American psychologist and philosopher William James remarked that: "Everyone knows that arrests of brain development occasion imbecility, that blows on the head abolish memory or consciousness, and that brain-stimulants and poisons change the quality of our ideas." However, psychology and physiology still has not been able to produce an intelligible model; of how biochemical processes could possibly be transformed into conscious experience.
James explored the various possibilities for the exact type of functional dependence between the brain and consciousness. This dependance is normally thought of as productive, in the sense that steam is produced as a function of the kettle. But this is not the only form of function that we find in nature: we also have at least two other forms of functional dependence: the permissive function, as found in the trigger of a crossbow; and the transmissive function, as of a lens or a prism. The lens or prism do not produce the light but merely transmit it in a different form.
But, a scientist never observes states of the brain producing states of consciousness. Indeed, it is not even clear what we could possibly mean by observing such production. It has been pointed out many times that there is no logical requirement that only "like can cause like" - or in other words, that only things of a similar nature can affect each other. But this consideration has not removed the mystery from the mind-body relationship. The production of consciousness by the brain, if it does in fact occur, may be as great a miracle as thought that is spontaneously generated.
Similarly, the dependence of consciousness on the brain for the manner of its manifestation in the material world; does not imply that consciousness depends upon the brain for its existence. Therefore, the brain is not an organ that generates consciousness, but rather an instrument evolved to transmit and limit the processes of consciousness and of conscious attention; so as to restrict them to those aspects of the material world which at any moment are crucial for the earthly success of the individual.