Scientific publications
Towards improved vibro-tactile P300 BCIs
Rupert Ortner, Josep Dinarès-Ferran, Danut-Constantin Irimia and Christoph Guger
Abstract —The vibro-tactile P300 based Brain-Computer Interface is an interesting tool for severe impaired patients which cannot communicate using the muscular and visual vias. In this study we presented an improved tactile BCI for binary communication that reduces the wrong answers by adding a threshold to the decision value to achieve a valid answer, otherwise, the BCI gives an indecisive answer to the question. The threshold is calculated using a statistical test on the EEG, data recorded during the question to the patient. In total 7 tactile stimulators were placed on different parts of the subject’s body. We tried the new BCI with 4 healthy subjects and using the statistical test they were able to get no wrong answers after 10 questions asked to each participant. The spelling accuracy and information transfer rate with and without statistical test are presented as well as examples of event related potentials.
Source: Ortner, R., Dinarès-Ferran, J., Irimia, D.-C., Guger, C., 2021. Towards Improved Vibro-Tactile P300 BCIs, in: International Conference on Human-Computer Interaction. Springer, pp. 65–74. DOI: 10.1007/978-3-030-78465-2_6
Brain Computer Interface treatment for gait rehabilitation of stroke patients – Preliminary results
Marc Sebastián-Romagosa, Woosang Cho, Rupert Ortner, Christoph Guger
Abstract — Neurorehabilitation based on Brain-Computer Interfaces (BCIs) show important rehabilitation effects for patients after stroke. Previous studies have shown improvements for patients that are in a chronic stage and/or have severe hemiparesis and are particularly challenging for conventional rehabilitation techniques. Seven stroke patients in chronic phase with lower extremity hemiparesis were recruited. All of them participated in 25 BCI-sessions about 3 times/week. The BCI-system was based on the Motor Imagery (MI) of the paretic-ankle dorsiflexion and healthy-wrist dorsiflexion with Functional Electrical Stimulation (FES) and avatar feedback. Assessments were conducted to assess the changes before and after the therapy. The functional scales used were: 10-meters walking test (10MWT), Range of Motion (ROM) of the ankledorsiflexion and Timed Up and Go (TUG). Results show a significant increase in the gait speed in the primary measure 10MWT self-velocity of 0.14 m/s (SD = 0.10 This improvement is above of the minimally clinically important difference. The speed in the TUG also significantly increased by 0.08 m/s, P = 0.016. The range of motion also was increased after the therapy, ΔROM passive= 8.83° (SD = 7.22), P=0.016, and ΔROM active = 7.14° (SD = 4.84), P= 0.016. These outcomes show the feasibility of this BCI approach, and further support the growing consensus that these types of tools might develop into a new paradigm for gait rehabilitation tool for stroke patients. However, the results are from seven chronic stroke patients so the authors believe that this approach should be further validated in broader studies involving more patients.
Source: M. Sebastián-Romagosa, W. Cho, R. Ortner and C. Guger, "Brain Computer Interface treatment for gait rehabilitation of stroke patients – Preliminary results," 2021 IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2021, pp. 2948-2951, doi: 10.1109/SMC52423.2021.9659297
Auditory and Somatosensory P3 Are Complementary for the Assessment of Patients with Disorders of Consciousness
Jitka Annen, Isabella Mertel, Ren Xu, Camille Chatelle, Damien Lesenfants, Rupert Ortner 8O, Estelle A.C. Bonin, Christoph Guger, Steven Laureys and Friedemann Müller
The evaluation of the level of consciousness in patients with disorders of consciousness (DOC) is primarily based on behavioural assessments. Patients with unresponsive wakefulness syndrome (UWS) do not show any sign of awareness of their environment, while minimally conscious state (MCS) patients show reproducible but fluctuating signs of awareness. Some patients, although with remaining cognitive abilities, are not able to exhibit overt voluntary responses at the bedside and may be misdiagnosed as UWS. Several studies investigated functional neuroimaging and neurophysiology as an additional tool to evaluate the level of consciousness and to detect covert command following in DOC. Most of these studies are based on auditory stimulation, neglecting patients suffering from decreased or absent hearing abilities. In the present study, we aim to assess the response to a P3-based paradigm in 40 patients with DOC and 12 healthy participants using auditory (AEP) and vibrotactile (VTP) stimulttion. To this end, an EEG-based brain-computer interface was used at DOC patient’s bedside. We compared the significance of the P3 performance (i.e., the interpretation of significance of the evoked P3 response) as obtained by ‘direct processing’ (i.e., theoretical-based significance threshold) and ‘offline processing’ (i.e., permutation-based single subject level threshold). We evaluated whether the P3 performances were dependent on clinical variables such as diagnosis (UWS and MCS), aetiology and time since injury. Last we tested the dependency of AEP and VTP performances at the single subject level. Direct processing tends to overestimate P3 performance. We did not find any difference in the presence of a P3 performance according to the level of consciousness (UWS vs. MCS) or the aetiology (traumatic vs. non-traumatic brain injury). The performance achieved at the AEP paradigm was independent from what was achieved at the VTP paradigm, indicating that some patients performed betteroon the AEP task while others performed better on the VTP task. Our results support the importance of using multimodal approaches in the assessment of DOC patients in order to optimise the evaluation of patient’s abilities.
Source: Annen J, Mertel I, Xu R, Chatelle C, Lesenfants D, Ortner R, Bonin EAC, Guger C, Laureys S, Müller F. Auditory and Somatosensory P3 Are Complementary for the Assessment of Patients with Disorders of Consciousness. Brain Sciences. 2020; 10(10):748. https://doi.org/10.3390/brainsci10100748
EEG Biomarkers Related With the Functional State of Stroke Patients
Sebastián-Romagosa, M., Udina, E., Ortner, R., Dinarès-Ferran, J., Cho, W., Murovec, N., Matencio-Peralba, C., Sieghartsleitner, S., Allison, B.Z., Guger, C.
Introduction: Recent studies explored promising new quantitative methods to analyze electroencephalography (EEG) signals. This paper analyzes the correlation of two EEG parameters, Brain Symmetry Index (BSI) and Laterality Coefficient (LC), with established functional scales for the stroke assessment.
Methods: Thirty-two healthy subjects and thirty-six stroke patients with upper extremity hemiparesis were recruited for this study. The stroke patients where subdivided in three groups according to the stroke location: Cortical, Subcortical, and Cortical + Subcortical. The participants performed assessment visits to record the EEG in the resting state and perform functional tests using rehabilitation scales. Then, stroke patients performed 25 sessions using a motor-imagery based Brain Computer Interface system (BCI). BSI was calculated with the EEG data in resting state and LC was calculated with the Event-Related Synchronization maps.
Results: The results of this study demonstrated significant differences in the BSI between the healthy group and Subcortical group (P = 0.001), and also between the healthy and Cortical+Subcortical group (P = 0.019). No significant differences were found between the healthy group and the Cortical group (P = 0.505). Furthermore, the BSI analysis in the healthy group based on gender showed statistical differences (P = 0.027). In the stroke group, the correlation between the BSI and the functional state of the upper extremity assessed by Fugl-Meyer Assessment (FMA) was also significant, ρ = −0.430 and P = 0.046. The correlation between the BSI and the FMA-Lower extremity was not significant (ρ = −0.063, P = 0.852). Similarly, the LC calculated in the alpha band has significative correlation with FMA of upper extremity (ρ = −0.623 and P < 0.001) and FMA of lower extremity (ρ = −0.509 and P = 0.026). Other important significant correlations between LC and functional scales were observed. I addition, the patients showed an improvement in the FMA-upper extremity after the BCI therapy (ΔFMA = 1 median [IQR: 0–8], P = 0.002).
Conclusion: The quantitative EEG tools used here may help support our understanding of stroke and how the brain changes during rehabilitation therapy. These tools can help identify changes in EEG biomarkers and parameters during therapy that might lead to improved therapy methods and functional prognoses.
Source: Sebastián-Romagosa, M., Udina, E., Ortner, R., Dinarès-Ferran, J., Cho, W., Murovec, N., Matencio-Peralba, C., Sieghartsleitner, S., Allison, B.Z., Guger, C., 2020. EEG Biomarkers Related with the Functional State of Stroke Patients. Frontiers in Neuroscience 14, 582. https://doi.org/10.3389/fnins.2020.00582