A minimal dynamical model linking early embryonic asymmetry to hemispheric lateralization.

Abstract

Hemispheric asymmetry is a defining feature of the human brain, yet how weak early left-right biases develop into stable hemispheric specialization remains unclear. Although molecular mechanisms establish initial embryonic asymmetries, a mechanistic explanation linking these early biases to persistent hemispheric differences has been lacking. Here we introduce a minimal dynamical model that isolates the developmental conditions under which small left-right asymmetries can be amplified and stabilized. Each hemisphere is represented by a continuous maturation variable, with reciprocal interhemispheric interactions modelled as nonlinear inhibitory coupling. Analytical stability analysis shows that hemispheric differentiation emerges when the symmetric equilibrium becomes unstable, allowing asymmetry to arise as a dynamical outcome of coupled development rather than explicit hemisphere-specific programming. Numerical simulations demonstrate that stable hemispheric asymmetry robustly emerges once interhemispheric coupling exceeds a critical threshold. Without intrinsic bias (ϵ = 0), symmetry breaking occurs through stochastic amplification, producing left- and right-dominant outcomes with approximately equal probability. Introducing a weak intrinsic bias does not create asymmetry but biases the selection among available asymmetric states. These results provide a minimal dynamical bridge linking early embryonic asymmetry to later hemispheric specialization.