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IRIDIUM exposure increases c-fos expression in the mouse brain only at levels which likely result in tissue heating.

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Morrissey JJ, Raney S, Heasley E, Rathinavelu P, Dauphinee M, Fallon JH · 1999

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Brain effects from radiofrequency exposure occurred only at levels 6-30 times higher than current cell phone limits and appeared heat-related.

Plain English Summary

Summary written for general audiences

Researchers exposed mice to 1.6-GHz radiofrequency signals (similar to satellite phone frequencies) for one hour to see if it affected brain activity. They found that brain changes only occurred at exposure levels 6-30 times higher than current safety limits for cell phones, and these changes appeared to be caused by tissue heating rather than direct effects from the radiation itself.

Why This Matters

This study provides important context for understanding EMF exposure thresholds. The researchers found that neurological effects only emerged at exposure levels dramatically higher than what humans typically experience from wireless devices - specifically, 6 times the peak dose and 30 times the whole-body average of current cell phone safety limits. What's particularly significant is that the brain changes appeared to result from thermal stress (tissue heating) rather than non-thermal biological effects. This suggests the observed neurological activity was the brain's response to heat, not a direct interaction with radiofrequency energy. While this might seem reassuring, it's worth noting that this was an acute exposure study lasting just one hour. The reality is that our daily EMF exposure is chronic and cumulative, occurring over years or decades at lower levels. The science demonstrates that even sub-thermal exposures can produce biological effects over time, which this single-exposure study wouldn't capture.

Exposure Information

A logarithmic frequency spectrum from 10 Hz to 100 GHz showing where this study's 1.60 GHz exposure sits relative to common EMF sources.Where This Frequency Sits on the EMF SpectrumELFVLFLF / MFHF / VHFUHFSHFmm10 Hz100 GHzThis study: 1.60 GHzPower lines50/60 Hz5G mm28 GHzLogarithmic scale

Specific exposure levels were not quantified in this study. The study examined exposure from: 1.6-GHz Duration: 1h

Study Details

As an initial step in compiling a database for risk analysis by government agencies, the effects of 1-h exposure of mice to a 1.6-GHz radiofrequency signal, given as either a continuous wave or pulse modulated at 11 Hz with a duty cycle of 4:1 and a pulse duration of 9.2 ms IRIDIUM), on c-fos gene expression in the brain was investigated.

The IRIDIUM signal is the operating frequency for a ground-to-satellite-to-ground cellular communica...

The expression of c-fos was not significantly elevated in the brains of mice until exposure levels e...

Cite This Study
Morrissey JJ, Raney S, Heasley E, Rathinavelu P, Dauphinee M, Fallon JH (1999). IRIDIUM exposure increases c-fos expression in the mouse brain only at levels which likely result in tissue heating. Neuroscience 92(4):1539-1546, 1999.
Show BibTeX
@article{jj_1999_iridium_exposure_increases_cfos_2439,
  author = {Morrissey JJ and Raney S and Heasley E and Rathinavelu P and Dauphinee M and Fallon JH},
  title = {IRIDIUM exposure increases c-fos expression in the mouse brain only at levels which likely result in tissue heating.},
  year = {1999},
  
  url = {https://pubmed.ncbi.nlm.nih.gov/10426505/},
}
PubMed: 10426505

Cited By (26 papers)

Quick Questions About This Study

No, IRIDIUM satellite phone radiation at 1.6-GHz only caused brain changes in mice when exposure levels were 6-30 times higher than current safety limits for cell phones. At normal exposure levels, researchers found no significant effects on brain activity.
The brain changes (c-fos elevation) from 1.6-GHz IRIDIUM radiation appear caused by tissue heating rather than direct radiation effects. The pattern suggests a thermal stress response in brain regions that control temperature regulation, not direct electromagnetic interaction.
No, pulsed IRIDIUM signals and continuous wave signals at 1.6-GHz caused similar brain effects in mice. This suggests no special danger from the pulsed modulation used by IRIDIUM satellite phones compared to analog signals.
IRIDIUM radiation at 1.6-GHz must exceed six times the peak cellular phone dose and 30 times the whole-body average dose limits before causing detectable brain changes in mice. Below these levels, no significant effects occurred.
Only at extremely high exposure levels does one hour of 1.6-GHz radiation cause brain stress responses in mice. The stress appears thermal-related and occurs in brain areas controlling temperature regulation, not from direct electromagnetic effects.