Effect of magnetic field simulating electroencephalogram rhythm on memory

Mingxia GUO; Mingshi WANG; Xuemin WANG; Shunyao MA

ABSTRACT

BACKGROUND:

Recently, many researches suggest that transcranial magnetic stimulation has effect on learning and memory. Moreover, the effects of magnetic fields simulating electroencephalogram (EEG) rhythm on memory have been investigated.

OBJECTIVE:

To explore the effect of magnetic field simulating EEG rhythm on memory retrieval ability and its mechanism.

DESIGN:

Randomized controlled study.

SETTING:

Department of Medical Imaging, Tianjin Medical University,and School of Precision Instrument & Photoelectronic Engineering, Tianjin University.MATERIALS The experiment was conducted at the Electroscopic Center of TianjSn Medical University and Laboratory of Biomedical Engineering Department of Tianjin University from February 2002 to February 2004.Totally 25 Wistar rats and 5 domestic cats were selected from the Experimental Animal Center of Tianjin Medical University.

INTERVENTIONS:

All the 25 Wister rats were randomly divided into 5 group, 4 experimental groups and one control group with 5 rats in each group. Magnetic field simulating EEG rhythm was used to stimulate Wistar rats in the 4 experimental groups, but the time and frequency rate were different. Group 1 was stimulated by weak magnetic field with frequency in α rhythm (10 Hz); Group 2 was stimulated by weak magnetic field with frequency in β rhythm (20 Hz); Group 3 was stimulated by weak magnetic field with frequency changing from α to β rhythm; and Group 4 was stimulated by weak magnetic field with frequency changing from β to α rhythm. Memory retrieval ability and changes of neurotransmitters in the brain were recorded. Five cats were treated with weak magnetic field with frequency changing from α to β rhythm for 20 minutes, and the changes of EEG power spectra before and after stimulation were compared.information from long-term memory was tested with modified cross maze;hippocampus of the rats was measured with high performance liquid multiple-channel electrophysiological recording device.Comparison of memory retrieval ability Memory retrieval ability in Group 2 and Group 4 was obviously higher than that in control group 5 hours after Content ofdopamine (DA) in rats' cerebral hippocampus It was obviously higher in the 4 experimental groups than in control group [(192.72±18.66,percentage of power spectrum of β rhythm was increased after stimulation [(23.0±3.4, 14.2±1.3) %.].

CONCLUSION:

Most of the weak magnetic fields simulating EEG rhythm of human brain can decrease the retrieval of long-term memory, but magnetic field with special rhythm may increase memory retrieval ability.All the effects are related to the release of hippocampal neurotransmitters which is mediated by the change of intracellular calcium ([Ca2+]i) and synaptic vesicle.