Johanna Wagner | Keeping in step: Entrainment of low-gamma activity in the brain with gait rhythm

Cortical processes occurring during upright human gait are not yet well studied. Source-resolved analysis of high-density electroencephalographic (EEG) data is a promising approach to monitoring brain activities supporting walking. In two recent studies, we investigated spectral patterns of high-density EEG data from able-bodied volunteers in a robot-assisted gait-training experiment. Using independent component analysis (ICA), we were able to show that lower gamma band modulations (24-40 Hz) in premotor cortex are timed to the gait cycle (Wagner et al., 2012; Wagner et al., 2014). It has been previously shown that oscillations in auditory and motor cortices may entrain to external rhythms, and this mechanism has been connected to the encoding of temporal information. Predictive timing is essential when performing rhythmic movements. I will present results from a third study in which I examined the EEG of participants attempting to step in time to an auditory pacing tone sequence. Subjects had to adapt their step length and rate to shifts in tempo of the pacing stimulus (i.e., following unforeseen shifts to a faster or slower tempo). The analysis revealed differential involvement of various cortical rhythms during steady state walking versus during adaptation to pacing tempo shifts. The results suggest that entrainment of low gamma activity to gait rhythm may directly reflect step timekeeping.