More Electrodes, Faster Minds? Rethinking Bandwidth in Brain-Computer Interfaces
High-bandwidth brain--computer interfaces (BCIs) can bypass damaged pathways, reduce motor costs, and improve communication and control. They also inspire visions of accelerated thought output, mind reading, and instant skill acquisition. This Perspective asks how gains in meaningful human I/O scale with interface capacity. We distinguish bandwidth, decodable neural states, neural states, and information a person can use, confirm, and express. Slowly updated task states can unfold into complex behavior through the body, neural control, sensory feedback, the environment, and shared context. Decodable neural activity can support prediction and control; subject-level communication depends on selection, confirmation, and authorization. On the input side, stimulation may guide plasticity and accelerate learning, while embodied skills arise through coordination of a brain, body, and environment. The scaling relationship is likely nonlinear: higher-capacity interfaces can yield real gains, while extreme increases in meaningful human I/O encounter constraints rooted in embodiment, learning, and subject expression.