In Vivo Cortical Excitability Modulation in Major Depressive Disorder

Study objectives The aim of this study is to evaluate differences in the modulation of cortical excitability by a repetitive Transcranial Magnetic Stimulation (rTMS) protocol between patients with Major Depressive Disorder (MDD) and healthy people. The investigators hypothesize that patients with MDD exhibit less modulation of cortical excitability when compared to healthy people. In order to accomplish this goal the investigators will: * Compare measures of cortical excitability between patients with MDD and healthy individuals; * Compare the degree of modulation of cortical excitability in motor cortex after the application of rTMS, between healthy individuals and patients with MDD; * Study the progression/evolution of these measures in the group of patients with MDD after 6 weeks of antidepressant treatment, while comparing patients that respond to treatment with patients with symptoms resistant to treatment; * Analyze the relationship between cortical excitability measures and cortical excitability modulation. Study participants will perform a psychophysical task, on a computer game, in order to evaluate certain cognitive processes and understand if there are differences in performance between patients with depression and healthy subjects. Data Collection * Clinical assessment: Clinical interview will be performed with help of psychiatric, psychological and cognitive psychometric instruments (self-report questionnaires and structured interviews) to assess the participants' health. * Behavioural assessment: Participants will perform a psychophysical task in the form of a computer game. * Neurophysiological evaluation: protocol for assessing excitability and excitability modulation of the motor cortex by EMT and EMTr (ETBi). Procedures The participants recruited for the present project will be patients who are already being treated by health professionals at the Champalimaud Clinical Center, as well as healthy individuals, recruited from the nearby community. One cohort will include patients with active/symptomatic MDD and a second cohort will include patients with MDD in remission that are still in treatment. The third cohort will include a control group of healthy individuals. After they are referred to participate in this study, and if consent to participate is collected, they will be assessed to confirm their eligibility and group allocation will be performed. The study participants from all three observational groups will be submitted to (1) full clinical information assessment, (2) will be asked to perform a psychophysical task, i.e. a computer game. Finally, (3) the neurophysiological evaluation protocol will be applied. This neurophysiological evaluation protocol will be performed in two visits separated by at least 48h. This will make it possible to assess cortical excitability measures in both hemispheres independently and safely, allowing the acquisition of interhemispheric asymmetry measures. The order in which the cerebral hemispheres will be assessed will be randomized between participants. The first visit should take no longer than 120 minutes, and the second will last less than 45 minutes. Participants in the study will also be asked to come for a second study visit, to the Champalimaud Clinical Center, approximately 6 weeks after the first visit, the same study protocol will be repeated, in two consecutive sessions with the same procedures.Participants will not be rewarded monetarily; they will be supported for travel to the Clinical Center that may be necessary outside their individual clinical follow-up