Brain–Computer Interfaces - Index of

188 F. Nijboer and U. Broermann
locked-in state might also be a result from traumatic brain-injury, hypoxia, stroke,
encephalitis, a tumor or the chronic Guillain-Barré syndrome.
Patients in the LIS state may communicate by moving their eyes or blinking.
Most patients and their caregivers use assistive communication aids which can rely
on only one remaining muscle (single switch). For example, patients control a virtual
keyboard on a computer with one thumb movement or control a cursor on a
screen with a joystick moved by the lower lip; a selection can be made (similar to
left mouse click) by blinking with the eye lid. Another useful system constitutes
of a letter matrix (see Fig. 1) which is often memorized by the patients by heart.
The caregiver serves as an interlocutor and slowly reads out loud the numbers of
the rows and the patient blinks with his eye when the row containing his desired
letter has been read. Then, the caregiver reads out loud the letters in this row until
the patient blinks again and a letter is selected. Jean Dominique Bauby, a French
journalist who entered the locked-in state after a stroke, also communicated in such
a ways, although his caregiver slowly recited the whole alphabet. His book “The
Diving Bell and the Butterfly” [20] gives a glimpse of what it is like to be locked-in
and how Bauby dealt with his condition. One quote from his book describes very
precise how coping with this physical situation may be like making a conscious
decision: “I decided to stop pitying myself. Other than my eye, two things aren’t
paralyzed, my imagination and my memory.”
Fig. 1 A letter matrix used
by many locked-in patients. A
caregiver reads out loud the
row numbers 1–5. The patient
signals a “yes” with his
remaining muscle to select a
row. The caregiver then reads
out loud the letters in that row
until the patient selects a
letter
1 A B C D E F
2 G H I J K L
3 M N O P Q R
4 S T U V W X
5 Y Z Ä Ö Ü _
However, a further stage in the ALS disease can lead to an even worse physical
situation. Some patients may enter the complete locked-in state (CLIS) and are then
totally immobile [3, 21]. These people are unable to communicate at all, because
even eye movements become unreliable and are finally lost altogether.
Let us imagine for a second that you are bedridden, speechless and immobile,
without any possibility to express your thoughts and feelings. Imagine furthermore
that this imprisonment is not temporary, but lasts for days, weeks, months and
even years – in fact for the rest of your life. A healthy brain is locked into a paralyzed
body and locked out of society by lack of communication. Brain–Computer
Interfaces may be particularly useful for these LIS and CLIS patients and bridge the
gap between inner and outer world.