Experimental Brain Research

, Volume 80, Issue 1, pp 49–53 | Cite as

Conserved patterns of cortico-cortical connections define areal hierarchy in rat visual cortex

  • T. A. Coogan
  • A. Burkhalter


The prevalence of reciprocal connections in the cerebral cortex indicates that they play a fundamental role in the processing of sensory information. We have investigated the laminar termination patterns of such paired connections between different visual cortical areas of the rat, and have found two basic projection types: one which includes layer 4 and a second which includes layer 1 and avoids layer 4. The projections from primary visual cortex (area 17) to extrastriate visual cortical targets in the cytoarchitectonical areas 18a and 18b, and from 18a to a site in 18b, are of the first type. In contrast, the return projections from 18a and 18b to area 17 and from 18b to 18a, are of the second type. Thus each pair of connections has one element of each type, giving every circuit a nearly identical asymmetric structure. These laminar patterns resemble those of forward and feedback connections in primate cortex, indicating that cortico-cortical connectivity patterns are highly conserved through evolution, and that, as in monkeys, these connections define a hierarchical organization of areas in rat visual cortex.

Key words

Hierarchical processing Sensory cortex Reciprocal connections Rat 


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Copyright information

© Springer-Verlag 1990

Authors and Affiliations

  • T. A. Coogan
    • 1
  • A. Burkhalter
    • 1
  1. 1.Department of Neurology and Neurological Surgery (Neurosurgery), and McDonnell Center for Studies of Higher Brain FunctionWashington University School of MedicineSt. LouisUSA

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