20 healthy volunteers (7 males, 13 females) who were participants in the previous study were retested and underwent an adaptation night followed by two experimental nights in which they were randomlyexposed to two conditions (active and sham exposure), followed by a full-night sleep episode. Participants were divided into two groups based on the data of the previous experiment: "increaser" group and "decreaser" group according to an increase/decrease in spectralpower in the 11.5-12.25 Hzfrequency range during non-REM sleep.
mobile phone attached to an adjustable head cradle which was worn by the test person during exposure; phone positioned over the right temporal region and adjusted towards the corner of the mouth, comparable to normal use; ear plug placed in the test person's right ear; audio circuits of the phone disconnected, a padding placed between the handset and its cover, and phone set to send with maximum power
No significant change in power was observed between the active and sham exposure conditions in the 12.25-13.5 Hz and 13.5-14 Hzfrequency ranges, either overall, or between the "increaser" group and the "decreaser" group. No significant change was found between the active exposure and sham exposure for either sleeplatency, REM sleeplatency, sleep duration, sleep efficiency, number of arousals and Karolinska Sleepiness Scale score. However, the EEGspectralpower was increased in the 11.5-12.25 Hzfrequency range in the first 30 min of non-REM sleep following active exposure. This increase was more prominent in the participants that showed an increase in the original study ("increaser" group). These data confirm the previous findings of mobile phone-like emissions affecting the EEG during non-REM sleep (see above). Importantly, this low-level effect was also shown to be sensitive to individual variability. Furthermore, this indicates that previous negative results are not strong evidence for a lack of an effect and, given the far-reaching implications of mobile phone research, the authors conclude that it may need to rethink the interpretation of results and the manner in which research is conducted in this field.