The BBC says
47 people got 18FDG Positron Emission Tomography. This method measures brain glucose use as a proxy for how hard cells are working. They say that this makes it better than other kinds of PET which merely measure regional blood flow. I bet they really wanted to do this study with fMRI, because PET scans cost loads, but of course you can't take a cellphone into an MRI scanner.
There were two conditions: a control in which they had a phone stuck to each ear but they were both off, and an active condition in which the right-ear phone was switched on and receiving a call - but muted so they couldn't hear anything. Each subject was scanned twice, once under each condition, so that's 94 scans.
What happened? In the Results section they say that (my emphasis):
SPM comparisons on the absolute metabolic measures showed significant increases (35.7 vs 33.3 µmol/100 g per minute for the on vs off conditions, respectively; mean difference, 2.4 [95% CI, 0.67-4.2]; P=.004) in a region that included the right orbitofrontal cortex and the lower part of the right superior temporal gyrus. No areas showed decreases.
In other words a highly signficiant finding of increased glucose uptake in the areas of the brain closest to the cell phone. Whoa, that's big. However, it seems that this result was not corrected for multiple comparisons, because in the table of results they give the corrected p value for the activated cluster as p=0.05 - bang on exactly low enough to be considered significant, but no lower.
Their method for correcting for multiple comparisons was also quite unusual and I'm not quite sure what to make of it. It's on the right-hand column of Page 810. Maybe commentators will be able to offer some insight.
There's a few other things to note here. They show a nice big colorful This Is Your Brain On Phone image but it's a "representative" image of one brain, rather than an averaged image from all subjects. This is really not good practice. It's acceptable - but only because there's no alternative - for data which can't be averaged, like microscope pics.
With between-group comparisons of neuroimaging data, the averages are computed as part of the statistical analysis, and should be shown. With single-subject data we're left having to trust the authors to have really picked a "representative" image as opposed to "the best image".
Second, this has nothing to do with cancer. Brain activation happens all the time and very rarely does it have cancerous consequences. In fact this is so unrelated to cancer that I shouldn't even be mentioning cancer in this post. However, I feel the need to because the BBC (and most other outlets) did. Thus we saw curious paragraphs like this (direct quote):
Since the boom in mobile phone use, there has been considerable interest in the effect on the body. The largest study on 420,000 mobile phone users in Denmark, has not shown a link between phone use and cancer. This small study on 47 people...
Why mention cancer, if the only thing you say about it is that there's no link? Presumably because of the following chain of associations: cell phones use radiation...radiation causes cancer...cell phones and cancer!
I have no idea if cell phones cause cancer. Just from basic biology though, if they were going to cause any cancer, it'd probably be skin cancer rather than brain cancer, since a) they're closest to the skin, not the brain and b) brain cancer is incredibly rare because the brain contains no rapidly dividing cells, whereas skin cancer is common because skin is made of exactly that.
So even if if this increased brain glucose metabolism somehow was related to cancer of the brain, this would be the least of our worries, because if cell phones somehow caused brain cancer, they'd almost certainly cause many times more cases of skin cancer and the brain cancer would be a footnote.
But the point is, this study has nothing to do with cancer so forget I said that. If you have trouble forgetting, just hold your mobile phone over your temporal lobes until your hippocampus is overloaded and you suffer memory loss.
Volkow, N., Tomasi, D., Wang, G., Vaska, P., Fowler, J., Telang, F., Alexoff, D., Logan, J., & Wong, C. (2011). Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism JAMA: The Journal of the American Medical Association, 305 (8), 808-813 DOI: 10.1001/jama.2011.186