Cortico-muscular communication for motor control of the tongue in humans: A review

Abstract

BackgroundSophisticated voluntary movements of the tongue are essential to speech articulation and swallowing in humans. Voluntary tongue movements are finely controlled by communications between the cortex and tongue muscles. A large number of previous studies have reported that functional connections between the cortex and muscles are reflected by cortico-muscular coherence (CMC), which is measured between electroencephalography (EEG) or magnetoencephalography (MEG) and surface electromyography (EMG), during isometric finger movements in humans. Recent studies indicate that CMC reflects a bi-directional flow of information between the cortex and fingers, along the descending corticospinal pathway and with ascending sensory feedback. However, CMC for the tongue has not been well-studied, despite the fact that increased knowledge would be helpful in understanding cortical entrainment of voluntary tongue movements. HighlightCMC was recently demonstrated using whole-head MEG signals and EMG signals from both sides of the tongue. CMC was reflected over both hemispheres, for each side of the tongue, and at two frequency bands during isometric tongue protrusions: the β band at 15–35Hz and a low-frequency band at 2–10Hz. ConclusionThis review provides a detailed description of the functional connection between the bilateral cortex and each side of the tongue during sustained tongue movements in humans, using CMC analyses.