Electrocortical correlates of human level-ground, slope, and stair walking

Abstract

This study investigated electrocortical dynamics of human walking across different unconstrained walking conditions (i.e., level ground (LW), ramp ascent (RA), and stair ascent (SA)). Non-invasive active-electrode scalp electroencephalography (EEG) signals were recorded and a systematic EEG processing method was implemented to reduce artifacts. Source localization combined with independent component analysis and k-means clustering revealed the involvement of four clusters in the brain during the walking tasks: Left and Right Occipital Lobe (LOL, ROL), Posterior Parietal Cortex (PPC), and Central Sensorimotor Cortex (SMC). Results showed that the changes of spectral power in the PPC and SMC clusters were associated with the level of motor task demands. Specifically, we observed α and β suppression at the beginning of the gait cycle in both SA and RA walking (relative to LW) in the SMC. Additionally, we observed significant β rebound (synchronization) at the initial swing phase of the gait cycle, which may be indicative of active cortical signaling involved in maintaining the current locomotor state. An increase of low γ band power in this cluster was also found in SA walking. In the PPC, the low γ band power increased with the level of task demands (from LW to RA and SA). Additionally, our results provide evidence that electrocortical amplitude modulations (relative to average gait cycle) are correlated with the level of difficulty in locomotion tasks. Specifically, the modulations in the PPC shifted to higher frequency bands when the subjects walked in RA and SA conditions. Moreover, low γ modulations in the central sensorimotor area were observed in the LW walking and shifted to lower frequency bands in RA and SA walking. These findings extend our understanding of cortical dynamics of human walking at different level of locomotion task demands and reinforces the growing body of literature supporting a shared-control paradigm between spinal and cortical networks during locomotion.

Dynamics of corticospinal motor control during overground and treadmill walking in humans

“…As such, ERS and ERD reflect an induced response of ongoing activity rather than an additive response and would hence not be accompanied by phase locked activity (Tallon-Baudry et al 1996). As the changes in spectral power observed here closely resemble those previously reported in ambulatory EEG studies (Artoni et al 2017; Bradford et al 2016; Bruijn et al 2015; Bulea et al 2015; Cheron et al 2012; Gwin et al 2011; Knaepen et al 2015; Luu et al 2017; Oliveira et al 2017b; Severens et al 2012), this may require a broader reinterpretation of the cortical dynamics during walking.…”

“…The cortical power fluctuations during overground and treadmill walking observed in this study closely resemble those previously reported in ambulatory EEG studies conducted on a treadmill. A number of studies found increased power over sensorimotor cortical areas at the end of stance and during double support, and decreased power during the swing/single support phase (Artoni et al 2017; Bradford et al 2016; Bruijn et al 2015; Bulea et al 2015; Cheron et al 2012; Gwin et al 2011; Knaepen et al 2015; Luu et al 2017; Oliveira et al 2017b; Severens et al 2012). Notably, one previous study (Bulea et al 2015) reported similar changes in cortical power to those in the current study during walking on a user-driven treadmill, a condition which simulates overground walking more closely than walking on a standard, motorized treadmill.…”

“…In recent years ambulatory electroencephalography (EEG) has been increasingly used to investigate cortical and corticospinal sensorimotor processes during walking in humans (Artoni et al 2017; Bradford et al 2016; Bruijn et al 2015; Bulea et al 2015; Gwin et al 2011; Knaepen et al 2015; Luu et al 2017; Oliveira et al 2017b; Petersen et al 2012; Seeber et al 2014; Seeber et al 2015; Severens et al 2012; Sipp et al 2013; Storzer et al 2016; Wagner et al 2016; Wagner et al 2012; Wagner et al 2014; Winslow et al 2016). Time-frequency analysis revealed that cortical oscillations and corticospinal interactions are modulated relative to the gait cycle at theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz) and gamma (>30 Hz) frequencies.…”

Influence of Mismarking Fiducial Locations on EEG Source Estimation

“…One interesting finding was that the largest maximum distances, among the three ICs of interest, occurred in the primary somatosensory cortex, which is an area frequently discussed in the EEG studies related to walking [8,9]. A previous study found that tangential sources near the boundary of the cortex were more sensitive to electrode location errors, which could explain the larger maximum distances for the dipole at the primary somatosensory cortex compared to a dipole deeper within the cortex such as the anterior cingulate [5].…”

“…We analyzed the influence of the fiducial shifts on all twenty-three ICs but picked three to illustrate dipole location alterations in detail: 1) the anterior cingulate, 2) the primary somatosensory cortex, and 3) the premotor cortex. Previous studies have shown that these three areas are active in locomotion and error monitoring [8,9].…”