Art therapy can be used for many reasons but it tends to be one of the top methods for treating trauma survivors or people with PTSD. There are a couple theories out there. From what I've read, when someone has experienced trauma (e.g. abuse in childhood or a natural disaster, something like that) the left part of the brain (where language is) kind of dims down, making the person struggle with talking about what happened and working it out, but the right side of the brain (emotion) lights up very strongly. Art therapy allows the person a medium to "speak" about whatever happened and the emotional result of what happened because it requires use of the right side of the brain and eventually can lead to the person be more able to verbalize past trauma and talk about it.
Sorry to give a long drawn out definition, but a saw some posts asking how it could work and I'm going to school to be a therapist and plan to specialize in art therapy so I thought I would share what I know about it so far.
