  Brain-computer interfaces (BCI) are presented as a solution for people with
global paralysis, also known as locked-in syndrome (LIS). The targeted
population includes the most severe patients, with no residual eye movements,
who cannot use any communication device (Complete LIS). However, BCI
reliability is low precisely in these cases, technical pitfalls being
considered responsible so far. Here, we propose to consider also that global
paralysis could have an impact on cognitive functions that are crucial for
being able to control a BCI. We review a bundle of arguments about the role of
motor structures in cognition. Especially, we uncover that these patients
without oculomotor activity often have injuries in more 'cognitive' structures
such as the frontal eye field or the midbrain, exposing them to cognitive
deficits further than canonical LIS population. We develop a hypothesis about
the putative role of the motor system in (covert) attention, a capacity which
is a prerequisite for most BCI paradigms and which should therefore be both
better assessed in patients and considered.
