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Neuroscientists: What is a Principal Cell Layer?

  1. Feb 6, 2012 #1
    Hello neuroscientists,

    I'm currently working on a neuroscience project and in the course of the papers I'm reading, I keep coming up against the phrase "principal cell layer". The papers I'm reading are about the hippocampus. I gather that this has something to do with the presence of somas, but what exactly does it mean? What distinguishes these from other layers?

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  3. Feb 6, 2012 #2


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  4. Feb 6, 2012 #3
    Thanks, so, to be absolutely clear, principal cell is just a synonym for projection neuron? And a principal cell layer is just a layer that contains mainly projection neurons, rather than interneurons?
  5. Feb 7, 2012 #4


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    Here's my understanding from looking at the above references and http://neuralnetoff.umn.edu/mediawiki/index.php/Hippocampal_Anatomy.

    Yes, a principal cell is in general a synonym for a projection neuron. The principal cells in the dentate gyrus are granule cells, and these project to CA3. The principal cells in CA3 are pyramidal neurons and these project to CA1. The principal cells in CA1 are pyramidal neurons and these project to the subiculum.

    Although each of the principal cell layers may have more principal neurons than interneurons, I don't think that's part of the definition of a principal cell layer. A principal cell layer is defined by containing the cell bodies of principal neurons. These layers seem pretty well defined anatomically if you look at the pictures in http://neuralnetoff.umn.edu/mediawiki/index.php/Hippocampal_Anatomy.
    Last edited: Feb 7, 2012
  6. Feb 7, 2012 #5


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    Yes. Principal or projection neurons are the cells whose axons travel to the next brain area in the functional pathway, while the interneurons remain local. When talking about projection layers, it's referring to a layer of projection cells grouped with axons all heading to the same place. This organization is very evident in the cortex, for example, where there are also clear differences in cell morphology from layer to layer, and each layer mainly projects to a location distinct from the layer above or below it.
  7. Feb 9, 2012 #6
    Thanks for clarifying everybody, I think the question has been put to rest.
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