To study possible mechanisms how radiofrequency electromagnetic fields affect cortical activity during sleep and to test whether such effects on cortical activity during sleep interact with sleep-dependent performance changes.
Sleep-dependent performance improvements seem to be closely related to sleep spindles (12-15 Hz) and sleep slow-wave activity (0.75-4.5 Hz). In previous studies (see "related articles"), pulse modulated radiofrequency electromagnetic fields (900 MHz) were capable to modulate these EEG characteristics of sleep. A sleep spindle is a burst of oscillatory brain activity visible on an EEG that occurs during sleep stage 2. It consists of 12-14 Hz waves that occur for at least 0.5 seconds.
16 male subjects (18-21 years) underwent two experimental nights (one exposure night, one control night).
Modulation type: pulsed
|Exposure duration||intermittent during 8 h (during the sleep; exposure of 5 min "Intermittent-1" was followed by 1 min with no exposure (OFF phase), then 5 min "Intermittent-2" was followed by a 7 min OFF phase; this 18 min sequence was repeated throughout the whole night|
|Pulse width||7.1 ms|
7 consecutive 7.1 ms pulses forming one 500 ms burst; these 500 ms bursts were repeated every 4 s ("Intermittent-1" phase, 0.25 Hz, corresponding approximately to occurrence of sleep spindles), and every 1.25 s ("Intermittent-2" phase, 0.8 Hz, corresponding approximately to frequency of slow oscillations), respectively.
|SAR||0.15 W/kg||spatial average||-||10 g||peak spatial SAR during the whole night|
|SAR||10 W/kg||spatial average||-||10 g||peak spatial SAR during the 7.1 ms pulses|
|SAR||1 W/kg||-||-||-||500 ms burst average|
|SAR||0.125 W/kg||-||-||-||"Intermittent-1" average|
|SAR||0.4 W/kg||-||-||-||"Intermittent-2" average|
Good sleep quality was obtained in all subjects under both conditions (exposure and sham exposure). After pulsed radiofrequency electromagnetic field exposure an increased slow wave activity during exposure compared to sham exposure was found toward the end of the sleep period. Spindle activity was not affected. Moreover, subjects showed an increased electromagnetic field burst-related response in the slow wave activity range, indicated by an increase in event-related EEG spectral power (ERD/ERS) and phase changes (ITC) in the slow wave activity range.
Under exposure, sleep-dependent performance improvement in the motor task was reduced compared to the sham exposure condition .
The study showed that a radiofrequency electromagnetic field exposure may directly affect ongoing brain activity during sleep, and as a consequence alter sleep-dependent performance improvement.