The BBC report that ‘using a mobile phone affects the Brain‘. Just before this story appeared I was sent the paper on which the story was based. “Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Mechanism” by Nora D Volkow et al published in the Journal of the American Medical Association (JAMA February 23, 2011-Vol 305, No8 pages 808-813). The paper is not freely available but you can read the abstract here. This is a nicely constructed study which looked for the effects of mobile phone use on brain metabolism and reports that brain activity (as measured by uptake of glucose) increases during exposure to mobile phone radiation. With delightful understatement, the last line of the conclusions section of their abstract says: ”
The result is of unknown clinical significance
However I think this work is flawed, and I think the cause of the flaw shows exactly how hard it is to detect this kind of effect. All the PET imaging aspects seem impeccable to me – I am not expert in this field, and the protocol used – a single blind trial – in which the subjects did not know when (or if) the mobile phone held near their head was activated, seems reasonable. However the estimation of the RF dose seems to me overly simplistic. Let me explain.
- The authors assumed the phone was a dipole radiator – yielding a particularly simple pattern of emitted radiation. The wavelength of the mobile phone radiation at 800 MHz is around 30 cm, and for a distance around the phone of roughly one wavelength, the emission pattern is complex: the so called ‘near field’ pattern. Why is it complex? Because the antennae in the phone are squeezed into odd shapes to make them fit inside the tiny handsets consumers demand. Every handset is different, and I have seen results from a wide variety of phones and the results do not look like dipole radiation patterns. So there is absolutely no reason to assume that emission pattern was like a dipole, however the researchers did not measure the actual emission pattern. This is a critical failure because (a) with the right equipment it’s only a couple of hours work and (b) their assertion that glucose metabolism levels are related to electrical field levels in the brain depends solely on their estimate of emission pattern of the phone. [See Author Reponse below]
- Secondly, they simply switched the phones on and transmitted a voice message on tape to the phones. The phones were muted so the subject did not know whether the phones were on or not. The problem here is that the subjects did not speak. Most mobile phones employ a protocol called Discontinuous Transmission (DTX) which switches off the transmission function of the phones when the phone is not required to transmit (this saves on battery life). The authors don’t discuss this, and perhaps they were not aware of this, but if you don’t speak and the room is modestly quiet, the phone will barely transmit any RF signal. So there is actually no evidence of the dose of RF radiation produced.[See Author Reponse below]
The reason these issues are a problem is that, as the figure at the head of the paper shows, the metabolic activity across the brain changed quite a bit between data taken with the phone on and with the phone off. The average glucose metabolism is unchanged across the whole brain, but the researchers have picked one area of the brain and said that changes in this area of the brain are significant. The problem is that, as I have mentioned, I am not convinced that there is anything special about that area of the brain in terms of exposure to RF radiation. I am sure the authors would reply that “over the 47 subjects studied, if the area wasn’t significant then why would there be any effect when averaging all subjects?” And I would reply, “I don’t know, but’s it’s your job show that there is a relationship between dose and signal, not mine.” And then…
Michael: What’s your problem? Are you ‘on the side of’ mobile phone companies? What’s wrong with work that indicates mobile phones affect the brain? Well, I am not on anyone’s side. And I have previously stated that eventually someone somewhere would be able to detect the effects of phones on brains, and highlighted research that might have seen such things. And if these researchers had come up with a null result, then I would still have criticised their work on exactly the same grounds! But these researchers are making an extraordinary claim – that phones affect the activity of the brain – rather mildly, but nonetheless – a real effect. To justify such an extraordinary claim, I think the researchers should have checked out these issues that I have raised. Indeed perhaps they did but had to miss them out because the paper was too long?
The authors respond .
I wrote to the lead author and asked for her comments on this article. Her colleague Dardo Tomasi replied very promptly.
I said: “However the estimation of the RF dose seems to me overly simplistic”. Dardo Tomasi said “We agree. The reasons for selecting this overly simplistic model are:”
We observed an increase in glucose metabolism when the cell phones were activated compared when the cell phones were not activated. This suggests an effect of cell phone in glucose metabolism.
- The effects were significant only in brain regions that were the crossest to the antenna and within a very narrow range of distances to the antenna (15%); no region showed significant decreases. This also suggests an effect of cell phone on glucose metabolism.
- There is no way to measure the cell phone’s RF field in the living human brain. Thus we were forced to use numerical simulations for the RF field.
- A realistic model is very complex. It depends on the assumptions about the form of the field and requires knowledge on cell phone electronics (i.e. type of antenna and RF circuitry). The electric field will also be attenuated by the tissue itself. Thus it should take into account the distribution of different tissues in the human brain, which varies from subject to subject and is difficult to calculate or even measure accurately. Furthermore, a realistic model should be based on a near field approximation of the radiation field. For all potential models the E-field decreases with distance to the antenna.
- Our data clearly shows a linear decay of glucose metabolism with distance to the antenna which strongly supports the overall conclusion that the RF fields are causing changes in metabolism in a pattern consistent with expectations, regardless of the exact functional form. This also suggests an effect of cell phone on glucose metabolism.
- For a dipole in the near field approximation the radiation field decreases as 1/r with distance to the antenna. Our over simplistic model assumed 1/r^3. We could not test differences between 1/r and 1/r^3 due to the narrow range of distances involved in the metabolic increases. In fact the radiation model fit the data as well as the simplistic model (R = 0.9 for both cases). Thus, we were not in a position that we could detect model differences and used the simplest model.
I said “Most mobile phones employ a protocol called Discontinuous Transmission (DTX) which switches off the transmission function of the phones when the phone is not required to transmit (this saves on battery life)”
- We monitored the RF transmission levels with an external antenna and with the summary report from the telephone company. For one of the subjects RF transmission was interrupted before the end of the study and the subject was removed from the study. RF transmission was not discontinued for the remaining 47 subjects during the 50 minutes of the study
I could respond to the authors comments – but I think its pretty clear that they have done their best to tie down as many aspects of this experiment as they could. It is important to bear in mind that PET – positron emission tomography – is an extremely sensitive technique which can literally ‘see people thinking’. So if any technique could detect an effect of mobile phone radiation it is quite plausible that it would require such a sensitive technique to detect it. At this point I am content to accept this as evidence that ‘something is happening’ in the region of the brain nearest the mobile phone caused by the microwave radiation from the phone. If this study is confirmed by further studies then I am sure that eventually we will find out exactly what is happening to our brains when we make a mobile phone call. And then may be will figure out if that effect could be harmful in any way.