Science is the study of the physical world. How then, can it be used to study the metaphysical?

Neuroscience is telling us more and more about the brain and its connection to consciousness. You can even argue that the brain causes consciousness. Psychologist can say this part of the brain is responsible for this part of consciousness. For example: The frontal lobe deals in judgments. However, we are no closer to determining what the heck consciousness is, as it cannot be seen, tasted, smelt, heard, or touched. Therefore it cannot be measured. Yet how can we continue to say we can measure these things? Have you ever weighed or measured your thoughts for your friends?