Cortical Mechanisms of Tongue Sensorimotor Functions in Humans: A Review of the Magnetoencephalography Approach

Abstract

The tongue plays important roles in a variety of critical human oral functions, including speech production, swallowing, mastication and respiration. These sophisticated tongue movements are in part finely regulated by cortical entrainment. Many studies have examined sensorimotor processing in the limbs using magnetoencephalography (MEG), which has high spatiotemporal resolution. Such studies have employed multiple methods of analysis, including somatosensory evoked fields (SEFs), movement-related cortical fields (MRCFs), event-related desynchronization/synchronization (ERD/ERS) associated with somatosensory stimulation or movement and cortico-muscular coherence (CMC) during sustained movement. However, the cortical mechanisms underlying the sensorimotor functions of the tongue remain unclear, as contamination artifacts induced by stimulation and/or muscle activity within the orofacial region complicates MEG analysis in the oral region. Recently, several studies have obtained MEG recordings from the tongue region using improved stimulation methods and movement tasks. In the present review, we provide a detailed overview of tongue sensorimotor processing in humans, based on the findings of recent MEG studies. In addition, we review the clinical applications of MEG for sensory disturbances of the tongue caused by damage to the lingual nerve. Increased knowledge of the physiological and pathophysiological mechanisms underlying tongue sensorimotor processing may improve our understanding of the cortical entrainment of human oral functions.

Event-Related Desynchronization and Corticomuscular Coherence Observed During Volitional Swallow by Electroencephalography Recordings in Humans

“…We have found that the significant CMC existed in all nine channels covering the lateral and medial parts of the sensorimotor area in theta, alpha, and beta frequency bands in accordance with the previous works (Maezawa et al, 2014(Maezawa et al, , 2016Maezawa, 2017). For the finger muscles, CMC was not consistently observed in the theta and alpha frequency bands (Mima and Hallett, 1999).…”

“…Transcranial magnetic stimulation (TMS) works showed changes in corticomotoneuronal activities by the evaluation of motor-evoked potentials in the pharyngeal muscles in the resting state after repetitive TMS, which increased the cortical excitability of the stimulated area (Michou et al, 2014). In the previous works using MEG, significant CMCs in theta, alpha, and beta frequency bands have been found during tongue protrusion task, which suggests that cortical motor commands can be evaluated in oral apparatus by CMC (Maezawa et al, 2014(Maezawa et al, , 2016Maezawa, 2017). Although it is important to evaluate the corticomotoneuronal activities during swallow movements with activated submental group muscles and pharyngeal muscles (Ding et al, 2002), there has been no analogous work on them.…”

“…If ERD and CMC can be detected by EEG recordings using a similar way with the previous MEG studies, it would be easily applicable in clinical practice for the evaluation of swallow dysfunction in neurological patients. Therefore, we investigated them based on the hypothesis that ERDs and CMCs could be measured in the bilateral sensorimotor, premotor, and prefrontal areas as reported by the previous MEG works (Dziewas et al, 2003;Suntrup et al, 2013Suntrup et al, , 2014Suntrup et al, , 2015Maezawa et al, 2014Maezawa et al, , 2016Maezawa, 2017). The submental group muscle activity was used to differentiate the swallow activation from the baseline according to the previous MEG works (Dziewas et al, 2003;Suntrup et al, 2013Suntrup et al, , 2014Suntrup et al, , 2015 because the onset of the activity was close to the start of the pharyngeal phase (Ding et al, 2002).…”

Effect of Electrical Stimulation of Tongue in Rehabilitation – A Systematic Review

“…Alexander B. Remsik et al [40] did a randomized controlled trial on 21 cerebrovascular accident patients with persistent upper extremity impairment. They received a maximum of 18-30 hours of therapeutic interventions with novel electroencephalogram-based brain computer interface driven functional electrical stimulation device (EEG -BCI -FES).…”

Functional cortical localization of the tongue using corticokinematic coherence with a deep learning-assisted motion capture system

“…Conventional CKC methods quantify the coupling between magnetoencephalographic (MEG) signals and finger kinematics, which are measured using an accelerometer (ACC) during repetitive, rhythmic, and voluntary finger movements (Bourguignon et al, 2011;. Previous studies have shown that the CKC mainly reflects the proprioceptive input into the SM1 (Piitulainen et al, 2013a;Bourguignon et al, 2015;2017); this feature is comparable to the strongest deflections observed in the cortical movement evoked fields (MEFs) associated with voluntary finger movements (Cheyne et al, 1989;Gerloff et al, 1998). However, it is difficult to apply this technique to regions of the tongue using an ACC because the ACC produces excessive magnetic artifacts, which easily contaminate the cortical magnetic activity due to the short distance between the tongue and MEG sensors.…”