Effects of electromagnetic pulses on approximate entropy of multichannel EEG in freely moving rats

To study the effects of the electromagnetic pulses (EMP) on the electrical activity of the brain, chronic electrode implantation techniques were developed to record the multichannel EEG signals, and the approximate entropy was applied to study the changes in EEG after the rats were exposed to EMP. Sixteen rats were randomly divided into 2 groups, EMP group and sham exposure group. EEG was recorded before and after EMP exposures repeatedly. ApEn was then calculated to evaluate the effects of EMP on EEG. The results showed that: (1) the ApEn of the normal EEG ranged between 0.30 and 0.71, and ApEn in different brain areas of the normal rats was not symmetrically distributed; (2) after the exposure, ApEn of the EEG in the exposed rats were significantly increased (P<0.01) except for Ch7 and Ch15. This indicated that exposed to EMP may result in the changes of the electrical activity of the brain under the given experiment conditions.