Current models of brain-mind function are based, by analogy and metaphor, upon the computer sciences and the science of cybernetics. Brain processing is mental processing and mental processing is brain processing. The simple answer to this is that every finding from the neuroscience laboratories can be reasonably interpreted as supporting this one substance hypothesis. No one whose brain is being monitored by a well known acronym such as EEG, PET, MRI, or MEG can think a single thought, however spiritual, or feel an emotion, however transcendent, without associated brain activity. All mental activity is accompanied by the expenditure of real micro-joules of synaptic activity.
Mentation requires real units of electrochemical work to be done.
If the total metabolic energy of the body is taken as about 100 watts, the brain uses some 20 watts in its psycho -neuro activity. They are so united that a physiologically distressed brain results in a psychologically distressed mind and vice versa. If the primary dysfunction in either of them can be rectified then both are likely to return to normal. But an outstanding question remains unresolved. On the one hand we have the incredible monotony of traveling impulses and synaptic activity inside of a brain that is imprisoned inside of a bony box, and on the other hand we have the infinite variety of experiential reality in which we are in immediate contact with the outside world.