Legacy Neural Architecture and Cognitive Divergence

The human prefrontal cortex sits atop older limbic and reptilian brain structures that were not replaced but overlaid during evolutionary development — a precise instance of embedded substrate architecture. This paper proposes that ADHD and related neurodivergent profiles represent interface conflict between these substrate layers rather than pathological deficit — specifically, conflict between sequential working memory demands of the prefrontal layer and the lateral associative processing of older substrate. The consistent global prevalence of ADHD across unrelated cultures and environments is proposed as evidence that the condition reflects a structural feature of the layered neural architecture rather than a disorder of recent origin. A testable prediction follows: Diffusion Tensor Imaging should reveal measurable white matter connectivity differences between high cross-domain associative thinkers and sequential working memory dominant thinkers, constituting a structural rather than functional distinction. Institutional reward structures are identified as embedded substrate capture mechanisms that systematically disadvantage the lateral associative profile.