further suggest that the SF organization in V1displays a global anteroposterior SF gradient. In this study, using intrinsic signal optical imaging, we also found an anteroposterior distribution of SF preference within a limited imaging area. However, we next showed unequivocally that neurons with the highest SF selectivity concentrated around the horizontal meridian when we extended the region of interest to lambda suture, exposing the most posterior part of V1, where corresponding to-10degree of visual fields upper of the horizon. The electrophysiological recordings further demonstrated neurons with receptive field around horizontal meridian had the highest spatial preferences. Our results provide essential information for the comprehensive understanding of the SF organization in cat V1.Lastly, we focused on functional organization for color-evoked domains in macaque visual cortices. The non-human primate visual system is one of the mostpopular model system for studying visual mechanisms for information processing due to its more refined visual system, including larger cortical area, higher visual acuity, visual feature columns and hue sensitivity. In this study, we try to study the functional organization for color-evoked domains in macaque V1,V2and V4respectively. We found that domains that respondedto color and orientation stimuli were largely separate from preferring domains in these visual cortices, especially in V2and V4. The excellent results in V2illustrated a topographical hue preferring structure as they are distributed in CIE1931color space. We then compared the size and number of color evoked domains between V1, V2and V4, the bigger and bigger of these modules revealed there is an increasing concentration of color processing along V1, V2and V4.By these three experiments, we studied the organization of visual feature maps in visual cortices among different species.Our results indicate the topographical organization of neural maps is ubiquitous in visual system. Representations of this organization clearly depend on the development of highly organized neuronal projections from the periphery to the brain. As a result, the cortex would process visual information more efficient due to the coordinated changes in synaptic strength and neuronal morphology.