exposures to RF fields. Dosimetric measurements for different cortical functional subregions can be conducted inside a head phantom filled with liquid having tissue-equivalent dielectric properties. A calibrated RF field scanning probe, moved by a robotic arm, records the spatial values of electric field strengths and Specific Absorption Rates (SARs) within cubic volumes in the head phantom.

It is generally recognized that the interpretation of EEG findings is difficult because of the high intra-individual variability in attention and waking state of volunteers. Some of the waking EEG studies reveal an enhancement of cortical activity, as measured by the increase of spectral power in the alpha band3 during RF exposure. Also, the most convincing effects of RF exposure on the sleep EEG indicate an increase of the power of the alpha waves, while studies on ERPs have given mixed and inconclusive results (Hamblin and Wood, 2002; Cook et al. 2006).

For other spectral ranges,4 reduction of beta band, attenuation in the theta activity, and increase of gamma response have been reported, as well as reduced amplitude and latency of N100 waves5 and an increased P300 latency.6 However, these findings could not be replicated with an experiment that had more statistical power (Hamblin et al. 2006). The inconsistency with the previous studies was attributed to the small sample size or the lack of a double blind protocol of the previous study.

Cognitive performance was assessed using several cognitive tasks, but no statistically significant effects were found on task performances in a recent study on effects on cognitive performance of exposure to 888 MHz signals using 168 volunteers (Russo et al. 2006). Another comprehensive study focused on cognitive performance of 120 subjects exposed to 900 MHz mobile phones (Keetley et al. 2006). Cognitive performance was assessed using eight cognitive tests. After adjusting for gender, age and education, simple and choice reaction times showed significant impairment, whereas performance on the trail-making task,7 which involves working memory, significantly improved.

3

The alpha band is the spectral component in the EEG signal, which falls between 8-13 Hz.

4

EEG has usually been described in terms of frequency bands: GAMMA (greater than 30Hz), BETA (13-30 Hz), ALPHA (8-13 Hz), THETA (4-8 Hz), and DELTA (less than 4 Hz).

5

N100 is an ERP component, characterized as a negative deflection in voltage, peaking approximately 100 ms after the stimulus. Anomalies in N100 may give rise to cognitive deficits (i.e., impairments of memory and learning abilities).

6

P300 is an ERP potential component, characterized as a positive deflection in voltage, peaking approximately 300 ms after the stimulus.

7

This test consists of two parts, A and B. Part A consists of encircled numbers from 1 to 25 spread across a sheet of paper. The object of the test is for the subject to connect the numbers in order, beginning with 1 and ending with 25, whereas Part B requires the subject to connect numbers and letters in an alternating pattern (1-A-2-B-3-C, etc.), both in as little time as possible.



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