Self-organized Criticality of the Brain in Functional MRI
Self-organized criticality is a concept which was first proposed by Bak et al. (1988) in the field of physics. What is the critical state of a dynamical system? Simply describing, it can be regarded as a critical point of phase transition. You can imagine the zero degree as a critical boundary between water and ice. In this critical state, water is in the form of snowflakes, and is known to have fractal structure and self-similarity. In general, any system in the critical state exhibits fractal scaling properties. Indeed, Bak et al. proposed that the 1/f noise is a temporal sign of self-organized criticality. The concept is useful to investigate any natural or spontaneous system without any external stimulation or behavior. Let us think of the brain in resting state. If we observe the spontaneous activity of the brain in resting state, does the brain exhibit any fingerprint of self-organized criticality? The answer is 'yes'. Plenz and Thiagarajan (2007) showed spatiotemporal ...