Slow Cortical Potential Biofeedback for Verbal
Communication in Paralyzed Patients
The Thought Translation Device (TTD) is a direct connection between the brain and a computer. This interface can be used to communicate—a process referred to as "brain–computer communication" (Kübler, Kotchoubey, Kaiser, Wolpaw, & Birbaumer, 2001). Self-regulation of slow cortical potentials (SCPs) (see Neuman, Strehl, & Birbaumer, Chapter 5, and Strehl, Chapter 20, this volume) is used to control a cursor on a computer screen. Cursor movement occurs according to the alterations of the SCP amplitude. SCPs are used to control cursor movement for three reasons: First, their physiological origin is well understood; second, they are universally present in cortical cell assemblies; and, third, self-regulation of SCPs can be acquired by means of biofeedback and operant learning principles. The TTD is described in detail in this chapter. (Italics on first use of a term indicate, as in other chapters, that the term is included in the glossary at the chapter's end.)
Patients who have diseases that lead to severe or total motor paralysis are unable to communicate their needs and feelings (either orally or by keyboard) to the environment. Such patients are said to have the locked-in syndrome, a condition described impressively by JeanDominique Bauby in his famous book The Diving Bell and the Butterfly (Bauby, 1997); Bauby developed the syndrome after a stroke in the brainstem. Usually sensory and cognitive functions remain intact. Hemorrhage in the anterior brainstem (mainly in the ventral parts of pons cerebri) or nonhemorrhagic stroke in the ventral pons can cause the locked-in syndrome, which includes tetraplegia and paralysis of cranial nerves (Allen, 1993; Chia, 1991; Patterson & Grabois, 1986).