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Elife. 2014 Dec 19;3:e05422. doi: 10.7554/eLife.05422.

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

Author information

1
Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, United States.
2
Institute of Neurology, University College London, London, United Kingdom.

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.

KEYWORDS:

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

PMID:
25525751
PMCID:
PMC4290446
DOI:
10.7554/eLife.05422
[Indexed for MEDLINE]
Free PMC Article

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