IADR Abstract Archives
Masticatory and Brux-like Motor Patterns in the Freely Behaving Rat:Electromyography and Sonomicrometry
Objectives: Human bruxism involves the involuntary grinding or gnashing of the teeth. Untreated, bruxism may lead to a loss of enamel, broken fillings, headaches, and a number of temporomandibular disorders. The etiology of bruxism is not fully understood, nor is the underlying neural-substrates. So far, we know that the nervous system produces precise motor patterns by utilizing special circuits known as central pattern generators (CPGs) located in the central nervous system. The general principle is that multifunctional interneurons that comprise a CPG may form a core, multipurpose circuit that generates elements of coordinated motor output utilized for several types of motor patterns. Our main objective is to characterize and compare different motor pattern forms that are produced by the CPG that controls oral facial movements.
Methods: We conducted electromyogram (EMG) recordings of a jaw closing muscle (anterior superficial masseter) and a jaw opening muscle (anterior digastric) using a laboratory rat as an animal model (n=11 animals, 290 cycles each). Sonomicrometry, a technology that uses ultrasound to determine distance, was also utilized to compare the physical movement of the anterior superficial masseter muscle with its respective EMG firing pattern.
Results: We found that the digastric and superficial masseter muscles were in antiphase during mastication (mean = 0.76), and were in phase during bruxing/thegosis (mean = 0.11). We also calculated a vector length value that indicates the strength of coupling (r) of the selected muscles on a scale from 0 to 1. The strength of coupling during brux-like movements (r = 0.80) were also strongly coupled during the reduction phase of mastication (r = 0.85).
Conclusions: Our preliminary sonomicrometry and EMG measurements of the anterior superficial masseter muscle indicate that it might exhibit greater influence over jaw movement during brux-like motor patterns than it does during masticatory patterns. These results suggests that the neuromuscular properties of the superficial massester muscle might prove vital for understanding the underlying neurological substrates of human bruxism.
Methods: We conducted electromyogram (EMG) recordings of a jaw closing muscle (anterior superficial masseter) and a jaw opening muscle (anterior digastric) using a laboratory rat as an animal model (n=11 animals, 290 cycles each). Sonomicrometry, a technology that uses ultrasound to determine distance, was also utilized to compare the physical movement of the anterior superficial masseter muscle with its respective EMG firing pattern.
Results: We found that the digastric and superficial masseter muscles were in antiphase during mastication (mean = 0.76), and were in phase during bruxing/thegosis (mean = 0.11). We also calculated a vector length value that indicates the strength of coupling (r) of the selected muscles on a scale from 0 to 1. The strength of coupling during brux-like movements (r = 0.80) were also strongly coupled during the reduction phase of mastication (r = 0.85).
Conclusions: Our preliminary sonomicrometry and EMG measurements of the anterior superficial masseter muscle indicate that it might exhibit greater influence over jaw movement during brux-like motor patterns than it does during masticatory patterns. These results suggests that the neuromuscular properties of the superficial massester muscle might prove vital for understanding the underlying neurological substrates of human bruxism.