What is a Brain Computer Interface, explained simply
Neurons, electrodes and algorithms: how a thought becomes a command, no neuroscience degree required.
A Brain Computer Interface (BCI) is a system that lets you control a device without using your muscles, starting from the activity of the brain.
1. The brain is electric
When neurons talk to each other they produce tiny electric currents. When millions of neurons work in sync, their signal becomes strong enough to be measured from the outside, on the scalp. This technique is called electroencephalography (EEG).
2. Listening to the signal
The electrodes of an EEG headset measure voltage differences of a few microvolts, that is, millionths of a volt. The signal is extremely faint and full of noise: eye blinks, jaw movements, the mains power in your home.
3. Recognising an intention
The heart of a BCI is the software that recognises recurring patterns in the signal. Some examples:
| Paradigm | What the user does | What the software looks for |
|---|---|---|
| Motor imagery | Imagines moving a hand | Rhythm changes over the motor cortex |
| SSVEP | Looks at a flickering light | An oscillation at the same frequency |
| P300 | Waits for a rare stimulus | A peak about 300 ms after the stimulus |
4. From command to movement
Once the intention is recognised, the system sends a command to the device: a cursor, a virtual keyboard or, in SmartChair’s case, a powered wheelchair.
It is not mind reading
A BCI does not read your thoughts. It only recognises a small number of patterns that the user produces voluntarily after some training. It is a tool you learn to use, a bit like learning to drive.
In upcoming journal entries we will look at each of these steps in detail.