Contralateral dominance emerges from geometric transformation in bilateral control systems

Contralateral organization is a defining feature of vertebrate nervous systems, yet its functional origin remains incompletely understood. We examined whether contralateral routing can arise as an advantageous solution in delayed bilateral control systems using a minimal computational framework.

We constructed abstract bilateral sensorimotor networks composed of sensory, central, and motor units on the left and right sides, and systematically compared alternative architectures differing in sensory laterality, commissural coupling, and local connectivity. We evaluated one-dimensional and two-dimensional models, introducing in the latter a continuous twist parameter representing transformations between sensory and motor coordinate relationships. Dense parameter scanning and bootstrap analysis were used to estimate the transition point and its robustness.

In one-dimensional models, contralateral configurations were dynamically viable but sensitive to the choice of objective function. In two-dimensional models, the twist parameter reorganized the architecture landscape: without transformation, optimal solutions were predominantly ipsilateral, whereas under strong transformation they became predominantly contralateral. Intermediate conditions exhibited an abrupt transition rather than a gradual shift. Dense parameter scanning localized this transition to a threshold at θ_c ≈ 0.483. Bootstrap analysis showed that this threshold was stable (95% CI: 0.481766-0.483507) and only weakly dependent on longitudinal delay. Objective values were minimized near and just above the transition region.

These results indicate that, within an abstract dynamical framework, contralateral routing can become advantageous under conditions of transformed sensorimotor relationships and delayed interactions.