Turtle dorsal cortex (dCx), a three-layered corticalarea of the reptilian telencephalon, receives inputsfrom the retina via the thalamic lateral geniculate nu-cleus and constitutes the first cortical stage of visualprocessing. The receptive fields of dCx neuronsusually occupy the entire contralateral visual field.Electrophysiological recordings in awake and anes-thetized animals reveal that dCx is sensitive to thespatial structure of natural images, that dCx recep-tive fields are not entirely uniform across space,and that adaptation to repeated stimulation is posi-tion specific. Hence, spatial information can be fou ndboth at the single-neuron and population scales.Anatomical data are consistent with the absence ofa clear retinotopic map ping of thalamocortical pro-jections. The mapping and representation of visualspace in this three-layered cortex thus differ fromthose found in mammalian primary visual cortex.Our results support the notion that dCx performs aglobal, rather than local, analysis of the visual scene.
Spatial Information in a Non-retinotopic Visual Cortex
Reptilian cortex shows excellent visual processing despite poor retinal mapping.
Max Planck Institute for Brain Research
