LIBRARYWhat Is a Brain-Computer Interface?

A BCI turns brain activity directly into a command, with no muscles in the loop. Invasive vs non-invasive, how the read→decode→command loop works, and what's realistic.

A brain-computer interface (BCI) is a direct link from brain activity to a command. It lets you control something without moving a muscle (Wolpaw et al., 2002). Instead of your brain telling your hand to move a mouse, a BCI measures the brain signal and decodes the intent itself. That's the whole idea: measure the brain's signal, decode the intent, and act on it.

Invasive vs non-invasive BCIs

BCIs split mainly by how they read the brain. Invasive BCIs implant electrodes in or on the brain: superb signal quality and bandwidth, but they require surgery and carry medical risk. Non-invasive BCIs read from outside the head, overwhelmingly via EEG, which is safe, cheap, and accessible, at the cost of a noisier, lower-bandwidth signal. Almost everything a maker can build is non-invasive EEG.

	Invasive	Non-invasive (EEG)
Signal quality	High, close to the source	Lower, blurred by skull/scalp
Risk / access	Surgery, medical risk	Safe, no surgery, accessible
Bandwidth	High	Low (a few bits/sec)
Who uses it	Clinical / research	Makers, research, consumer

The measure-decode-command loop

Every BCI is the same loop: measure the brain signal, decode it into an intent, issue a command, and give the user feedback so they can adapt. The feedback matters as much as the decoding: users get better at producing clean, classifiable brain states by seeing the result, which is why BCIs are as much skill as they are hardware.

Fig 1

An honest look at the bandwidth

A non-invasive BCI delivers only a few bits per second, noisily. So realistic non-invasive control means a small command vocabulary (a handful of intents) often paired with a smart device that handles the fine, fast work. It's genuine control, just not high-bandwidth telepathy.

Checkpoint

Quick check

What defines a brain-computer interface (BCI)?