Major Depressive Disorder (MDD) is a condition characterized by affective, cognitive and neurovegetative symptoms. The World Health Organization (WHO) estimates a total 322 million people living with depression. Its treatment normally consists of medications such as selective serotonin reuptake inhibitors and tricyclic antidepressants. However, many cases do not respond to these drug treatments, along with their use of presenting side effects. New therapies are under investigation, such as transcranial direct current stimulation (tDCS), a safe and high tolerability procedure. It involves the passage of electric current through the brain with the purpose of altering the excitability of affected regions. Various studies have investigated the efficacy of tDCS for the treatment of MDD, with promising results stimulating the deepening of our understanding of the technique's mechanisms. The Trial of Electrical Direct-Current Therapy versus Escitalopram for Depression (ELECT-TDCS), with support of FAPESP (JP 12/20911-5), compared tDCS with escitalopram treatment (20mg/day) and placebo. Although inferior to escitalopram, tDCS was superior to placebo. A variability of its' effects on individuals, possibly related to variations of the stimulation parameters and to anatomic differences in subjects' brains was also observed. Thus, a formal quantification of the dosage of electric current that flows through the regions of interest (ROI) is wanted. Computer modeling of the spatial distribution of electric fields generated by tDCS in the patient's brain provides a method of obtaining the dosage of current through each ROI. This modeling can be done with SimNIBS, free software that displays the electric fields using realistic head models created from magnetic resonance images of each subject. It is possible, then, to establish a correlation between the clinical response to treatment with tDCS and the dosage of electric current through target brain areas. This allows for deepened investigations regarding a dose-response relation that may contribute to the efficacy of tDCS for the treatment of depression. The current study's objective is to simulate the electric fields through depressed patients' brains that have been treated with tDCS, using data already collected in ELECT-TDCS, in order to investigate a possible association between the clinical response to treatment and the electric current "dose" through each ROI during stimulation.
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