Authors
Koivisto M, Revonsvo A, Krause C, Haarola C, Sillanmaki L, Laine M, Hamalainen H.

Forty eight healthy volunteers took part in this study. A GSM telephone was mounted to the subject's head with the earphone positioned on the left ear and the microphone orienting towards the corner of the mouth. The antenna was about 4 cm from the head, over the temporal lobe. The subjects performed tasks twice: once with and once without the RF exposure. Half of the subjects received the RF exposure in the first session and half in the second one. The subjects did not know when the phone was activated. The telephone emitted 902 MHz pulsed at a frequency of 217 Hz and with a pulse width of 577 microseconds.

The subjects performed 12 tasks. The results showed that RF exposure was associated with significantly faster response times in three of the tasks - simple reaction time, vigilance, and a mental arithmetic task.

There are some differences in the results of this study when compared with that by Preece and colleagues. The latter did not find changes in simple reaction time or vigilance. Preece, however, did find a decrease in choice reaction time, though only for an analog signal and not for a digital one.
The authors state that the results suggest that the RF emitted by GSM telephones has a facilitating effect on cognitive processing, especially in tasks that require attention or cognitive manipulation in working memory. They speculate that a possible mechanism for the effect is a slight temperature increase in brain tissue.