[thedoc (OP)]

Radioactivity released by Cold War nuclear tests has enabled Swedish scientists to probe how adult brains produce new nerve cells...

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[CliffordK]

I'm not sure if that study tells one anything.
We already know that nerve cells make new dendritic and axonal connections throughout their lives.  One would expect cell walls and various proteins to be replaced throughout the life cycle of the cells.

The approach, however, is interesting.

A much better study would be to isolate the neurons from the glia cells.
Then isolate the DNA from the neurons.
Then carbon date just the DNA as current theory would indicate that the DNA would be one molecule that would not be replaced during the life of the cells.

[chris]

I disagree, Clifford. The fact that new nerve cells were being born was known; but what was contentious was whether any of those newborn neurones actually survived for any appreciable length of time. Being born is one thing, but if you die a neuronal death a day later, arguably you are going to make very little contribution to brain function. But if you persist for a significant period of time, then other observations such as the link between the birth rate of these cells and conditions like depression, begin to make a lot more sense; moreover, new avenues open up in terms of important research questions.

Also, to address you final point, they did indeed isolate the neurones from the glia and do the carbon-dating experiment on both cell types individually.