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Zusammenfassung:
In vivo 2-photon imaging of calcium sensors in visual cortex has provided a host of new insights into the fine scale columnar mapping of response properties like orientation, direction, and visual space. Extracellular recording in carnivores have shown a columnar segregation of ON- and OFF-center geniculate inputs in layer 4, which could provide the basis for the generation of orientation selectivity. However, the spatial arrangement of ON and OFF in layer 2/3 has not been addressed. In this study we used 2-photon imaging of GCamP6s calcium fluorescent signals to map the receptive fields of thousands of neurons in layer 2/3 of tree shrew visual cortex with reverse correlation using sparse noise. We found a diverse array of receptive field properties in layer 2/3 including neurons with classic simple, complex and single sign receptive fields (either ON or OFF). The ON and OFF subfields in layer 2/3 were found to exhibit topologically distinct relationships with the maps of visual space and orientation preference. In most cases, the centers of OFF subfields for neurons in a given region of cortex were confined to a compact region of visual space and displayed a smooth retinotopic progression, while the centers of the ON subfields were distributed over a wider region of visual space and displayed less retinotopic precision. Consistent with the arrangement of ON and OFF subfields of simple cells in other species, the angle of displacement in visual space of the ON and OFF subfields for individual neurons could be used to predict the organization of the orientation map. Taken together, these results suggest that the differential arrangement of ON and OFF subfield centers by cortical circuits meets the conjoint constraints of mapping both visuotopy and orientation in a single population of neurons and in a fashion that preserves continuity for both stimulus features. Meeting abstract presented at VSS 2015.
