Previous studies have investigated the effects of mobile phones on the human brain and studied the changes in alpha frequency of EEG signals.5 The brain signals were acquired using a call between two mobile phone devices under predefined different conditions, i.e., right ear or left ear. The results showed that alpha activity was decreased during listening to the phone call via cellular mobile phone on the right side. However, the same practice on the left side did not modulate the alpha waves and they remained stable. The reduction in alpha activity was inversely proportional to that of cell phone radiation.
Another study investigated the EM radiation for two different types of cell phones: (1) the global system for mobile communications (GSM) and
(2) code division multiple access (CDMA). The frequency and power levels of these two communications are different. The researchers conducted the experiments on 10 participants under three different conditions: (1) before using the phone, (2) using GSM, and (3) using CDMA. The brain signals were recorded and analyzed using EEG. The results suggested that in the case of GSM the power spectral density was observed to be very high and it was concluded that GSM has a greater effect on the brain signals than CDMA.6
Hinrikus and colleagues have investigated the effects of electromagnetic field (EMF) on the human brain using EEG. Spectral power was computed on the recorded data using linear methods and it was reported that 13-31% of the subjects were affected by the EMF, depending on the modulation frequency.7
Mann et al. examined the effects of EMF on brain signals during sleep. Twelve volunteers participated in the experiments, which were composed of five stages of sleep at night and during exposure to radiofrequency (RF) emissions from a mobile phone. EEG signals were recorded and analyzed; the findings indicated that spectral power during REM sleep was increased by 5% during EMF exposure; however, no changes were reported in other sleep stages.8
Reiser and Dimpfel studied the effects of mobile phone radiation on the brain. They employed 36 participants and studied under three experimental conditions: before, during, and after the call. The findings suggested that relative alpha power during and after exposure is increased.9
In addition, Trueman et al. studied the effect of mobile phone EMF emissions on the brain using EEG signals. In their experiment, 10 volunteers participated during the presence and absence of RF. The RF was generated using two mobile technologies. In the first condition, the RF was generated by GSM phone with disabled speaker and modified to full radiation power transmission. In the second condition, the RF emissions were generated by a nonmodified GSM mobile phone in active standby mode. The participants were studied in each condition for minutes. The statistical analysis unfolded the findings, indicating a difference in the full- power mode condition within the EEG alpha (8-13 Hz) and beta (1332 Hz) bands.10
Besides, it is common practice, especially for teenagers, to use mobile devices as a replacement for alarm clocks underneath the pillow during sleep. This investigation raises concern about this practice.