Objective: To investigate the relationship between physical impairment and brain–computer interface (BCI) performance.They examined 29 ALS patients (+ 6 others) who had been trained on a P300 based BCI system prior to the onset of completely locked-in syndrome. Once CLIS set in, they were no longer able to communicate using the system. Literature related to two other non-invasive techniques were used in addition to the P300 based system - low cortical potentials and sensory-motor rhythms. While performance across the board was "usable" (66% success is hardly usable, but I digress), once completely locked-in, patients' performance dropped to chance (except for one individual).
Method: We present a meta-analysis of 29 patients with amyotrophic lateral sclerosis and six patients with other severe neurological diseases in different stages of physical impairment who were trained with a BCI. In most cases voluntary regulation of slow cortical potentials has been used as input signal for BCI-control. More recently sensorimotor rhythms and the P300 event-related brain potential were recorded.
Results: A strong correlation has been found between physical impairment and BCI performance, indicating that performance worsens as impairment increases. Seven patients were in the complete locked-in state (CLIS) with no communication possible. After removal of these patients from the analysis, the relationship between physical impairment and BCI performance disappeared. The lack of a relation between physical impairment and BCI performance was confirmed when adding BCI data of patients from other BCI research groups.
Conclusions: Basic communication (yes/no) was not restored in any of the CLIS patients with a BCI. Whether locked-in patients can transfer learned brain control to the CLIS remains an open empirical question.
Significance: Voluntary brain regulation for communication is possible in all stages of paralysis except the CLIS.
I have a better hypothesis. Use of an EEG based system becomes impossible once completely locked in. EEG relies on large scale, detectable changes in millions of neurons. Locked-in syndrome likely results in large scale changes to cortical topography, due to the lack of feedback - both reinforcing and resultant - resulting in slow wave potential differences unique to this, what might be called 'normalized', state. Nevertheless, an interesting and somewhat calming idea - no pain or negativity, you just drift off into nothingness.
The logical follow-ups are to take this up and down a level. As anti-fMRI as I am (not too strongly, but I think the studies waaay overstate their significance usually), throw them in the magnet and condition different modalities on different answers. Given a multiple choice question, choice A = imagine seeing fireworks, choice B = imagine hearing a train whistle, choice C = imagine throwing a baseball, etc. Just in testing the ability to before these imagined tasks should be enough to assess their ability to respond to a command. Then to provide some very rudimentary, slow communication, use the above association technique. And by down a level, I of course mean single unit recording.
A final thought. Since language is so tightly tied to the motor system, it is possible that communication becomes obfuscated by some severe, hybrid aphasia. If that is the case, the question becomes whether consciousness relies on language. And if that is the case, how does that change the way we see animals, robots and babies (or baby animal robots!). Just something to think about the next time you hippie liberal academics are smoking up at the drum circle. :P