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Medical/biological study (experimental study)

Theta-gamma coupling in hippocampus during working memory deficits induced by low frequency electromagnetic field exposure.

Published in: Physiol Behav 2017; 179: 135-142

Aim of study (acc. to author)

To examine the effects of 50 Hz and static magnetic fields on working memory and brain electrophysiology in mice.
Background/further details: Male mice were implanted with microelectrodes and behavior was assessed after three days of acclimatization. Mice with unusual behavior were excluded. Remaining mice (n=21) were divided in three groups (n=7 per group): 1) 50 Hz magnetic field exposure, 2) static magnetic field exposure and 3) sham exposure. After exposure/sham exposure, mice were subjected to a Y-maze daily. Electrophysiological recordings were performed simultaneously to behavioral examination and lasted 10 minutes.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: 2 hours/day for 7 consecutive days
Exposure 2:
Exposure duration: 2 hours/day for 7 consecutive days
General information
local geomagnetic field was approximately 0.04-0.05 mT
Exposure 1
Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 2 hours/day for 7 consecutive days
Exposure setup
Exposure source
Chamber mice were put in a pipe (8 cm length, 6 cm diameter) to prevent free moving
Setup field was created by an in-house built system consisting of a signal generator and a coil electromagnet; the solenoid coil was made from 1200 turns of copper wire (diameter of 1.01 mm) wrapped around a circular magnetic core; pipe, which contained the mouse, was kept in place with a fixing bracket
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1 mT - measured - -
Exposure 2
Main characteristics
Frequency
Type
Exposure duration 2 hours/day for 7 consecutive days
Exposure setup
Exposure source
Distance between exposed object and exposure source 10 cm
Setup permanent ferrite magnet of cylindrical shape (5 cm diameter, 3.5 cm height) was used to generate the static magnetic field
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1 mT - measured - -
Reference articles
Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated material:
Investigated organ system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

Mice exposed to the 50 Hz magnetic field for three days and longer, had a significantly impaired performance in the maze compared to the sham exposed mice: The percentage of correct choices was significantly lower and the latency was significantly longer. Additionally, the firing rate, the theta wave and gamma wave band as well as the modulation index were significantly decreased in mice exposed to the 50 Hz magnetic field for three days and longer compared to the sham exposure group. The microscopic observation revealed slight alterations in the appearence of the nuclei in the brain of 50 Hz exposed mice while sham exposed mice were histologically inconspicuous.
No differences were seen between the mice exposed to the static magnetic field and those sham exposed.
The authors suggest that there may be a negative effect of exposure to 50 Hz magnetic fields on the working memory in mice. Furthermore, they hypothesize that the abnormal spikes firing and corresponding disrupted coupling between theta wave and gamma wave band could be a potential electrophysiological mechanism for magnetic field-induced deficits in the working memory.
Study character:

Study funded by

  • Jiangsu Innovation Program for Graduate Education, China
  • Nanjing University of Aeronautics and Astronautics (NUAA), China
  • Natural Science Foundation of Jiangsu Province, China

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