Causation, Information, and Synergy in the Multiscale Brain Hierarchy

The main aim of this paper is to introduce a theory of causation rigorously derived from physical principles and applied to multiscale biological systems. The relationship between causation and information is extensively debated in neuroscience, where causation is involved dually. The first issue concerns how neural activity in the brain causally generates conscious experience. The second issue speculates on how consciousness itself could possess mental power to control the brain. Given the emergent and informational nature of consciousness, mental causation could be admissible under two conditions: downward causation is possible, and information has causal power beyond that provided by matter. Based on the causal set approach in physics, the Causal Equivalence Principle (CEP) allows to evade both of these problems. The CEP is then generalized in terms of the continuity equation in fluid dynamics as the law of conservation of causation, which states that the flow of causation in the universe is conserved across scales. Its corollaries are: (i) there is no preferred scale of observation for causal analysis, (ii) endogenous coarse-graining of biological systems is causally legitimate, and (iii) within the spatial span of the systems, each scale has its own causal structure that cannot be derived from the causal structure at another scale. Which scale tells us the truth about what happens in the universe? The CEP provides an ontological foundation for multilevel selection in evolutionary biology. More broadly, the CEP argues for the stratification of sciences, each operating at its own scale and not reducible to a lower one.