Abstract
Background: Electroencephalogram (EEG)-based brain-computer interfaces (BCI) represent a promising component of restorative motor therapies in individuals with partial paralysis. However, in those patients, sensory functions such as proprioception are at least partly preserved. The aim of this study was to investigate whether afferent feedback interferes with the BCI-based detection of efferent motor commands during execution of movements.Methods: Brain activity of 13 able-bodied subjects (age: 29.1 ± 4.8 years; 11 males) was compared between a motor task (MT) consisting of an isometric, isotonic grip and a somatosensory electrical stimulation (SS) of the fingertips. Modulation of the mu rhythm (8–13 Hz) was investigated to identify changes specifically related to the generation of efferent commands. A linear discriminant analysis (LDA) was used to investigate the activation pattern on a single-trial basis. Classifiers were trained with MT vs. REST (periods without MT/SS) and tested with SS and vice versa to quantify the impact of afferent feedback on the classification results.Results: Few differences in the spatial pattern between MT and SS were found in the modulation of the mu rhythm. All were characterized by event-related desynchronization (ERD) peaks at electrodes C3, C4, and CP3. Execution of the MT was associated with a significantly stronger ERD in the majority of sensorimotor electrodes [C3 (p < 0.01); CP3 (p < 0.05); C4 (p < 0.01)]. Classification accuracy of MT vs. REST was significantly higher than SS vs. REST (77% and 63%; p < 10-8). Classifiers trained on MT vs. REST were able to classify SS trials significantly above chance even though no motor commands were present during SS. Classifiers trained on SS performed better in classifying MT instead of SS.Conclusion: Our results challenge the notion that the modulation of the mu rhythm is a robust phenomenon for detecting efferent commands when afferent feedback is present. Instead, they indicate that the mu ERD caused by the processing of afferent feedback generates ERD patterns in the sensorimotor cortex that are masking the ERD patterns caused by the generation of efferent commands. Thus, processing of afferent feedback represents a considerable source of false positives when the mu rhythm is used for the detection of efferent commands.
Highlights
Brain-computer interfaces (BCI) are systems that allow controlling computers or external devices directly through changes in brain activity, serving as a technical bypass for a dysfunctional neuromuscular system (Nicolas-Alonso and Gomez-Gil, 2012)
Studies have demonstrated the feasibility of BCIs to control robotic arms (Onose et al, 2012), arm orthotics (Pfurtscheller et al, 2003) combined with functional electrical stimulation (FES) (Rohm et al, 2013) or electrical wheelchairs (Galan et al, 2008) in order to compensate the loss of basic motor functions in individuals suffering from severe motor disabilities
Electrodes FP1 and F6 were excluded from the analysis completely since they exhibited extremely poor signal quality in almost all subjects and less than 50% of the data points survived preprocessing steps
Summary
Brain-computer interfaces (BCI) are systems that allow controlling computers or external devices directly through changes in brain activity, serving as a technical bypass for a dysfunctional neuromuscular system (Nicolas-Alonso and Gomez-Gil, 2012). The mu rhythm reflects the modulation or transfer of sensorimotor information in the process of motor preparation and execution (Pfurtscheller et al, 1996; McFarland et al, 2000) Likewise, it is increased during physical rest, i.e., in a state of sensorimotor cortical idling and attenuated with onset of physical activity (Kuhlman, 1978; Babiloni et al, 1999). The mu rhythm is a suitable candidate to realize natural and intuitive BCI control as it originates in the sensorimotor cortex and its modulation is directly associated with the user’s intention to perform motor actions. Electroencephalogram (EEG)-based brain-computer interfaces (BCI) represent a promising component of restorative motor therapies in individuals with partial paralysis. In those patients, sensory functions such as proprioception are at least partly preserved. The aim of this study was to investigate whether afferent feedback interferes with the BCI-based detection of efferent motor commands during execution of movements
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