This study is enrolling participants who are already implanted with a S-ICD device (Subcutaneous Implantable Cardioverter Defibrillator, which is a device designed to monitor heart rhythms and deliver a shock to the heart to stop life threatening heart rhythms), and are undergoing a routine outpatient clinic follow up appointment to have their S-ICD checked. The aim of the study is to see if a feature in the device can recognize muscle movement and differentiate movement from irregular heart signals. The study involves doing some simple arm exercises while collecting device data, both with this feature turn on and then with it turned off. Participants will be randomized to either have the feature turned on or off initially then it will be programmed the alternative way and the same exercise testing will be repeated. The study will involve just one visit.

The purpose of this study is to use magnetic resonance imaging (MRI) to take images of a participant's brain, and then apply an investigational way of processing the image, called Individualized Network-based Single-frame Coactivation Pattern Estimation ("INSCAPE") to measure participant's brain activity. This method uses a computer program to understand which parts of the brain communicate with each other and creates a map of the brain areas that are connected.

Participants being recruited in this study will include people planning to receive Transcranial Magnetic Stimulation ("TMS") for Major Depressive Disorder ("MDD"). Healthy participants are also being recruited. Images taken of depressed participants' brains will be compared to images of non-depressed participants' brains. Participation in this study will require three visits in which you will undergo MRI scans. The interval between each visits is about 3 weeks. Depressed participants will also complete mood assessments at several different intervals while they are receiving TMS for depression.

During each visit, MRI scans will require about 30 minutes of time in total. During the MRI scan, participants will need to stay still, relax, and keep eyes open in the scanner.