Noninvasive Communication Systems

Conditions such as amyotrophic lateral sclerosis (ALS), brainstem stroke, and severe brain or spinal cord injury can impair the neural pathways that control muscles or impair the muscles themselves. Individuals most severely affected may lose all voluntary muscle control, including eye movements and respiration, and may be completely locked in to their bodies, unable to communicate in any way. A variety of studies over the past 15 years have shown that the scalp-recorded electroencephalogram (EEG) can be used as the basis for a brain-computer interface (Wolpaw et al., 2002). BCI can provide an alternative method of communication and control for those severely affected individuals. A BCI system consists of sensors that record neural activity, signal processing that extracts features, and a translation algorithm that creates device commands to operate an external device (Wolpaw et al., 2002). The loop is completed with feedback from the external device to the BCI system user. These basic elements of a BCI communication system are illustrated in Figure 7.1. As can be seen in the figure, there is a flow of information through each of these elements which ultimately feeds back to the user. A functioning BCI system is by necessity a closed-loop, real-time system. In the case of BCI communication systems, the external device serves as a means for the user to communicate. There have been a number of BCI communication systems that have been designed to demonstrate proof of principle. These are based on a variety of neural features such as slow cortical potentials (Birbaumer et al., 1999), motor potentials (Mason et al., 2004), event-related synchronizations and desynchronizations (Pfurtscheller et al., 1993; Wolpaw et al., 1991), steady-state evoked potentials (Jones et al., 2003), and P300 potentials (Farwell and Donchin, 1988). These systems have generally used surface-recorded EEG. Noninvasive EEG recordings provide a safe alternative to invasive methods that may provide useful BCI communication devices for individuals with disabilities.