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The feasibility of a brain-computer interface functional electrical stimulation system for the restoration of overground walking after paraplegia.

King CE, Wang PT, McCrimmon CM, Chou CC, Do AH, Nenadic Z - J Neuroeng Rehabil (2015)

Bottom Line: No adverse events directly related to the study were observed.Further studies are warranted to establish the generalizability of these results in a population of individuals with paraplegia due to SCI.In addition, a simplified version of the current system may be explored as a noninvasive neurorehabilitative therapy in those with incomplete motor SCI.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University of California, Los Angeles, CA, USA.

ABSTRACT

Background: Direct brain control of overground walking in those with paraplegia due to spinal cord injury (SCI) has not been achieved. Invasive brain-computer interfaces (BCIs) may provide a permanent solution to this problem by directly linking the brain to lower extremity prostheses. To justify the pursuit of such invasive systems, the feasibility of BCI controlled overground walking should first be established in a noninvasive manner. To accomplish this goal, we developed an electroencephalogram (EEG)-based BCI to control a functional electrical stimulation (FES) system for overground walking and assessed its performance in an individual with paraplegia due to SCI.

Methods: An individual with SCI (T6 AIS B) was recruited for the study and was trained to operate an EEG-based BCI system using an attempted walking/idling control strategy. He also underwent muscle reconditioning to facilitate standing and overground walking with a commercial FES system. Subsequently, the BCI and FES systems were integrated and the participant engaged in several real-time walking tests using the BCI-FES system. This was done in both a suspended, off-the-ground condition, and an overground walking condition. BCI states, gyroscope, laser distance meter, and video recording data were used to assess the BCI performance.

Results: During the course of 19 weeks, the participant performed 30 real-time, BCI-FES controlled overground walking tests, and demonstrated the ability to purposefully operate the BCI-FES system by following verbal cues. Based on the comparison between the ground truth and decoded BCI states, he achieved information transfer rates >3 bit/s and correlations >0.9. No adverse events directly related to the study were observed.

Conclusion: This proof-of-concept study demonstrates for the first time that restoring brain-controlled overground walking after paraplegia due to SCI is feasible. Further studies are warranted to establish the generalizability of these results in a population of individuals with paraplegia due to SCI. If this noninvasive system is successfully tested in population studies, the pursuit of permanent, invasive BCI walking prostheses may be justified. In addition, a simplified version of the current system may be explored as a noninvasive neurorehabilitative therapy in those with incomplete motor SCI.

No MeSH data available.


Related in: MedlinePlus

Representative space-state-time plot. The best overground walking test results (data from the 2 nd test on the 28th visit). The beginning and end of yellow blocks mark the onset of the “Walk” and “Idle” verbal cues, respectively, given by the experimenter. Red blocks represent periods when the BCI system was in the walk state; otherwise, the system is in the idle state. Green and blue blocks represent leg movements recorded by the gyroscopes. The laser signal (blue trace) represents the space-time plot, i.e. the participant’s position within the course as measured by the laser distance meter. Note that there is a delay between the onset of the “Idle” cue and the BCI idle state. This latency includes the time required for the participant’s cognitive processing and EEG to change, as well as the time required for BCI processing. The discrepancy between the onset of the idle state and gyroscope signals is due the fact that transitions from the walk to idle state can be decoded at any time during the pre-programmed 4-s step cycle. For example, if the state transition occurs during an uninterruptible leg swing, the participant will finish the leg swing despite the BCI system being in the idle state (e.g. the first green block). If, on the other hand, the state transition occurs after a leg swing, the leg will be stationary even before the system enters the idle state (e.g. the second green block). Finally, the discrepancy between the gyroscope signals and the distance meter is due to the participant only progressing when the front-wheel walker is advanced, which happens once every 4 s. Hence, all the leg movements prior to walker advancement will be registered by the gyroscope, however, they will not contribute to a position change
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Fig6: Representative space-state-time plot. The best overground walking test results (data from the 2 nd test on the 28th visit). The beginning and end of yellow blocks mark the onset of the “Walk” and “Idle” verbal cues, respectively, given by the experimenter. Red blocks represent periods when the BCI system was in the walk state; otherwise, the system is in the idle state. Green and blue blocks represent leg movements recorded by the gyroscopes. The laser signal (blue trace) represents the space-time plot, i.e. the participant’s position within the course as measured by the laser distance meter. Note that there is a delay between the onset of the “Idle” cue and the BCI idle state. This latency includes the time required for the participant’s cognitive processing and EEG to change, as well as the time required for BCI processing. The discrepancy between the onset of the idle state and gyroscope signals is due the fact that transitions from the walk to idle state can be decoded at any time during the pre-programmed 4-s step cycle. For example, if the state transition occurs during an uninterruptible leg swing, the participant will finish the leg swing despite the BCI system being in the idle state (e.g. the first green block). If, on the other hand, the state transition occurs after a leg swing, the leg will be stationary even before the system enters the idle state (e.g. the second green block). Finally, the discrepancy between the gyroscope signals and the distance meter is due to the participant only progressing when the front-wheel walker is advanced, which happens once every 4 s. Hence, all the leg movements prior to walker advancement will be registered by the gyroscope, however, they will not contribute to a position change

Mentions: Given the promising results above, the participant started the overground walking tests on visit 20 (immediately after the first suspended walking test), and continued these tests until the end of the study (visit 30). In total, 30 overground walking tests were performed over a 19-week period (see Fig. 2). Between one and six overground walking tests were performed on each visit, with each test having an average duration, written in the format mean (standard deviation), of 3.234 (0.743) min. Over time, the participant was able to perform more tests per visit (see Additional file 1). An average cross-correlation between experimenter’s verbal cues and BCI-FES response (i.e. leg movement recorded by gyroscopes, see Fig. 6 and Additional file 4) was 0.775 (0.164) with a 2.861 (4.229) s lag. Note that ∼60 % body-weight support was applied throughout these tests. This value was chosen since it approximates the contribution of the upper body in the total body weight. It was also found to be comfortable for the participant and adequate to prevent falls via the ZeroG’s fall detection algorithm.Fig. 6


The feasibility of a brain-computer interface functional electrical stimulation system for the restoration of overground walking after paraplegia.

King CE, Wang PT, McCrimmon CM, Chou CC, Do AH, Nenadic Z - J Neuroeng Rehabil (2015)

Representative space-state-time plot. The best overground walking test results (data from the 2 nd test on the 28th visit). The beginning and end of yellow blocks mark the onset of the “Walk” and “Idle” verbal cues, respectively, given by the experimenter. Red blocks represent periods when the BCI system was in the walk state; otherwise, the system is in the idle state. Green and blue blocks represent leg movements recorded by the gyroscopes. The laser signal (blue trace) represents the space-time plot, i.e. the participant’s position within the course as measured by the laser distance meter. Note that there is a delay between the onset of the “Idle” cue and the BCI idle state. This latency includes the time required for the participant’s cognitive processing and EEG to change, as well as the time required for BCI processing. The discrepancy between the onset of the idle state and gyroscope signals is due the fact that transitions from the walk to idle state can be decoded at any time during the pre-programmed 4-s step cycle. For example, if the state transition occurs during an uninterruptible leg swing, the participant will finish the leg swing despite the BCI system being in the idle state (e.g. the first green block). If, on the other hand, the state transition occurs after a leg swing, the leg will be stationary even before the system enters the idle state (e.g. the second green block). Finally, the discrepancy between the gyroscope signals and the distance meter is due to the participant only progressing when the front-wheel walker is advanced, which happens once every 4 s. Hence, all the leg movements prior to walker advancement will be registered by the gyroscope, however, they will not contribute to a position change
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4581411&req=5

Fig6: Representative space-state-time plot. The best overground walking test results (data from the 2 nd test on the 28th visit). The beginning and end of yellow blocks mark the onset of the “Walk” and “Idle” verbal cues, respectively, given by the experimenter. Red blocks represent periods when the BCI system was in the walk state; otherwise, the system is in the idle state. Green and blue blocks represent leg movements recorded by the gyroscopes. The laser signal (blue trace) represents the space-time plot, i.e. the participant’s position within the course as measured by the laser distance meter. Note that there is a delay between the onset of the “Idle” cue and the BCI idle state. This latency includes the time required for the participant’s cognitive processing and EEG to change, as well as the time required for BCI processing. The discrepancy between the onset of the idle state and gyroscope signals is due the fact that transitions from the walk to idle state can be decoded at any time during the pre-programmed 4-s step cycle. For example, if the state transition occurs during an uninterruptible leg swing, the participant will finish the leg swing despite the BCI system being in the idle state (e.g. the first green block). If, on the other hand, the state transition occurs after a leg swing, the leg will be stationary even before the system enters the idle state (e.g. the second green block). Finally, the discrepancy between the gyroscope signals and the distance meter is due to the participant only progressing when the front-wheel walker is advanced, which happens once every 4 s. Hence, all the leg movements prior to walker advancement will be registered by the gyroscope, however, they will not contribute to a position change
Mentions: Given the promising results above, the participant started the overground walking tests on visit 20 (immediately after the first suspended walking test), and continued these tests until the end of the study (visit 30). In total, 30 overground walking tests were performed over a 19-week period (see Fig. 2). Between one and six overground walking tests were performed on each visit, with each test having an average duration, written in the format mean (standard deviation), of 3.234 (0.743) min. Over time, the participant was able to perform more tests per visit (see Additional file 1). An average cross-correlation between experimenter’s verbal cues and BCI-FES response (i.e. leg movement recorded by gyroscopes, see Fig. 6 and Additional file 4) was 0.775 (0.164) with a 2.861 (4.229) s lag. Note that ∼60 % body-weight support was applied throughout these tests. This value was chosen since it approximates the contribution of the upper body in the total body weight. It was also found to be comfortable for the participant and adequate to prevent falls via the ZeroG’s fall detection algorithm.Fig. 6

Bottom Line: No adverse events directly related to the study were observed.Further studies are warranted to establish the generalizability of these results in a population of individuals with paraplegia due to SCI.In addition, a simplified version of the current system may be explored as a noninvasive neurorehabilitative therapy in those with incomplete motor SCI.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University of California, Los Angeles, CA, USA.

ABSTRACT

Background: Direct brain control of overground walking in those with paraplegia due to spinal cord injury (SCI) has not been achieved. Invasive brain-computer interfaces (BCIs) may provide a permanent solution to this problem by directly linking the brain to lower extremity prostheses. To justify the pursuit of such invasive systems, the feasibility of BCI controlled overground walking should first be established in a noninvasive manner. To accomplish this goal, we developed an electroencephalogram (EEG)-based BCI to control a functional electrical stimulation (FES) system for overground walking and assessed its performance in an individual with paraplegia due to SCI.

Methods: An individual with SCI (T6 AIS B) was recruited for the study and was trained to operate an EEG-based BCI system using an attempted walking/idling control strategy. He also underwent muscle reconditioning to facilitate standing and overground walking with a commercial FES system. Subsequently, the BCI and FES systems were integrated and the participant engaged in several real-time walking tests using the BCI-FES system. This was done in both a suspended, off-the-ground condition, and an overground walking condition. BCI states, gyroscope, laser distance meter, and video recording data were used to assess the BCI performance.

Results: During the course of 19 weeks, the participant performed 30 real-time, BCI-FES controlled overground walking tests, and demonstrated the ability to purposefully operate the BCI-FES system by following verbal cues. Based on the comparison between the ground truth and decoded BCI states, he achieved information transfer rates >3 bit/s and correlations >0.9. No adverse events directly related to the study were observed.

Conclusion: This proof-of-concept study demonstrates for the first time that restoring brain-controlled overground walking after paraplegia due to SCI is feasible. Further studies are warranted to establish the generalizability of these results in a population of individuals with paraplegia due to SCI. If this noninvasive system is successfully tested in population studies, the pursuit of permanent, invasive BCI walking prostheses may be justified. In addition, a simplified version of the current system may be explored as a noninvasive neurorehabilitative therapy in those with incomplete motor SCI.

No MeSH data available.


Related in: MedlinePlus