When you break a bone, it’s easy to point to the problem and where to fix it. With a brain tumor, you need an image of the brain to locate it. Some tumors are harder to remove than others, but it is possible to see exactly where the trouble is. Depression, however, is different. It isn’t caused by something you can see on a scan. Instead, it comes from faulty connections that are spread diffusely throughout the brain. According to a recent study, custom-fit brain stimulation, through a technique known as transcranial direct current stimulation (tDCS) might give doctors a new tool to fine-tune the brain’s wiring.