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Any movement, perception or internal cogitative activities are connected with a certain pattern of activation of neurons which interact with each other by means of electrical impulses.
A Brain-computer interface (BCI) is a new system of communication between man and machine (for example, a computer or an artificial limb), based on the direct transformation of human intentions, which are reflected in the recorded brain signals, into control commands. Over the years, attempts were made to create systems for direct interaction between the brain and external technical devices passing muscular activity which is natural for such communication. For such systems the various signals reflecting activity of a brain can be used: an electroencephalogram (EEG) Magnetoencephalography (MEG) electrocorticogram (EKoG), impulse neuronal activity and intensity of a blood-grove in the brain, etc. However, the greatest number of researches concerns the use of electrical signals. Unwieldy expensive devices are required for MEG registration. The same applies to the use of blood-grove, which is measured by functional magnetic resonance imager. That's why further only the use of electrical signals of the brain will be discussed.
BCI differs with types of registered signals of the brain and with methods their transformation in team of control of the external device. BCI, using brain potentials, which recorded on the surface of the head (EEG), are noninvasive. BCI based on the use of multiple activities of individual neurons are invasive, because this activity is logged by means of the system of microelectrodes implanted in the brain tissue. BCI based of EKoG, often called the semi-invasive, because they use potential on the brain surface as a signal, that’s they are implanted under the skull, but does not penetrate into the brain tissue. Further, BCI will be discussed further in according to this classification.
Long ago, the practical need for BCI appeared. Now tens of thousands patients are need of such interface. First of all - it's completely paralyzed people (the so-called “locked-in syndrome”), for example, some patients with ALS, the total number of which in the U.S. is up to 30 thousand people, and patients with heavy forms of cerebral paralysis, and patients with severe stroke and trauma. It is possible to expect that in process of development this technology can also be used by other patients with less damaged systems of movement, such as kvadroplegiya.
Obviously, the pattern recognition bio-potentials of the brain has to lie at the heart of BCI. If the testee is able to change the nature of his bio-potentials, for example by performing certain mental tasks, the BCI system could translate these changes in the control codes, such as the movement of the mouse cursor on a computer screen or a robotic arm manipulator. Also, these codes can be used to select letters on a "virtual keyboard" or to control the wheelchair.
The first BCI was created in the 60s at the University of California at Berkeley. It was founded on the ability to operate arbitrarily capacity of the EEG alpha rhythm. This BCI could be used to control the device with one binary command (for example, turn on / off or to answer the patient "yes / no"). However, a significant increase of researches and applications of BCI has happened in recent decades. There are scientific, technological, and social backgrounds to do this.
Last laboratory and clinical researches have expanded knowledge about the nature of brain signals used for BCI. Numerous researches have allowed allocating in the brain activity characteristic indicators, which correlate with the execution of movements, as well as the types of mental tasks performed. Thus, the types of indicators of the brain activity, potentially suitable for the construction of BCI, were isolated. Technological precondition is a creation of cheap, powerful computers and mathematical software. It allowed processing multichannel recording brain signals in real time and, accordingly to use results of processing for management of technical devices. Another technological precondition, no less important, is a creation of technological compact systems for multi-electrode registration activity of the brain. The social precondition understanding of requirement for rehabilitation of patients with various motive and neurologic violations was. For patients with impaired ability to control muscles BCI may be the only possible of communication with the outside world.