aguirreg

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)
   • Lent, R., Azevedo, F. A. C., Andrade-Moraes, C. H. and Pinto, A. V. O. (2011), How many neurons do you have? Some dogmas of quantitative neuroscience under revision. European Journal of Neuroscience. doi: 10.1111/j.1460-9568.2011.07923.x
   • Suzana Herculano-Houzel. (2009) The human brain in numbers: a linearly scaled-up primate brain.
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.