Q. Relationship between Mind and Brain?
In modern times, before the 20th century, the most popular interpretation of the mind-brain relationship was some version of dualism. It claims that mind is essentially non-physical. The brain is the place where this nonphysical reality interacts with physical reality. The reason why you cannot "see" the mind when you inspect the brain is that the methods of inspection are adapted to the observation of material phenomena, and not to the observation of immaterial phenomena like e.g. thoughts. So what you can inspect using the methods of the natural sciences, is at most the correlates of consciousness, not the conscious itself.
In the 20th century, a series of materialist, or physicalist, alternatives to dualism have been developed. The main positions are (philosophical) behaviourism, the identity theory, functionalism and eliminativism.