[ECT versus transcranial magnetic stimulation (TMS): preliminary data of computer modeling]

The essential issue of electroshock therapy (ECT) is the activity of physical stimulus, i.e., the electric current, on the disturbed structures of the brain. ECT sessions--when chronically applied for evoking antidepressive effects--are responsible for the appearance of excessive incitement in the neuronal net in the brain tissue in a form of self-sustaining after-discharge (SSAD) (convulsive attack characteristic for ECT). The study presents the computer research on basic biophysical phenomena of electroshock therapy (flow of electric current in the structures of the head just before convulsive attack). Five-layer 3-D model of the head was created in OPERA-3D (Vector Fields Ltd., Oxford), general 3 dimensional issues solver. Geometrical dimensions and electrophysical properties of each layer correspond with natural properties. The model was subjected to the action of electric stimulation (parameters identical to those applied in clinical conditions). Analysis of the flow in particular layers revealed the crawling/spreading effect present not only in the scalp layer but also in the layer of cerebrospinal fluid. The effect is conditioned by "deeper situated" lesser conduction of electricity-respectively skull bones, brain tissue. Crawling effect is the reason why only 5-15% of the electricity applied on the surface of the head reaches the surface of the brain. Electro-stimulation examinations also showed that the values of the so called density of the current in layers of brain tissue balanced between 1-10 mA/mm2. The current parameters of ECT were effective in evoking subsequent convulsive attack and safe for the brain tissue. The model was subjected to the action of magnetic stimulation according to the parameters of neurologic technique of transcranial magnetic stimulation (TMS). ELECTRA module was used to solve wire-current issues. The examination showed more regular distribution of current vectors in all layers of the head. The density of cerebral cortex was 0.1-1 mA/mm2, confirming markedly lesser current charge than that observed during ECT. The problem of magnetic stimulation efficacy in irritating deep structures of the brain demands further studies.