The aim of this study was to test the existence of a time-course of the effects of EMFs on psychomotor (reaction times) and cognitive performance (visual search and arithmetic subtraction), and on the tympanic temperature of humans.
Twenty volunteers were randomly assigned to one of two groups. The first was exposed to a 902.4 MHz GSM signal at maximum power of 2W (estimated SAR 0.5 W/kg) for 45 minutes before the testing session. The second was exposed to the EMF during the session itself, after a 45-minute pre-exposure period. Every subject was submitted to 3 sessions in counter-balanced order, with > 48 hours between the sessions. The 3 sessions were a baseline in which the subject wore a helmet with no phone attached; a real exposure (EMF-ON); and a sham exposure (EMF-OFF). During the EMF-ON and -OFF sessions, the subjects wore a helmet in which phones were attached to each side of the head. The one on the right was to balance the weight and was never switched on.
The tasks were an acoustic simple-reaction time task, a visual search task, an arithmetic descending subtraction task, and an acoustic choice-reaction time task. They were always done in that order. Subjects were submitted to training sessions two days before the start of the experimental sessions, to reach a stable performance level.
No significant effects were seen for both speed and accuracy measures on the visual search task and descending subtraction task. However, significant effects were found for simple-reaction times for EMF-ON (a decreased time was seen), and this was significantly different for those exposed before the recording session (median =248 msecs) compared with those exposed during the session (median 334.53 msecs). A significant difference was also seen for the choice-reaction time for the EMF-On condition. There was no difference between the 2 groups, although the effect approached significance (p= 0.06).
Tympanic temperature significantly increased in the EMF-ON condition, and this was seen as a function of time, with the increase starting after 25-30 minutes of exposure.
The parallel changes of temperature and behavioural performance suggest a causal link between the two, but the authors did not find a correlation between the two. They consider that another mechanism causes the behavioural changes seen. They conclude that their results point to a specific time-course in the effects of EMFs on both brain functioning and tympanic temperature.