Abstract
Tongue is unique and each half of the tongue is represented bilaterally in brain and is being used as an effective interface to send signals to central nervous system. Tongue movements and tongue stimulation have been used in various types of rehabilitation. The purpose of this study is to review all articles related to tongue stimulation. All studies including reviews, case, cohort and experimental studies, which dealt with tongue stimulation, periglossal stimulation, or hypoglossal stimulation during the period between 1981 to 2020 were screened and a total of 41 studies comprising of 9 review articles, 30 experimental studies and 2 case reports were included for review. The methodology quality of the experimental studies has been analyzed using PEDro score and level of evidence measure. Electrical stimulation of the tongue was performed on normal subjects to find out the taste sensation and its similarity with other liquids. Hypoglossal stimulation has been found to stimulate the muscles of the tongue and it stiffens the posterior aspect of tongue and walls of the pharynx, thereby reducing the symptoms in obstructive sleep apnea. Stimulation of the muscles of the tongue also improves swallowing functions in dysphagia patients. Tongue stimulation, using a variety of devices and in combination with balance exercises, has also been used to improve balance in stroke, multiple sclerosis and spinal cord injury patients by inducing activity in cerebellum and brainstem, which process the balance networks. Tongue movements and tongue stimulation along with upper limb rehabilitation, have also been used in improving upper limb functions in stroke patients based on the principles of Hebbian theory. Thus, tongue stimulation along with targeted exercise program becomes a novel mode of therapy in inducing neuroplasticity and can be used in wide variety of patients in rehabilitation. This review will input to the clinicians and researcher for conducting further research on tongue stimulation. Further long-term follow-up studies can also be done to find out the neuroplastic changes in brain following tongue stimulation.
Highlights
We found that several studies have been done on tongue stimulation in various subjects – normal as well as on disease conditions
The studies were done on normal subjects, balance impaired patients, multiple sclerosis, spinal cord injury and stroke patients to find out the effect of tongue stimulation on taste quality, pharyngeal cross-sectional area, balance and motor recovery (Table 2 and Table 3)
Most subjects were able to perceive and discriminate electrotactile stimulation better on one side of the tongue, and perception was affected by the orientation of stimulating electrodes
Summary
The tongue is unique and has bilateral representation in the brain homunculus. The behavioral and voluntary tongue movements is controlled by corticobulbar connections which mediate between motor cortex and lower motor neurons. The cell bodies of these neurons are located bilaterally in the hypoglossal nuclei on the dorsal surface of the medulla [1]. The tongue, a muscular organ, plays a vital role in various body functions such as breathing, speaking, chewing and swallowing (Figure 1) [2, 26]. According to one line of thought, the tongue has paracrine/autocrine mechanism of action to produce different substances which interact with the whole body. Connections with the tongue should be considered to enhance patient rehabilitation programs to get better therapeutic results [2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
