Brain-muscle connectivity during gait: corticomuscular coherence as quantification of the cognitive reserve

A detailed comprehension of the central and peripheral processes underlying walking is essential to develop effective therapeutic interventions to slow down gait decline with age, and rehabilitation strategies to maximize motor recovery for patients with damages at the central nervous system. The combined use of electromyography (EMG) and electroencephalography (EEG), in the framework of coherence analysis, has recently established for neuromotor integrity/impairment assessment. In this study, we propose corticomuscular (EEG-EMG) and inter/intramuscular (EMG-EMG) coherences as measures of the cognitive reserve, i.e., the process whereby a wider repertoire of cognitive strategies, as well as more flexible and efficient strategies, can moderate the manifestation of brain disease/damage. We recorded EEG signals from the main brain source locations and superficial EMG signals from the main leg muscles involved in gait in 16 healthy young adults (age [≤]30 years) and 13 healthy elderly (age [≥]65 years) during three different overground walking conditions (i.e., spontaneous walking, walking with cognitive dual-task, and walking with targets drawn on the floor). In all conditions, we calculated corticomuscular and inter/intramuscular coherences. We observed higher corticomuscular and inter/intramuscular coherences during targeted walking compared to spontaneous walking in both groups, even if the increase was greater in young people. Considering dual-task walking compared to spontaneous walking, only corticomuscular coherence in the elderly increased. These results suggest age-related differences in cognitive reserve that reflect different abilities to perform complex cognitive or motor tasks during gait. This study demonstrates the feasibility, repeatability, and effectiveness of the proposed method to investigate brain-to-muscle connectivity during different gait conditions, to study the related changes with age, and to quantify the cognitive reserve.