A genuine layer 4 in motor cortex with prototypical synaptic circuit connectivity

Naoki Yamawaki, Katharine Borges, Benjamin A. Suter, Kenneth D. Harris, Gordon M.G. Shepherd

Research output: Contribution to journalArticlepeer-review

46 Scopus citations

Abstract

The motor cortex (M1) is classically considered an agranular area, lacking a distinct layer 4 (L4). Here, we tested the idea that M1, despite lacking a cytoarchitecturally visible L4, nevertheless possesses its equivalent in the form of excitatory neurons with input-output circuits like those of the L4 neurons in sensory areas. Consistent with this idea, we found that neurons located in a thin laminar zone at the L3/5A border in the forelimb area of mouse M1 have multiple L4-like synaptic connections: excitatory input from thalamus, largely unidirectional excitatory outputs to L2/3 pyramidal neurons, and relatively weak long-range corticocortical inputs and outputs. M1-L4 neurons were electrophysiologically diverse but morphologically uniform, with pyramidal-type dendritic arbors and locally ramifying axons, including branches extending into L2/3. Our findings therefore identify pyramidal neurons in M1 with the expected prototypical circuit properties of excitatory L4 neurons, and question the traditional assumption that motor cortex lacks this layer.

Original languageEnglish (US)
Article numbere05422
Pages (from-to)e05422
JournaleLife
Volume3
DOIs
StatePublished - 2014

Keywords

  • layer 4
  • microcircuit
  • mouse
  • neocortex
  • neuroscience
  • pyramidal neuron
  • thalamocortical

ASJC Scopus subject areas

  • Neuroscience(all)
  • Immunology and Microbiology(all)
  • Biochemistry, Genetics and Molecular Biology(all)

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