Objectives: this study was designed to investigate the coordination of jaw and tongue movements and the effects of physical characteristics of foods on the coordination of masticatory and extrinsic tongue muscle activities during mastication in freely behaving rabbits.
Methods: the phase duration and gape and excursion sizes of jaw movement as well as the area, duration and peak value of electromyographic burst activity in four muscles (jaw-closer and -opener and tongue-protrusive and -retrusive) were compared among four foods (rice, chow pellet, bread and banana). They were also compared between working and non-working sides.
Results: muscles recorded could be divided into two groups depending on their activity patterns during chewing; one muscle group consists of jaw-closer and tongue-retrusive muscles, which were active mainly in the jaw-closing phase, and the other group consists of jaw-opener, tongue-protrusive and suprahyoid muscles, which were active mainly in the jaw-opening phase. Those muscle activities were well coordinated during chewing and swallowing although the jaw movement pattern as well as the muscle activity pattern varied among the foods tested. In particular tongue and suprahyoid muscles appeared to have a critical role of squeezing the bolus between the tongue and palate in soft food chewing such as bread and banana on the working side.
Conclusions: sensory feedback could control the form of cyclical tongue and jaw movements to subserve the coordination in mastication.