Identity Under Constraint - Unihemispheric Sleep, Split-Brain Phenomena, and the limits of Localization

Theories of consciousness that locate experience in specific neural structures face a recurring empirical problem: organisms routinely maintain coherent identity and goal-directed behavior under conditions that should, on localization assumptions, abolish consciousness or split it cleanly. This paper examines two such cases—unihemispheric slow-wave sleep (USWS) in cetaceans and birds, and split-brain phenomena in commissurotomy patients—and argues that both become predictable rather than anomalous when identity is understood as maintained through constraint satisfaction rather than structural integrity. We show that USWS behaviors cannot be dismissed as reflexive automation; that dream unity in split-brain patients is better understood as retrospective reconstruction by the reporting hemisphere than as real-time global integration; and that memory consolidation proceeds through alternative pathways when canonical routes are unavailable. The framework predicts graded degradation, role reassignment under constraint, and sharp threshold failures—abrupt functional collapse when coherence costs exceed available resources, rather than proportional decline. These predictions distinguish the account from seat-based theories and expose it to empirical falsification. Beyond theoretical clarification, the framework has implications for comparative cognition, clinical assessment of disorders of consciousness, and the evaluation of identity persistence in artificial systems.