Curcio G, Ferrara M, Limongi T, Tempesta D, Di Sante G, De Gennaro L, Quaresima V, Ferrari M. Acute mobile phones exposure affects frontal cortex hemodynamics as evidenced by functional near-infrared spectroscopy. J Cereb Blood Flow Metab. Feb 25, 2009. Ahead of print.

Results of previous research indicate that brain exposure to radiofrequency electromagnetic fields (RF-EMFs) may induce an increase in regional cerebral blood flow (rCBF). Functional near-infrared spectroscopy (fNIRS) is a non-invasive and safe optical imaging technique, which allows the simultaneous acquisition of oxygenated ([O2Hb]) and deoxygenated hemoglobin ([HHb]) concentration changes. On the basis of the tight link between neuronal activity and oxygen delivery, [O2Hb] and [HHb] are considered as indicators of cortical activation. The fNIRS provides a reliable measure of brain function, as indicated by the linear relationship between hemodynamic measured by fNIRS and neural activity, as well as by the correspondence between fNIRS, functional magnetic resonance imaging, and positron emission tomography (PET) measures. These considerations justify the use of fNIRS for studying the effects of the exposure to the RF-EMFs emitted by mobile phones on cortical oxygenation.

The aim of this study was to evaluate, using fNIRS, the effects induced by an acute exposure to a GSM signal emitted by a commercially available MPs on the oxygenation of the frontal areas. The authors hypothesized that the MP exposure would induce an increased activity over the frontal areas as measured by fNIRS.

A total of 31 university students (9 male and 22 female) responded to the recruitment advertisement and agreed to fill in a questionnaire and to undergo a clinical interview to exclude any neurologic disease or psychiatric history, medication or drug intake. After this selection phase, 15 female healthy volunteers (aged between 20 and 23) were enrolled in the study. Because of data loss due to technical problems, 4 subjects were discarded and all analyses have been performed on 11 subjects. Each subject underwent two sessions (Real and Sham exposure) separated by two days, after a crossover, randomized, double-blind paradigm. The procedure lasted 60 minutes: 10-min baseline, 40-min exposure to the real signal, 10-min recovery period. The same procedure was repeated in the sham condition. A Motorola Timeport 260 mobile phone was used for generating a GSM signal with a carrier frequency of 902 MHz and a maximum value of specific absorption rate of 0.5 W/kg. An eight-channel fNIRS system was used to investigate the effect of the mobile phone emission on the frontal changes in [O2Hb] and [HHb]. In addition to frontal hemodynamic, heart rate, objective and subjective vigilance, and self-evaluation of subjective symptoms were also assessed.

Results and interpretation
It has been shown that the GSM signal emitted by a mobile phone resulted in a statistically significant linear increase in the cortical [HHb] of the frontal areas as a function of time elapsed under mobile phone exposure. No other measures showed any GSM exposure-related changes. No time-dependent increase in [HHb] was observed under the sham exposure conditions. The observed increase in [HHb] supports the notion that an acute 40-min exposure to a mobile phone emitted GSM signal affects the frontal hemodynamic, which extends the PET data received by other investigators showing a metabolic increase over the anterior regions, and provides a physiologic substratum to the attentional improvements earlier observed under GSM irradiation. The mechanism of change in [HHb] concentration is unclear. Thermal mechanism cannot be responsible for this change. Several non-thermal mechanisms have been suggested by the authors. The authors note that the short-term effects observed in this study as a result of an acute exposure preclude from conclusions regarding long-term health consequences of the RF EMF exposure. The limitations to the interpretation of the fNIRC findings include small sample size and a high inter-individual variability of the data. Such variability also depended on the long duration of the whole protocol.

This study suggests that fNIRS is a convenient tool for safe and non-invasive investigation of the cortical activation in mobile phone exposure experimental settings. The data has shown a significant bilateral increase in [HHb] over the frontal areas. The results of this study should be confirmed on a larger sample size using a multi-channel instrument that allows the investigation of a wider portion of the frontal cortex, and shorter protocols.

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