The pathophysiology of Major Depression Disorder (MDD) is unclear, with several theories for its neurobiological mechanisms. One possible explanation is the presence of altered neuroplasticity, which can be studied by Transcranial Magnetic Stimulation (TMS). Using TMS to study these mechanisms is performed by applying electromagnetic stimuli to the motor cortex, to obtain measures of temporary cortical excitability modulation. It is known that depressed patients with higher cortical modulation are more responsive to a TMS treatment course. However, it is unknown if there are differences in cortical modulation between depressed patients and healthy subjects. Our goal is to answer this question and contribute towards clarification of the neuroplasticity mechanisms underlying MDD. Accordingly, the investigators will access cortical excitability modulation measures in both depressed patients and healthy volunteers and compare their results. The investigators will also re-assess these measures after 6 weeks of antidepressant treatment. Finally, the investigators will study the association between cortical excitability measures and cognitive processes using an innovative cognitive task.