Bioelectromagnetics22:519^5282001) ElectromagneticFieldofMobilePhonesAffects VisualEventRelatedPotentialinPatientsWith Narcolepsy Robert Jech,* Karel  Sonka,Ev zen R ³ u zi cka,Antonõ  n Nebu zelsk y,Ji  rõ  BÎhm, Michaela Juklõ Â ckov a, and So na Nev sõ  malov a Department of Neurology, 1st Medical Faculty, Charles University, Prague, Czech Republic The effects of the mobile phone MP) electromagnetic ®elds on electroencephalography EEG) and event-related potentials ERP) were examined. With regard to the reported effects of MP on sleep, 22 patients with narcolepsy-cataplexy were exposed or sham exposed for 45 min to the MP 900 MHz, speci®c absorption rate 0.06 W/kg) placed close to the right ear in a double blind study. There were no changes of the EEG recorded after the MP exposure. A subgroup of 17 patients was studied on visual ERP recorded during the MP exposure. Using an adapted ``odd-ball'' paradigm, each patient was instructed to strike a key whenever rare target stimuli were presented. There were three variants of target stimuli horizontal stripes in i) left, ii) right hemi®elds or iii) whole ®eld of the screen). The exposure enhanced the positivity of the ERP endogenous complex solely in response to target stimuli in the right hemi®eld of the screen P < 0:01). The reaction time was shortened by 20 ms in response to all target stimuli P < 0:05). In conclusion, the electromagnetic ®eld of MP may suppress the excessive sleepiness and improve performance while solving a monotonous cognitive task requiring sustained attention and vigilance. Bioelectromagnetics 22:519±528, 2001. ß 2001 Wiley-Liss, Inc. Key words: GSM; cellular phones; radiotelephones; odd-ball paradigm; reaction time; EEG; sleepiness INTRODUCTION The expansion of the use of mobile phones MP) has triggered growing interest in the study of their effect on the human brain. Electroencephalography EEG) and evoked potentials can be of signi®cant use in these studies. However, data in the literature vary as to the effects of short term exposure to high frequency electromagnetic EM) ®elds. Some authors [Thuroczy et al., 1996; Eulitz et al.,1998; Krause et al., 2000] have described such effects, under speci®c conditions, on the waking EEG of healthy volunteers; others have found none at all [Roschke and Mann, 1997]. Effects on sleep have come under scrutiny repeatedly. Reite et al. [1994] described the hypnotic effects of the high frequency EM ®eld. Besides a shortened latency falling asleep and improved quality of sleep, spectral EEG changes during N-REM [Borbely et al., 1999] as well as REM sleep [Mann and Roschke, 1996] were observed. The effects of exposure to high frequency EM ®elds were used in the treatment of insomnia [Pasche et al., 1996]. Other researchers [Wagner et al., 1998] failed to prove such effects on sleep or on sleep EEG. There is scant information on the in¯uence that high frequency EM ®elds in the MP band may have on the parameters of evoked potentials. Short term exposure left both visual evoked potentials [Urban et al., 1998] and event related potentials ERP) un- affected [Eulitz et al., 1998]. The only change des- cribed so far is that of a lowering of the readiness potential amplitude under the speci®c conditions of a visual monitoring task [Freude et al., 1998]. Patients with narcolepsy fall asleep suddenly in uneventful situations, mainly during monotonous activities [ICSD, 1990]. This kind of monotonous activity may also be a stereotype cognitive task ß 2001Wiley-Liss,Inc. ÐÐÐÐÐÐ Contract grant sponsor: IGA MZ; Contract grant number: 4189-3; Contract grant sponsor: MSMT COST; Contract grant number: 244BIS.10; Contract grant sponsor: CEZ VZ; Contract grant number: J13/98 111100001. *Correspondence to: Robert Jech, M.D., Department of Neurol- ogy, 1st Medical Faculty, Charles University, Kater Ïinska  30, 120 00 Prague 2, Czech Republic. E-mail: panther@tremor.anet.cz Received for review 27 March 2000; Final revision received 16 February 2001