Friday, April 1, 2011

Cell Phones & Brain Metabolism

Roughly a month ago a study was published in The Journal of the American Medical Association that reported an association between cell phone radiation and enhanced local brain glucose metabolism. Nerve cells consume glucose for their work. The study was carried carried out with great methodological expertise. The change is small and at odds the findings of other studies, including research I was involved with. I submitted a letter to the editor. It did meet the priorities. Therefore, I decided to publish it below.

To the Editor: Dr Volkow and colleagues report that a 50-minute exposure to cell phone radiation is associated with increased cerebral glucose consumption in humans.1 Inactivated phones were placed over one ear of 47 healthy volunteers, while muted phones receiving a call were placed over the other. Regional metabolic rates for glucose were measured during the last 30 minutes of the exposure with the [18F]fluorodeoxyglucose method and PET. The rates were compared to those obtained in separate imaging sessions during which both phones remained inactivated. Volkow et al1 found a statistically significant increase in metabolic rate of 2.4 μmol/100g per minute, or roughly 7%, on the side with the phone receiving the call. Frontal and parietal lobe regions were particularly affected. As the authors note, other PET studies report no change or a reduction in cerebral blood flow associated with cell phone radiation in these regions. Volkow et al1 attribute the discrepancies to methodological differences and a possible uncoupling of blood flow and glucose metabolism. Uncoupling could indicate that cell phone radiation adversely affects the brain.

My colleagues and I measured increases in metabolic rate for glucose up to 49 μmol/100g per minute, or 50%, in rodent somatic sensory cortex in response to whisker deflection2 at frequencies which were found to elevate cortical blood flow3 as well as neural spike rates.4 The observed percent change in metabolic rate is consistent with that noted in response to physiological sensory stimulation in human PET studies which Volkow et al1 discuss. Our findings suggest that the 7-fold lower percent increase in metabolic rate that Volkow et al1 found associated with cell phone radiation represents a change at which glucose consumption, blood flow and neural activity are unlikely to diverge. Therefore, the uncoupling of cerebral blood flow and glucose metabolism suggested in this study constitutes a remote possibility.

  1. Volkow ND, Tomasi D, Wang G-J et al. Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism. JAMA. 2011;305(8):808-813.
  2. Melzer P, Smith CB. Whisker follicle removal affects somatotopy and innervation of other follicles in adult mice. Cereb Cortex. 1995;5(4):301-306.
  3. Adachi K, Takahashi S, Melzer P, et al. Increases in local cerebral blood flow associated with somatosensory activation are not mediated by NO. Am J Physiol. 1994;267(6 Pt 2):H2155-H2162.
  4. Melzer P, Sachdev RN, Jenkinson N, et al. Stimulus frequency processing in awake rat barrel cortex. J Neurosci. 2006;26(47):12198-121205.