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Cerebral Cortex Advance Access originally published online on February 2, 2009
Cerebral Cortex 2009 19(10):2380-2395; doi:10.1093/cercor/bhn259
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Thalamic Input to Distal Apical Dendrites in Neocortical Layer 1 Is Massive and Highly Convergent

Pablo Rubio-Garrido1,2, Flor Pérez-de-Manzo1, César Porrero1, Maria J. Galazo1 and Francisco Clascá1

1 Department of Anatomy and Neuroscience, School of Medicine, Autónoma University, Madrid E28029, Spain, 2 Department of Basic Medical Science, School of Medicine, San Pablo-CEU University, Madrid E28660, Spain

Address correspondence to Dr Francisco Clascá, Department Anatomía y Neurociencia, Facultad de Medicina, Universidad Autónoma, Avenue Arzobispo Morcillo s/n., Madrid E-28029, Spain. Email: francisco.clasca{at}uam.es.

Input to apical dendritic tufts is now deemed crucial for associative learning, attention, and similar "feedback" interactions in the cerebral cortex. Excitatory input to apical tufts in neocortical layer 1 has been traditionally assumed to be predominantly cortical, as thalamic pathways directed to this layer were regarded relatively scant and diffuse. However, the sensitive tracing methods used in the present study show that, throughout the rat neocortex, large numbers (mean ~4500/mm2) of thalamocortical neurons converge in layer 1 and that this convergence gives rise to a very high local density of thalamic terminals. Moreover, we show that the layer 1–projecting neurons are present in large numbers in most, but not all, motor, association, limbic, and sensory nuclei of the rodent thalamus. Some layer 1–projecting axons branch to innervate large swaths of the cerebral hemisphere, whereas others arborize within only a single cortical area. Present data imply that realistic modeling of cortical circuitry should factor in a dense axonal canopy carrying highly convergent thalamocortical input to pyramidal cell apical tufts. In addition, they are consistent with the notion that layer 1-projecting axons may be a robust anatomical substrate for extensive "feedback" interactions between cortical areas via the thalamus.

Key Words: cerebral cortex • cortical microcircuit • dendrites • pyramidal neuron • thalamus • top–down interactions


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[Abstract] [Full Text] [PDF]


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