Abstract
Further development of an EEG based communication device for patients with disorders of consciousness (DoC) could benefit from addressing the following gaps in knowledge—first, an evaluation of different types of motor imagery; second, an evaluation of passive feet movement as a mean of an initial classifier setup; and third, rapid delivery of biased feedback. To that end we investigated whether complex and/or familiar mental imagery, passive, and attempted feet movement can be reliably detected in patients with DoC using EEG recordings, aiming to provide them with a means of communication. Six patients in a minimally conscious state (MCS) took part in this study. The patients were verbally instructed to perform different mental imagery tasks (sport, navigation), as well as attempted feet movements, to induce distinctive event-related (de)synchronization (ERD/S) patterns in the EEG. Offline classification accuracies above chance level were reached in all three tasks (i.e., attempted feet, sport, and navigation), with motor tasks yielding significant (p < 0.05) results more often than navigation (sport: 10 out of 18 sessions; attempted feet: 7 out of 14 sessions; navigation: 4 out of 12 sessions). The passive feet movements, evaluated in one patient, yielded mixed results: whereas time-frequency analysis revealed task-related EEG changes over neurophysiological plausible cortical areas, the classification results were not significant enough (p < 0.05) to setup an initial classifier for the detection of attempted movements. Concluding, the results presented in this study are consistent with the current state of the art in similar studies, to which we contributed by comparing different types of mental tasks, notably complex motor imagery and attempted feet movements, within patients. Furthermore, we explored new venues, such as an evaluation of passive feet movement as a mean of an initial classifier setup, and rapid delivery of biased feedback.
Highlights
Functional magnetic resonance imaging studies by Owen et al (2006) and others Boly et al (2007), Monti et al (2010), demonstrating detection of awareness in the unresponsive wakefulness syndrome (UWS, Laureys et al, 2010), paved the way for the development of brain–computer interfaces (BCI) as a means of communication in this patient group
Patients were asked to imagine playing tennis, or to navigate through their own apartment. Such imaginations led to very specific activations which could be used to establish a communication channel with people in the minimally conscious state (MCS, Giacino et al, 2002) by means of simple yes/no questions (Monti et al, 2010)
In both the command following and the online feedback paradigm, offline classification accuracies above chance were reached in all three tasks, with motor tasks yielding significant results more often than navigation
Summary
Functional magnetic resonance imaging (fMRI) studies by Owen et al (2006) and others Boly et al (2007), Monti et al (2010), demonstrating detection of awareness in the unresponsive wakefulness syndrome (UWS, Laureys et al, 2010), paved the way for the development of brain–computer interfaces (BCI) as a means of communication in this patient group. In these studies, patients were asked to imagine playing tennis, or to navigate through their own apartment. In a follow-up study, addressing some of the methodological challenges, EEG evidence for attempted movements to command was found in an UWS patient (Cruse et al, 2012)
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