Detection of mental imagery and attempted movements in patients with disorders of consciousness using EEG

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.

Keywords: EEG; attempted movements; disorders of consciousness; mental imagery; passive movements.

Figure 1

Experimental paradigm for measurements in patients. Timeline of a single trial is shown here.

Figure 2

EEG channel locations used for measurements in patients.

Figure 3

ERD/S map for the participant P2 and for the passive feet condition of the 3rd session, calculated for Laplacian channel derivations.

Figure 4

ERD/S map for the participant P1 and for the sport, and the attempted feet task of the 1st session, calculated for Laplacian channel derivations. Marked with the red circle is the Laplacian channel derivation yielding the highest accuracy, as estimated with the blockwise nested crossvalidation.

Figure 5

(A) ERD/S map for the participant P1 and for the sport task of the 2nd session. (B) LDA accuracy over trial duration for this participant, sport task, and α band during the 2nd session.