New horizons in brain-computer interface research.

The last decade has shown a large increase in the number of P300-based BCI publications. The majority of these studies have used non-disabled subjects; far fewer studies have been conducted with people suffering from amyotrophic lateral sclerosis (ALS) or other neuromuscular disorders. Although the field has matured significantly, most research has focused on improving classification through signal processing algorithms (Hoffmann et al., 2008; Kaper et al., 2004; Lenhardt et al., 2008; Manyakov et al., 2011; Rakotomamonjy and Guigue, 2008; Serby et al., 2005), or paradigm manipulations (Frye et al., 2011; Hong et al., 2009; Jin et al., 2011; Salvaris and Sepulveda, 2009; Takano et al., 2009; Townsend et al., 2010). To be sure, signal processing and paradigm improvements are essential to increase speed and accuracy of BCI systems. Nonetheless, for the technology to be useful to people with severe communication disorders, it must be tested, and validated, by end-users. The paper published by Lulé et al. (this issue) examines BCI use in 16 control subjects and 18 disabled subjects, two with locked-in syndrome (LIS) and 16 with disorders of consciousness (DOC; i.e., unresponsive wakefulness syndrome or minimally conscious state). Extending BCI use to patients with DOC may eventually allow these patients to regain rudimentary communication. In addition, this line of research may provide insight into why people with complete locked-in syndrome (CLIS) are unable to communicate with a BCI, a question that has eluded BCI research from inception (Birbaumer, 2006; Kübler and Birbaumer, 2008; Sellers and Donchin, 2006). DOC render people immobile, possibly affecting motor pathways over time, and is potentially the most similar population to that of CLIS. Kübler and Birbaumer (2008) tested seven CLIS patients, none of whom were able to communicate with a BCI; aside from this study very few CLIS patients have been tested and these data remain unpublished. In contrast to CLIS, people with LIS retain some rudimentary ability to communicate through eye movement, or subtle muscle movements. In LIS populations, studies have shown effective communication with visual implementations of the P300 BCI paradigm (Kübler and Birbaumer, 2008; Sellers et al., 2010). Conflicting results have been shown regarding whether the severity of neuromuscular disability affects BCI performance. Kübler and Birbaumer (2008) found that remaining neuromuscular function is not related to BCI performance. Contrary to these results, Piccione et al. (2006) found that BCI performance deteriorates with greater neuromuscular disability. The differing results may be attributed to small sample size and/or individual differences. Thus, studies with much larger sample sizes are needed to begin to disambiguate this important issue.