The Brain May Have Been Critical Before It Became Predictive: Self-Organized Criticality and the Physical Basis of Action-Readiness

Contemporary neuroscience has made remarkable progress by describing the brain in predictive, variational, and Bayesian terms. Rather than treating implementation tensions as merely technical gaps, the present paper explores a complementary possibility: the brain may be more fruitfully understood, at a foundational physical level, as a self-organizing, non-equilibrium system operating near criticality. External inputs function primarily as perturbations to an intrinsically active system, and adaptive behavior emerges when action-readiness density r(t) exceeds a transition threshold, triggering an avalanche-like shift from a metastable regime into overt action. As a first approximation, r(t) = g(t)·i(t)·m(t), where g(t), i(t), and m(t) reflect cortical gain modulation, interoceptive precision, and predictive structural coherence. Building on recent evidence that readiness-potential-like activity can arise from self-organized critical dynamics even in non-neocortical systems, the paper develops a broader physical account of action-readiness, biological plausibility, and temporal experience, and suggests an evolutionary stratification in which older transition-based dynamics provide the substrate upon which neocortical predictive processes are elaborated. Subjective time is reformulated as τ(t) ∝ 1/r(t). This paper constitutes the foundational piece (v3) of a three-paper series.