What a BCI is, and what it is not
The deﬁnition of a BCI A BCI is a communication and control system that does not depend in any way on the brain’s normal neuromuscular output channels. The user’s intent is conveyed by brain signals (such as EEG) rather than by peripheral nerves and muscles, and these brain signals do not depend for their generation on neuromuscular activity. (Thus, e.g., a device that uses visual evoked potentials to determine eye-gaze direction is not a true BCI, for it relies on neuromuscular control of eye position, and simply uses the EEG as a measure of that position.) Furthermore, as a communication and control system, a BCI establishes a real-time interaction between the user and the outside world. The user receives feedback reﬂecting the outcome of the BC’Is operation, and that feedback can affect the user’s subsequent intent and its expression in brain signals. For example, if a person uses a BCI to control the movements of a robotic arm, the arm’s position after each movement is likely to affect the person’s intent for the next movement and the brain signals that convey that intent. Thus, a system that simply records and analyzes brain signals, without providing the results of that analysis to the user in an online interactive fashion, is not a BCI.
The basic design and operation of any BCI.
The fundamental principle of BCI operation
Much popular speculation and some scientiﬁc endeavors have been based on the fallacious assumption that BCIs are essentially “wire-tapping” or “mind-reading” technology, devices for listening in on the brain, detecting its intent, and then accomplishing that intent directly rather than through muscles. This misconception ignores the central feature of the brain’s interactions with the external world: that the motor behaviors that achieve a person’s intent, whether it be to walk in a certain direction, speak certain words, or play a certain piece on the piano, are acquired and maintained by initial and continuing adaptive changes in CNS function. During early development and throughout later life, CNS neurons and synapses continually change both to
acquire new behaviors and to maintain those already acquired (Salmoni et al., 1984; Ghez and Krakauer,
2000). Such CNS plasticity underlies acquisition of standard skills such as locomotion and speech and
more specialized skills as well, and it responds to and is guided by the results achieved. For example, as muscle strengths, limb lengths, and body weight change with growth and aging, the CNS adjusts its outputs so as to maintain the desired results. This dependence on initial and continuing CNS adaptation is present whether the person’s intent is accomplished in the normal fashion, that is, through peripheral nerves and muscles, or through an artiﬁcial interface, a BCI, that uses brain signals rather than nerves and muscles. BCI use depends on the interaction of two adaptive controllers: the user, who must generate brain signals that encode intent; and the BCI system, that must translate these signals into commands that accomplish the user’s
intent. Thus, BCI use is a skill that both user and system must acquire and maintain. The user must encode intent in signal features that the BCI system can measure; and the BCI system must measure these features and translate them into device commands. This dependence, both initially and continually, on the adaptation of user to system and system to user is the fundamental principle of BCI operation; and its effective management is the principal challenge of BCI research and development.