Medical/biological study (experimental study)

Changes in human EEG caused by low level modulated microwave stimulation med./bio.

By: Hinrikus H, Parts M, Lass J, Tuulik V

Published in: Bioelectromagnetics 2004; 25 (6): 431-440

Aim of study (acc. to author)

To study the effects of low level microwave exposure on human EEG alpha and theta rhythms.

Background/further details

The experimental protocol consisted of one cycle of short term photic stimulation and ten cycles of the repetitive microwave stimulation.

Endpoint

effects on the neurological system: EEG

Exposure

- low level microwaves

Exposure	Parameters
Exposure 1: 450 MHz Modulation type: pulsed Exposure duration: intermittent, 60 s on/60 s off, for 20 min	power density: 0.16 mW/cm² (at the skin) SAR: 9.5 mW/kg (in the brain)

Exposure 1

Main characteristics

Frequency	450 MHz
Type	electromagnetic field
Exposure duration	intermittent, 60 s on/60 s off, for 20 min

Modulation

Modulation type	pulsed
Duty cycle	50 %
Repetition frequency	7 Hz

Exposure setup

Exposure source	quarter-wave antenna (13 cm), RF generator
Distance between exposed object and exposure source	10 cm
Chamber	The subjects lay in a dark room in a relaxed position, eyes closed and ears blocked.
Setup	The antenna was located at 10 cm from the skin on the left side of the head.
Sham exposure	A sham exposure was conducted.
Additional info	Only one EEG recording was performed for a subject per day. Test sessions were single blind, and the exposed and sham exposed subjects were randomly assigned.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
power density	0.16 mW/cm²	-	measured	-	at the skin
SAR	9.5 mW/kg	-	calculated	-	in the brain

Measurement and calculation details

The SAR calculation inside the brain was based on the field power density on the skin that was estimated from the spatial distribution measured using a field strength meter, and calibration curves obtained. (The stability of the microwave level was monitored during the experiments.) The results of numerical calculations based on the digital anatomical model taking into account the frequency dependence and possible variations of tissue dielectric value and conductivity yielded a more reliable estimation of the whole body and localized SAR than the initially used formula SAR = σE²/2ρ. The levels of power density and SAR calculated by both methods were so low that thermal effects are extremely unlikely.

Reference articles

Gajsek P et al. (2001): Parametric dependence of SAR on permittivity values in a man model

Exposed system:

human
partial body: left side of head

Methods Endpoint/measurement parameters/methodology

effects on the neurological system: EEG

Investigated system:

investigation on living organism

Investigated organ system:

brain/CNS

Time of investigation:

before exposure
during exposure
after exposure

Main outcome of study (acc. to author)

Low frequency modulated, low level microwave irradiation causes changes in the EEG rhythms' energy level. In the majority of individual cases, these changes are not statistically significant. The alterations caused by photic stimulation as well as microwave stimulation were more regular on the alpha rhythm. In the majority of cases, photic stimulation caused changes in the EEG energy level in the occipital region and microwave stimulation in the frontal region. The data demonstrated that microwave stimulation effects became apparent, starting from the third stimulation cycle. The data allowed to determine the following tendencies: 1) microwave stimulation causes an increase in the variability of the EEG energy level, 2) microwave stimulation causes changes in the frontal region in the majority of the cases, 3) repetitive exposures causes more remarkable changes in the EEG rhythms level than short term irradiation.
The physiological mechanisms underlying these effects are not well understood.

Study character:

medical/biological study
experimental study
full/main study
single blind study

Study funded by

Estonian Science Foundation (ETF), Estonia

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