Study On The Focality Of The Electric Field In The Human Brain In TDCS

Transcranial direct current stimulation(tDCS) technology is mainly used to stimulate some nerve nucleus in human brain by injecting current through electrodes placed in specific locations on human head, so as to achieve the treatment of psychiatric and neurological diseases. In this dissertation, we study the relationship between the focality of the electric field and the electrode parameters in the three-sphere head model using ANSYS software.Firstly, different areas of electrodes have great influences on the distribution of the electric field in the brain. In this dissertation, a three-sphere head model is established and the electrodes were placed on the scalp surface in classical tDCS positions. By comparing with the literatures, we verify that it is reliable to use ANSYS software for tDCS stimulation research. By respectively fixing cathode or anode electrode areas at 25cm2, we change the corresponding electrode areas from a minimum of 1cm2 to a maximum of 45cm2. Then we study the influence of the electrode areas on the spatial distributions of the electric field in the brain model. As a result, the relationship curves between the current density, electric field and the electrode areas are achieved.Secondly, the uniform cylindrical electrode is used to study the relationship between the electrode positions and the spatial electric field distributions in the brain model. We select three electrodes to study the relationship, which include one anode electrode injected with 2mA current and two cathodes injected with-1mA current, respectively. Changing the rotation angle α from 15° to 75°, we get the distributions of electric field in the head model. Results show that when the α becomes smaller, the current density and electric field at the target location will increase and the stimulated target volume will decrease. On the contrary, when the α becomes lager, the current density and electric field at the target location will decrease and the stimulated target volume will increase.Lastly, the focality of the electric field in the target area is improved by using multiple electrodes. Five electrodes, including one anode and four cathodes, are placed on the surface of the scalp. They are divided into two groups for two cases. The single anode is injected with 2mA current and other cathodes are injected with-0.5mA current. Then we study the electric field distributions in the head model. It is shown that for the second case the focality is better: ratio of the stimulated brain volume to the whole brain model volume(RA) is only 8.59%, which is 4.19% lower than that of the classic method. The current density and electric field at the motor cortex target point are respectively 0.239A/m2 and 0.531V/m, the current density and electric field at the target point M1 apb are 0.133A/m2 and 0.296V/m, respectively. Results show that the current density and electric field at the two points are higher than the classical method.For the first case, the stimulation effect is slightly inferior to the second one.Results of this dissertation provide a good method for the study of the focality in tDCS. By injecting different currents with different electrode configurations, we get good focality in the target area in the head model, which will also provide some reference and help for the further study on the improving the focality of the electric field in the brain.