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I'm taking an introductory neuroscience course online, and it mentions that of the 55 morphological types and the 11 electrical types, there are 207 morpho-electrical types. How does this work? 55 times 11 is 605, so it's not a simple mapping of 1 to 1. 207 isn't a factor of and doesn't share any proper divisors with 605, but it's roughly 1/3 (but not exactly). I don't see how a third makes sense though.

What causes exactly 207 morpho-electrical types?

Feel free to let me know if I should move this to Health or Psychology.SE, I'm not quite sure where to post this.

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  • $\begingroup$ Was there a citation for this number? I definitely don't think this is a settled conclusion. $\endgroup$ – Seanny123 Jan 4 '18 at 4:00
  • $\begingroup$ @Seanny123 No, but this paper was co-published by the same author and seems to mention that number. $\endgroup$ – Riker Jan 4 '18 at 15:23
  • $\begingroup$ I would add those references to your question since they seem quite relevant. $\endgroup$ – Seanny123 Jan 5 '18 at 0:04
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This is just that one author's opinion - it is telling that both sources you have for the number come from the same author. Henry Markram has a leadership role in the Blue Brain Project, a project to create a very detailed computer simulation of a chunk of neocortex to answer various questions. In the context of this project, it is somewhat necessary to make some decisions about numbers of cell types so that they can be incorporated in the model. People can bicker all day long about which types are actually unique types, though.

As far as the mathematics of having 55 morphological types and 11 electrical types, yet only 207 morpho-electrical types rather than 605, the answer is that the matrix is sparse. To get 605 types, you would need to observe all 11 electrical types within each of the 55 morphological categories. If not every electrical type is observed for a given morphological type, you will have less than 605 total. In some cases morphological types are specifically associated with particular electrical types.

You should also read about the concept of lumpers and splitters - in summary, in any context of classification without clear distinctions, different people will come up with different boundaries. It isn't really possible to argue "right" versus "wrong" in this context, because doing so requires weighting different values. Lumping may be beneficial for the sake of simplicity and generalization but miss some details; splitting may allow for more nuance but also risks not seeing "the forest for the trees."

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