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There is a mean number of synapses per neuron in the human brain which is not very well known, but is of order 10,000. (Some say, it's about 6,000, other say it's about 50,000.)

What is known about the distribution of the number of synapses - in a very rough sense?

The number is most certainly not distributed normally around one mean value of about 10,000 (because there are very different types of neurons).

More probable, there are some types of neurons with typical mean numbers of synapses (each distributed normally), which would give a distribution like this:

enter image description here

For the sake of simplicity I want to ask:

If we were to group numbers of synapses roughly into bins of powers of ten, how high would be the peaks, roughly?

enter image description here

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  • $\begingroup$ You are correct, depending on the neuronal cell type or location in the brain (cerebellum versus a cortical layer for instance), the number of synapses will differ. I don't know if this has been systematically studied, cell type by cell type, region by region, so that the statistics you are looking for would be available... I imagine that work will be painstaking and difficult (particularly with the human brain) but the connectome project is making huge strides and is the likely source in the future for such information. $\endgroup$ – Louis Leung Nov 4 '17 at 9:18
  • $\begingroup$ @LouisLeung: Do you accidently know a specific resource inside the connectome project which points into this direction? $\endgroup$ – Hans-Peter Stricker Nov 5 '17 at 0:15
  • $\begingroup$ The exquisite serial EM reconstruction of neurons with identifiable (and thus quantifiable) synapses has been demonstrated here: conte.harvard.edu/connectomics. This paper at: ncbi.nlm.nih.gov/pubmed/26232230 has some synaptic statistics though it is volume- and not cell-specific which I believe is what you are after. $\endgroup$ – Louis Leung Nov 5 '17 at 7:05

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