This conceptual paper develops the notion of substrate–world decoupling: the possibility that conscious processing remains locally sustained by a biological brain while the subject’s perception, action, and operational life unfold through an external robotic body or a virtual avatar.The argument is grounded in complete locked-in syndrome and in existing neurotechnological research. Bidirectional brain–computer interfaces have already demonstrated elementary closed loops in which neural activity controls physical or virtual effectors and information generated by those effectors is returned to the brain as sensory experience. These experiments establish that the conscious origin of an action and the domain in which that action is realized need not coincide.The paper distinguishes between this already demonstrated elementary decoupling and the stronger future possibility of sustained virtual habitation. A sufficiently developed interface could allow a person with complete locked-in syndrome to communicate, act, interact socially, and potentially organize a continuing life within a virtual environment or through a humanoid robot, while the neural substrate sustaining consciousness remains elsewhere.This provides a constructive argument relevant to the simulation hypothesis: living, perceiving, and acting within a world does not by itself demonstrate that the process sustaining the subject is located within that same world. The paper does not claim that our universe is simulated; it establishes that such an architecture is physically coherent and already partially instantiated.