Abstract
ObjectiveOur aim was to determine if walking speed affected human sensorimotor electrocortical dynamics using mobile high-density electroencephalography (EEG).MethodsTo overcome limitations associated with motion and muscle artifact contamination in EEG recordings, we compared solutions for artifact removal using novel dual layer EEG electrodes and alternative signal processing methods. Dual layer EEG simultaneously recorded human electrocortical signals and isolated motion artifacts using pairs of mechanically coupled and electrically independent electrodes. For electrical muscle activity removal, we incorporated electromyographic (EMG) recordings from the neck into our mobile EEG data processing pipeline. We compared artifact removal methods during treadmill walking at four speeds (0.5, 1.0, 1.5, and 2.0 m/s).ResultsLeft and right sensorimotor alpha and beta spectral power increased in contralateral limb single support and push off, and decreased during contralateral limb swing at each speed. At faster walking speeds, sensorimotor spectral power fluctuations were less pronounced across the gait cycle with reduced alpha and beta power (p<0.05) compared to slower speeds. Isolated noise recordings and neck EMG spectral power fluctuations matched gait events and showed broadband spectral power increases at faster speeds.Conclusion and significanceDual layer EEG enabled us to isolate changes in human sensorimotor electrocortical dynamics across walking speeds. A comparison of signal processing approaches revealed similar intrastride cortical fluctuations when applying common (e.g. Artifact Subspace Reconstruction) and novel artifact rejection methods. Dual layer EEG, however, allowed us to document and rule out residual artifacts, which exposed sensorimotor spectral power changes across gait speeds.
Highlights
E LECTROENCEPHALOGRAPHY (EEG) is a noninvasive, lightweight and portable neuroimaging method with fast time scale for studying human electrocortical dynamics
Right sensorimotor alpha and beta power decreased during left limb swing, but increased during left limb single support and push off in double support
Electrocortical fluctuations were less pronounced across the gait cycle, with limited amplitude, duration, and spectral bandwidth compared to slow walking (Figs. 3 & 4, event related spectral perturbation (ERSP))
Summary
E LECTROENCEPHALOGRAPHY (EEG) is a noninvasive, lightweight and portable neuroimaging method with fast time scale for studying human electrocortical dynamics. Speed related changes in human electrical brain activity have been challenging to study because of motion artifact contamination at fast gait speeds [1]–[3]. Neural pathways between cortical motor planning centers and spinal cord circuits have been a source of contention [4], with gait speed changes attributed to subcortical structures that can require limited cortical input [5]. Gait speed adjustments have been studied across species using invasive recordings from cortical and subcortical structures. Separate neuronal populations were identified within pedunculopontine nucleus for controlling slow speeds and cuneiform nucleus for fast speeds. Separate gait speed control mechanisms appear to project from these structures through the brainstem via lateral paragigantocellular nucleus and to the spinal cord [5], [8], [10]
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