Motor imagery BCIs rely on changes in brain rhythms during imagined movement. Which option best describes this underlying signal?

• A. External auditory evoked potentials
• B. Peripheral nerve impulses
• C. Muscle fiber conduction velocity
• D. Changes in brain rhythms during imagined movement

Answer: (D)

Motor imagery BCIs rely on brain signals that reflect cortical activity when you imagine moving. The key is changes in sensorimotor rhythms captured by EEG, especially the mu (about 8–12 Hz) and beta (about 13–30 Hz) bands. When you imagine a movement, these rhythms show a reduction in power over the sensorimotor cortex, an event-related desynchronization that the system uses to infer intended action. This brain-based signal is distinct from signals outside the brain: responses to sounds (external auditory evoked potentials), impulses traveling in peripheral nerves, or muscle electrical activity (muscle fiber conduction).