Brain-computer interfaces (BCI) allow direct communication between the brain and external devices. Richard Caton discovered electrical signals on animal brains, pioneering BCI research. BCIs use brain signals like EEG to enable non-muscular communication and control. They support people with conditions like ALS and brain stem stroke by establishing real-time interaction between the user's brain and outside world independently of normal neuromuscular output. A BCI works through the interaction of the user generating intent-encoding brain signals and the BCI system translating those signals into commands that preserve the user's intent.