Some British researchers have postulated that the high incidence of automobile accidents involving cellular telephones was due to athermal effects of the cellphone's RF on the brain.

The other day I was driving home from work and got behind an SUV that was moving a bit erratically through traffic. It was going along at the speed limit and then slowed down to a crawl. Because it was an SUV, I couldn't tell if there was traffic in front of it, so I stayed behind. The SUV started to drift into the left lane and then jerked back into my lane. It went fast and then slowed for no apparent reason.

Through the back window I could see an elegantly manicured hand waving over the front passenger seat. That seemed strange, and I thought that perhaps there was a child in the seat whose mother was scolding it. Then, I looked closer and saw the driver's left hand clutching a small cellular telephone to her ear.

Apparently she was involved in an animated discussion on the phone and was the type of person who used her hands when she talked. Suddenly it dawned on me that if one hand was clutching a phone and the other hand was waving about the car wildly, there were no hands left to drive the car! I passed her quickly and got far away from her vehicle.

We all could come up with a description of the type of person who would drive like this. To me, this points to a very irresponsible person. A British scientific group, however, recently suggested another reason. They postulated that the high incidence of automobile accidents in which a cellular telephone was involved was due to an athermal effect of the phone's transmitted RF on the brain. Their claim was that brain function is retarded by electromagnetic fields, and they tested this hypothesis by studying the reaction times of people who were using cellular telephones.

Like most people, I first learned of this research from the news. According to the press, the study found that people with the type of electromagnetic exposure that occurs from cellular telephones thought more slowly.

Having learned long ago not to rely on press accounts of scientific studies, I looked a little deeper into this research. I found a set of results, summarized in the following bar chart:

Reaction time data from AW Preece, G Iwi et al: Effect of a 915-MHz simulated mobile phone signal on cognitive function in man. [Int J Radiat Biol 75:447-456, 1999.] Reproduced with permission of John Moulder, jmoulder@mcw.edu.

Reaction times are shown for seven separate reaction time tests. The "analog" signal was a 915 MHz sine wave. The "digital" signal was a 915 MHz sine wave modulated with a 217-Hz square wave at a 12.5% duty cycle. According to the authors, the analog test group for the "choice reaction time" test (marked in red) was considered to be significantly lower than the sham exposure value, but no other differences were considered to be statistically significant.

As is evident from the graph, there is a very little difference between the reaction times of volunteers who were exposed to an analog cellular telephone signal (at European frequencies), a digital cellular telephone signal, and those that were not exposed at all. A "sham exposure" means that the people being tested thought that they were being exposed but the RF was not turned on. The fact that the authors did not declare that most of the differences were statistically significant, except for the test marked in red, indicates that there was considerable variability between different subjects' responses. Also note that some of the reaction times improved for the exposed subjects.

Even if response times vary significantly, they vary by miniscule amounts: the one result that the authors felt they could trust had an average response time difference of only about 10 msec.

A more comprehensive study was performed in a similar way one year later, M Koivisto, A Revonsuo et al: Effects of 902 MHz electromagnetic field emitted by cellular telephones on response times in humans [Neuroreport 11:413-415, 2000]. When attempting to replicate the results of Preece, Koivisto found an opposite effect, which he summarized:

"With respect to behavioral consequences of the RF fields in humans, all available evidence point to the same direction: RF fields facilitate rather than disrupt performance. The physiological mechanisms underlying such influences are poorly understood, and it is too early to conclude what the significance of the observed effects is on human health.

Recently, some scientists reviewed all of the literature dealing with athermal effects, WF Pickard and EG Moros: Energy deposition processes in biological tissue: Nonthermal biohazards seem unlikely in the ultra-high frequency range [Bioelectromag 22:97-105, 2001]. After looking at all available evidence, they concluded:

"The prospects of UHF (300-3000 MHz) irradiation producing a nonthermal bioeffect are considered theoretically and found to be small... This supports previous arguments for the improbability of biological effects at UHF frequencies unless a mechanism can be found for accumulating energy over time and space and focusing it. Three possible mechanisms are then considered and shown to be unlikely... Finally, it is concluded that the rate of energy deposition from a typical fields and within a typical tissue is so small as to make unlikely any significant nonthermal biological effect.

Prior to the recent studies of human reaction times, there were a number of animal behavioral studies. Some studies showed that while exposed to RF fields the rats took longer to get through a maze than when there was no RF. Other studies of monkeys showed that they took longer to hit a feeder bar for a food reward in the presence of RF fields than before the RF was turned on. In all of these studies, the only times the RF made a difference in the animals' behavior were when the incident levels were turned very high, and the changes in behavior were attributed to heating of the brain, which is already known to affect its operation. You may have noticed from your own experience that when you have a fever you don't think very clearly.

RFI in the Brain?

Many of those who believe that RF energy can interfere with brain processes base their belief on an interference model. The brain is a huge collection of cells with electrical impulses running along them. If RF signals are captured in those cells and temporarily change voltage levels, it's easy to see how brain function could be affected. As hams, we are all familiar with different forms of Radio Frequency Interference (RFI): Television Interference (TVI), Telephone Interference (TPI), Garage Door Opener Interference (GDI) are things that we have dealt with. Why not Brainwave Interference (BWI)?

It is a compelling argument. If it's true, what do we do? Line our hats with tin foil? Connect ground straps to our feet? Attach high-pass filters from our skin to the ground? Will ferrite beads be designed into the clothing of the future?

To get a feel for how vulnerable nerve cells are to outside interference, I spoke with a colleague who studies epilepsy. Epilepsy is a disease of the brain where electrical impulses in the nerve cells occur spontaneously and form positive feedback loops, leading to an overloading of the brain with random impulses. Outwardly, this causes a seizure.

My friend studies mice to see how epilepsy forms by inducing extra electrical impulses and trying to get them to form positive feedback loops. Because brain impulses are very small, she has to perform all of her studies in a Faraday cage. She inserts microelectrodes into individual brain cells and applies electrical pulses.

When I asked her if she thought that cells picking up RF signals from the air could generate the spontaneous pulses, she laughed. Her biggest problem is that she has to directly inject current into the cells to induce pulses and is in danger of destroying the cells with too much current before a spontaneous electrical pulse forms. In her opinion, no matter how much electrical potential RF from the air generates, it could not be anywhere near what is required to generate spontaneous nerve action potentials.

Theoretically, this makes sense. Nerve cells are not wires and do not behave well as receiving antennas. In the brain, individual cells are very small. Long distances are traversed in two ways: multiple dendritic cells are connected together by synapses. Though a synapse is used to conduct electricity, it does so with chemicals so the individual dendrites do not join together to have a longer electrical length. Thus, they would have resonance at higher than even the highest microwave frequencies. Axons are much longer nerve cells, but they conduct electrical action potentials with a fairly complicated process that is based on a nonconductive myelin sheath that surrounds the cell. This setup is also unlikely to yield efficient receptors for RF.

Of course, RF usually becomes RFI only if there is something to rectify the signal. I know of no such process in biological tissue that would act as a diode to convert the very high carrier frequencies into lower modulation frequencies.

The evidence to date does not convince me that athermal exposures of RF in the head have any effect on brain function. The only confirmed effect of RF on brain function is when tissue heating takes place. The safety limits developed for ANSI/IEEE Standard C95.1-1992 avoid such heating, and as long as we follow the FCC regulations that are based on those limits, bad drivers will have to blame their problems on something else.

Editor's note: Greg Lapin, N9GL, started working in the RF safety world after spending many years first studying cardiac function imaging and then brain tumor kinetics. He serves as chairman of the ARRL RF safety Committee and as a member of the IEEE Committee on Man and Radiation. A former professor of Biomedical Engineering and Neurology at Northwestern University, Lapin now works as a consulting professional engineer in the electronics industry. He was first licensed while a teenager in 1969 and continues to be fascinated by virtually all aspects of Amateur Radio. One of his many interests is electronic design, and he is the author of Chapter 8, "Analog Signal Theory and Components" in The ARRL Handbook for Radio Amateurs. His non-ham interests include making things grow in his garden and serving as commissioner of the local children's softball league. At other times--when he is not working or helping his kids with their homework--you might find him with the local emergency services agency, climbing his tower, building a new QRP rig, playing with his APRS setup, responding to QSL cards, going off on a DXpedition, or trying to get that "new one." You can reach him by email at g.lapin@ieee.org.