A brain-computer interface (BCI) is a direct communication pathway between the brain and an external device, bypassing traditional neuromuscular output. Its fundamental principle is the translation of neural activity into digital commands, creating a bridge between thought and action.

BCIs operate through a multi-stage process. First, signal acquisition records electrical brain activity, typically using non-invasive electroencephalography (EEG) caps or invasive microelectrode arrays implanted in the cortex. Next, signal processing algorithms filter out noise and isolate relevant patterns. Finally, a translation algorithm decodes these patterns into specific commands for an output device, such as a computer cursor, robotic arm, or speech synthesizer.

Current applications are primarily focused on assistive and rehabilitative technologies. They empower individuals with severe paralysis (from ALS, spinal cord injury, or stroke) to control wheelchairs, type messages, or manipulate prosthetic limbs using thought alone. BCIs are also advancing neurorehabilitation, helping retrain neural pathways after brain injury, and providing new tools for researching and treating neurological disorders like epilepsy.

The future of BCIs points toward bidirectional interfaces, which could not only read signals from the brain but also write sensory information back in, potentially restoring vision or touch.