title: Early specification of the hierarchical organization of visual cortical areas in the macaque monkey.
abstract: The laminar organization of cortico-cortical projection neurons (expressed by the percentage of supragranular projecting neurons - SLN%) characterizes cortical pathways as feedforward (FF) or feedback (FB) and determines the hierarchical ranking of cortical areas. There is evidence of a developmental reduction in SLN% of pathways to area V1. Here, by analyzing pre- and postnatal projections to area V4, we have been able to address whether developmental reductions of SLN% impact on information processing in the immature cortex. FB pathways to area V4 exhibit 28-84% reduction of SLN%. This contrasts with the FF projections, which show little or no SLN% reduction. However, SLN% values in the immature cortex allocated cortical areas to the same hierarchical levels as in the adult. The developmental reduction of SLN% is a widespread phenomenon in the neocortex and is a distinctive feature of FB pathways. Two mechanisms contribute to developmental changes in SLN%: (i) delayed ingrowth of axons into the cortical target from infragranular layer neurons and (ii) prolonged developmental reduction of the divergence of projections from supragranular layer neurons. The present results show that FF and FB projections exhibit different developmental processes and patterns of connections linking cortical areas and their hierarchical relations are established prenatally, independently of regressive phenomena.
authors.affiliation: Cerveau et Vision INSERM 371, 18 Avenue du Doyen Lépine, 69675 Bron Cedex, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Batardière
authors.forename: Pascal
authors.initials: P
authors.lastname: Barone
authors.forename: Kenneth
authors.initials: K
authors.lastname: Knoblauch
authors.forename: Pascale
authors.initials: P
authors.lastname: Giroud
authors.forename: Michel
authors.initials: M
authors.lastname: Berland
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Dumas
authors.forename: Henry
authors.initials: H
authors.lastname: Kennedy
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000033:anatomy & histology; D005260:Female; D008252:Macaca fascicularis; D009434:Neural Pathways / Q000033:anatomy & histology / Q000196:embryology / Q000254:growth & development; D009474:Neurons / Q000502:physiology*; D011247:Pregnancy; D014793:Visual Cortex / Q000033:anatomy & histology / Q000196:embryology* / Q000254:growth & development*