[alwaysAttending]

An IQ test wouldn't indicate more neurons.

[lqdc13]

They can infer size with fMRI.

The article claims it's good for the brain. What does it mean to be "good for the brain"?

What people want to know is not how many neurons there are but whether cognition gets better. And that is indeed the case:

http://www.ncbi.nlm.nih.gov/pubmed/21282661