Spatial Information in a Non-retinotopic Visual Cortex

Turtle dorsal cortex (dCx), a three-layered cortical area of the reptilian telencephalon, receives inputs from the retina via the thalamic lateral geniculate nucleus and constitutes the first cortical stage of visual processing. The receptive fields of dCx neurons usually occupy the entire contralateral visual field. Electrophysiological recordings in awake and anesthetized animals reveal that dCx is sensitive to the spatial structure of natural images, that dCx receptive fields are not entirely uniform across space, and that adaptation to repeated stimulation is position specific. Hence, spatial information can be found both at the single-neuron and population scales. Anatomical data are consistent with the absence of a clear retinotopic mapping of thalamocortical projections. The mapping and representation of visual space in this three-layered cortex thus differ from those found in mammalian primary visual cortex. Our results support the notion that dCx performs a global, rather than local, analysis of the visual scene.