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Text is Best? Cell Phone Use and Brain Changes
Abstract & Commentary
By Russell H. Greenfield, MD, Editor
Synopsis: A small study of the effects of acute cell phone use on brain glucose metabolism revealed significant increases in areas near the location of a phone's antenna. The findings do not imply that cell phone use causes brain damage, only that the electromagnetic fields from them do cause changes in brain function.
Source: Volkow ND, et al. Effects of cell phone radiofrequency signal exposure on brain glucose metabolism. JAMA 2011;305:808-814.
Cell phone use around the globe has exploded, but not without some concerns for health and safety. Epidemiologic and human clinical studies into the effects of radiofrequency-modulated electromagnetic field (RF-EMF) exposure from cell phones have produced variable results, but it is known that these RF-EMFs are absorbed in the brain, and while the intensity of cell phone RF-EMFs is low they may still interfere with neuronal activity. The lack of clear answers regarding the impact of cell phone use on brain function and risk of malignancy apparently prompted the authors of this randomized crossover trial to further investigate the effect of acute active cell phone exposure. In particular, they focused on regional brain glucose metabolism, a marker of brain activity, as measured using PET with injection of (18F) fluorodeoxyglucose (18FDG).
Healthy subjects (n = 47) were recruited through local advertisements and screened for the absence of medical, psychiatric, or neurologic diseases. Special attention was given to ensure that participants did not abuse addictive substances (including alcohol, psychoactive drugs, and nicotine). Participants each received $250 for their participation in the study.
Cell phones were placed over each ear with microphones directed toward the participant's mouth and were secured to the head using a muffler that did not interfere with the lower part of the cell phone (where the antenna is located). All participants had two scans performed on separate days using PET with 18FDG injection. For one of the days both cell phones were turned off, while on the other day the right cell phone was both activated and receiving a call consisting of recorded text (sound was muted to avoid confounding from auditory stimulation) and the left cell phone was off. The order of conditions was randomly assigned, and participants were blinded to the condition. The mean time between the two studies was 5 days.
Activation of the right cell phone was started 20 minutes prior to 18FDG injection and maintained for 30 minutes afterward to correspond with the 18FDG uptake period. During the 50-minute session participants sat on a comfortable chair in a quiet, dimly lit room with their eyes open. A nurse was present to ensure that they kept their eyes open and did not fall asleep. At the end of the sessions, the cell phones were removed and the participants were positioned in the PET scanner.
Statistical parametric mapping was used to determine the main outcome measure of brain glucose metabolism computed as absolute metabolism (mmol/100 g per minute) and as normalized metabolism (region/whole brain).
Whole-brain glucose metabolism did not differ between conditions, which for the "off" condition corresponded to 41.2 mmol/100 g per minute (95% confidence interval [CI], 39.5-42.8) and for the on condition to 41.7 mmol/100 g per minute (95% CI, 40.1-43.3). Regional effects were significant. Specifically, comparisons on absolute metabolic measures showed significant increases (35.7 vs 33.3 mmol/100 g per minute for the "on" vs "off" conditions, respectively; mean difference, 2.4 [95% CI, 0.67-4.2]; P = 0.004) in a region that included the right orbitofrontal cortex and the lower part of the right superior temporal gyrus. No areas showed decreases. Similar results were obtained for the analysis of normalized metabolic images (normalized to whole-brain glucose metabolism), which also showed significant increases (1.048 vs 0.997 for the on vs off conditions, respectively; mean difference, 0.051 [95% CI, 0.017-0.091]; P < 0.001) in a region that included right orbitofrontal cortex and right superior temporal gyrus. Increases in brain glucose metabolism were significantly correlated with the estimated electromagnetic field amplitudes both for absolute metabolism (R = 0.95, P < 0.001) and normalized metabolism (R = 0.89; P < 0.001).
The researchers concluded that the human brain is sensitive to the effects of RF-EMFs from acute cell phone exposures. The findings of increased brain glucose metabolism in regions closest to the antenna during acute cell phone exposure suggest that brain absorption of RF-EMFs may enhance the excitability of brain tissue. They also note that this finding is of as yet unknown clinical significance.
The media pounces on stories about EMFs and possible health risks, and in at least one sense for good reason we're surrounded by them. On the other hand, there seems little we can do about it, and the stories often do little more than get us anxious. Perhaps the stories around cell phone use are different, however.
There have long been questions about the safety of prolonged exposure to EMFs, especially as relates to the development of malignancy, including cell phone use. Existing studies have left salient questions largely unanswered except to say it's probably best to use an earpiece and microphone rather than hold the phone to your ear. The present study adds fuel to that recommendation, but remains speculative.
Brain exposure to EMFs from cell phones appears to be well localized in the area of the antennae and to result in increased brain metabolic activity. The mechanisms by which this occurs have yet to be identified but may include changes in ion flux and cell membrane permeability. Even disruption of the blood brain has been posited. Beyond these hypotheses, however, lies an even greater question: How relevant are the findings? The study authors are careful to point out that their findings do not in and of themselves suggest there is damage to the brain as a result of the changes identified with acute RF-EMF exposure, only that changes do occur.
Although a small study, it raises questions about cell phone safety that need to be addressed. Until we know more, it seems prudent to recommend that our patients use headsets rather than holding the phone against their ears for long conversations.