Fortunately, neurons are still orders of magnitude above atoms in terms of volumetric density. So it is not that bad. Simulating all of the atoms in the volume of a brain individually might be a pain.
@zanny: A lot of the action in the brain seems to take place at the synapses. These are much smaller structures, and a useful brain scan will need to make precise measurements of the strength of each synapse. I need to study this more closely, but at the moment, I think these measurements maybe impeded by the uncertainty principle.
