Can there be a synergistic core emerging in the brain hierarchy to control neural activity by downward causation

Causal analysis in complex systems is inherently linked to physical reductionism, information theory, network science, and nonlinear phenomena.The relationship between Shannon information and physical causation is intensively discussed in biology, especially, in neuroscience.Causation is involved dually there.The first issue is about how neural activity in the brain causally generates conscious experience.The second issue speculates about how consciousness itself could have mental power to control the brain.Given the emergent and informational nature of consciousness, mental causation could be admissible on the two conditions: downward causation is possible, and information has causal power over and above that provided by matter.Recently, the theory of causal emergence, based on coarse-graining and partial information decomposition, suggested that synergistic information might satisfy the above conditions.Based on the Causal Equivalence Principle and the definition of multiscale modular hierarchy, this paper argues that assuming these conditions leads inevitably to overdetermination and Cartesian dualism.Instead, it is shown how nonlinear phenomena on networks and self-organization of complex hierarchical systems can arise from linear causal chains via scale transition.