From biology to physics and the unknown: What would it mean to understand consciousness?

The three main ideas of the relation between the brain and the mind, Cartesian dualism, epiphenomenalism and brain–mind identity theory are critically reviewed. The point is made that none of these ideas, or their numerous variants, are based on explicit biological, or physical, mechanisms and are therefore not scientific in nature. By contrast, the Penrose–Hameroff orchestrated objective reduction theory does make testable biological predictions. I do not discuss the theory per se, but review two of its recent experimental tests for the purpose of urging caution in the interpretation of their results. A brief review of the neural correlates of consciousness follows. It is concluded that such experiments neither support nor falsify any of the three main ideas on the relation between brain and mind. First and foremost, science is experimental. Consequently, to bring the mind–brain problem in the realm of science requires that we directly measure conscious states the way that we measure electric current, or blood pressure, as examples. The entity of conscious state measurements will be referred to as ‘conscions’, and these must be causally linked to neural activity. If this were ever