We haven’t; we don’t know exactly what the mind is, but as exponentials noted, we’ve learned that lots of brain phenomena are correlated with mental phenomena. Strictly speaking, there isn’t a single account of what the mind is and how exactly it’s related to the brain. Some theorize that it is the brain, some theorize thar it’s produced by the brain, some theorize that it interacts with the brain, and others. There’s a lot we don’t know!