brain–computer interface (BCI)
A brain–computer interface is a direct link between brain activity and a machine. Normally your intentions reach the world by traveling out through nerves to your muscles; a BCI taps the signal earlier, reading activity straight from the brain so it can act without that detour.
The loop has a few steps. The system records neural signals, decodes what they mean — an intended movement, a chosen letter, a mental state — and turns that into an output like a moving cursor, a robotic arm, or a typed word. Often it also shows you the result so you can adjust, closing the loop. Setups range from a non-invasive cap of scalp electrodes to fine wires implanted in the brain.
Crucially, a BCI is not mind-reading. It learns to recognize specific, trained signals — say, the pattern you produce when you imagine squeezing your hand — and reacts to those. It cannot pull out your private, unspoken thoughts; it only responds to the particular signals it was set up to detect.
A person who cannot move imagines reaching to the right; the BCI recognizes that motor pattern and slides a cursor right, letting them point and click with thought alone.
Intent in, action out — the core BCI loop.
The same idea travels under several names: brain–computer interface (BCI) and brain–machine interface (BMI) are used almost interchangeably, with BMI more common when a robotic limb is involved.