Towards a user-friendly brain-computer interface: initial tests in ALS and PLS patients

Abstract

Objective: Patients usually require long-term training for effective EEG-based brain-computer interface (BCI) control due to fatigue caused by the demands for focused attention during prolonged BCI operation. We intended to develop a user-friendly BCI requiring minimal training and less mental load.

Methods: Testing of BCI performance was investigated in three patients with amyotrophic lateral sclerosis (ALS) and three patients with primary lateral sclerosis (PLS), who had no previous BCI experience. All patients performed binary control of cursor movement. One ALS patient and one PLS patient performed four-directional cursor control in a two-dimensional domain under a BCI paradigm associated with human natural motor behavior using motor execution and motor imagery. Subjects practiced for 5-10min and then participated in a multi-session study of either binary control or four-directional control including online BCI game over 1.5-2h in a single visit.

Results: Event-related desynchronization and event-related synchronization in the beta band were observed in all patients during the production of voluntary movement either by motor execution or motor imagery. The online binary control of cursor movement was achieved with an average accuracy about 82.1+/-8.2% with motor execution and about 80% with motor imagery, whereas offline accuracy was achieved with 91.4+/-3.4% with motor execution and 83.3+/-8.9% with motor imagery after optimization. In addition, four-directional cursor control was achieved with an accuracy of 50-60% with motor execution and motor imagery.

Conclusion: Patients with ALS or PLS may achieve BCI control without extended training, and fatigue might be reduced during operation of a BCI associated with human natural motor behavior.

Significance: The development of a user-friendly BCI will promote practical BCI applications in paralyzed patients.

Fig. 1

Binary control paradigm. Subject started motor tasks of motor execution or motor imagery when they perceived the blue color text message of either ‘Yes’ or ‘No’. When the color of text message changed from blue to green, subjects sustained the motor tasks in case of ‘Yes’ or ceased the motor tasks and relaxed in case of ‘No’. EEG signal in the Detection window was extracted to determine ‘Yes’ from ERD activity or ‘No’ from ERS activity. Therefore, subjects could voluntarily make binary control of either ‘Yes’ or ‘No’ by sustaining or ceasing motor tasks time-locked to the cues.

Fig. 2

Four-directional control paradigm. Subjects started motor execution or motor imagery of right hand movement upon perceiving the blue text message of ‘RYes’ or ‘RNo’, or left hand movement when perceiving ‘LYes’ or ‘LNo’. They would continue the movement after text color change in cases of ‘RYes’ or ‘LYes’, or stop moving and relax in cases of ‘RNo’ or ‘LNo’. Computer extracted EEG signal in the Detection window and decoded ‘RYes’, ‘RNo’, ‘LYes’ and ‘LNo’ from ERD and ERS over the left hemisphere, or ERD and ERS over the right hemisphere correspondingly.

Fig. 3

Consecutive binary control and four-directional control of two-dimensional computer cursor movement: an online computer game to test the performance of binary control and four-directional control paradigms (see detail in the text).

Fig. 4

ERD and post-beta ERS activities associated with motor execution and motor imagery in binary control paradigm. Both ERD and post-beta ERS were observed in all ALS and PLS patients. For each subject, boxplots illustrate ERD (left), idle (middle) and ERS (right) activity. The difference between ERS and ERD was larger than the difference between idle state activities and ERD indicating that the proposed ERD and ERS-based BCI associated with natural motor control might provide better classification accuracy.

Fig. 5

ERD and post-beta ERS activity over left and right motor areas associated with motor execution of right and left hand movement in the four-directional control paradigm. ERD was detected over the motor area contralateral to the hand moved in both ALS1 and PLS1: ERD on the left hemisphere contralateral to right hand moved in case of ‘RYes’, and ERD on the right hemisphere contralateral to left hand moved in case of ‘LYes’. Contralateral ERS to hand moved was distinguishable in PLS1: ERSon the left hemisphere contralateral to right hand moved in case of ‘RNo’, and ERS on the right hemisphere contralateral to left hand moved in case of ‘LNo’. However, post-beta ERS in ALS1 was not recognizable.

Fig. 6

Bhattacharyya distance for selecting better spatiotemporal features for binary classification. The features with higher Bhattacharyya distance values (red color) were found in beta band over contralateral left motor areas. In motor imagery, frequency power over central-medial area also provided better separability.

Fig. 7

Bhattacharyya distance for selecting better spatiotemporal features for four-directional classification. The frequency power features over left motor areas in beta band provided better detection of ‘RYes’ and ‘RNo’ associated with right hand movement, whereas the frequency power features over right motor areas in beta band provided better detection of ‘LYes’ and ‘LNo’ associated with left hand movement.