Abstract
The classification of ankle movements from non-invasive brain recordings can be applied to a brain-computer interface (BCI) to control exoskeletons, prosthesis, and functional electrical stimulators for the benefit of patients with walking impairments. In this research, ankle flexion and extension tasks at two force levels in both legs, were classified from cortical current sources estimated by a hierarchical variational Bayesian method, using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) recordings. The hierarchical prior for the current source estimation from EEG was obtained from activated brain areas and their intensities from an fMRI group (second-level) analysis. The fMRI group analysis was performed on regions of interest defined over the primary motor cortex, the supplementary motor area, and the somatosensory area, which are well-known to contribute to movement control. A sparse logistic regression method was applied for a nine-class classification (eight active tasks and a resting control task) obtaining a mean accuracy of 65.64% for time series of current sources, estimated from the EEG and the fMRI signals using a variational Bayesian method, and a mean accuracy of 22.19% for the classification of the pre-processed of EEG sensor signals, with a chance level of 11.11%. The higher classification accuracy of current sources, when compared to EEG classification accuracy, was attributed to the high number of sources and the different signal patterns obtained in the same vertex for different motor tasks. Since the inverse filter estimation for current sources can be done offline with the present method, the present method is applicable to real-time BCIs. Finally, due to the highly enhanced spatial distribution of current sources over the brain cortex, this method has the potential to identify activation patterns to design BCIs for the control of an affected limb in patients with stroke, or BCIs from motor imagery in patients with spinal cord injury.
Highlights
Patients with walking impairments often use wheelchairs for transportation; this transportation means can cause pressure soars in the long-term if the patients do not perform pressure-relieving movements frequently (Stockton and Parker, 2002)
The experimental tasks consisted of isometric ankle flexion and extension at high (< ∼30% of maximum voluntary contraction level) and low force levels in each foot, yielding 8 active task conditions named “High Left Extension” (HLE), “High Left Flexion” (HLF), “High Right Extension” (HRE), “High Right Flexion” (HRF), “Low Left Extension” (LLE), “Low Left Flexion” (LLF), “Low Right Extension” (LRE), “Low Right Flexion” (LRF), and a resting control condition called “Still.” Images showing the motor tasks throughout the experiments were created in Poser 2012 (Smith Micro Software, Inc., California, United States)
variational Bayesian multimodal encephalography (VBMEG) imports the cortical model to map the estimated current dipoles, and uses the three-layer model to create a head model for improving the accuracy in the leadfield calculation
Summary
Patients with walking impairments often use wheelchairs for transportation; this transportation means can cause pressure soars in the long-term if the patients do not perform pressure-relieving movements frequently (Stockton and Parker, 2002). While invasive recordings can provide signals with high spatial resolution that allow for the decoding of more kinematic and physiological variables relevant to gait, the need for surgery limits the population that can access to this technology and, there is always a risk of infection with implanted electrodes (Lesser et al, 2010). In this sense, non-invasive BCI techniques are preferred because they are safer and patients do not need to meet strict inclusion criteria to participate in this type of BCI studies. EEG is widely used in BCIs because of its portability
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
