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Geniculocortical Input Drives Genetic Distinctions Between Primary and Higher-Order Visual Areas

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Science  07 Jun 2013:
Vol. 340, Issue 6137, pp. 1239-1242
DOI: 10.1126/science.1232806

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Dividing the Brain

The cerebral cortex of the brain is organized into primary cortical areas, which receive direct inputs from the thalamus, and higher-order cortical areas, which in turn receive inputs from one or more primary cortical areas. Chou et al. (p. 1239) investigated the mechanisms underlying the specification of higher-order cortical areas. Input from the dorsal lateral geniculate nucleus into the primary visual area (V1) is required to drive the genetic and functional differentiation of a large visual cortical field into primary and higher-order visual areas. Thalamocortical axon input acts on a large visual cortical field. The afferents from the dorsal lateral geniculate are necessary to further refine the cortex into subareas that distinguish V1 from higher processing areas. In the relatively simple model that emerges from these findings, sensory input is essential to distinguish primary and higher-order cortical areas.

Abstract

Studies of area patterning of the neocortex have focused on primary areas, concluding that the primary visual area, V1, is specified by transcription factors (TFs) expressed by progenitors. Mechanisms that determine higher-order visual areas (VHO) and distinguish them from V1 are unknown. We demonstrated a requirement for thalamocortical axon (TCA) input by genetically deleting geniculocortical TCAs and showed that they drive differentiation of patterned gene expression that distinguishes V1 and VHO. Our findings suggest a multistage process for area patterning: TFs expressed by progenitors specify an occipital visual cortical field that differentiates into V1 and VHO; this latter phase requires geniculocortical TCA input to the nascent V1 that determines genetic distinctions between V1 and VHO for all layers and ultimately determines their area-specific functional properties.

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