Mu- and beta-rhythms belong to the normal pattern of electrical brain activity in awake human beings (more). After some training, the maximum amplitude of this rhythm can be modified “by thought” (see picture) and thus used to move a cursor on a screen.
The Wadsworth BCI, set up by Jonathan Wolpaw and his colleagues at the Wadsworth Center in New York,, is one of the most sophisticated EEG-driven BCIs using mu-rhythms (more). Users with proper training (more) can achieve an information rate of about 20-25 bits/minute. Applied to a mental typewriter (more), this would result in about one word a minute, depending on the system.
It could be demonstrated that the Wadsworth BCI can be used by patients with ALS to answer yes/no-questions with high accuracy. It can also drive a Freehand-neuroprosthesis (see Graz BCI).
The BCI is usually with a cursor moving one-dimensional, but it can also be used two-dimensional with more than regions of choice for the user. See the Wadsworth-video of an individual that uses mu-rhythm to control a cursor to target at 6 different regions.