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Number of neurons in a voxel

In describing fMRI, I often try and communicate the degree of information averaging that is taking place in a single voxel. Here is a computation relevant to this:

  1. Number of neurons in the human cerebral cortex: 16 billion (60 billion glia)
  2. Number of 1mm gray-matter, cortical voxels in an anatomical scan: ~684,000
  3. Number of 1mm gray-matter voxels in a 3mm isotropic functional voxel: 27

Number of neurons in a functional voxel:

{{1.6x10^10}/684000}*27 ≈ 630,000

So, there are roughly 630 thousand neurons in a given functional (cerebral cortical) voxel, and roughly 4 times as many glial cells.

An earlier version of this page had an estimate that was an order of magnitude larger, and derived from a widely cited (but apparently erroneous) rule-of-thumb of the number of cortical neurons.

public/neurons_in_a_voxel.txt · Last modified: 2012/09/12 19:09 by aguirreg