The brain, we argue, can be understood as a complex system or network, in which mental states emerge from the interaction between multiple physical and functional levels. Achieving further conceptual progress will crucially depend on broad-scale discussions regarding the properties of cognition and the tools that are currently available or must be developed in order to study mind–brain mechanisms

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Understanding complexity in the human brain https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3170818/