Human jaw-opening muscle responses elicited by multiple-site electrical stimulation

Area of Science:

• Neuroscience
• Physiology
• Biomedical Engineering

Background:

• The human jaw-opening reflex is crucial for functions like chewing and speaking.
• Previous research suggests mechanical stimuli are needed to elicit this reflex.
• Understanding the neural pathways involved is key to addressing jaw dysfunction.

Purpose of the Study:

• To investigate the effects of electrical stimuli on human jaw muscle reflexes.
• To determine if electrical stimulation can elicit jaw-opening reflexes.
• To explore the conditions influencing these reflex responses.

Main Methods:

• Electrical stimuli were applied to the upper and lower gingiva around the right canines under various conditions (relaxation, active opening, clenching, wide-open).
• Reflex responses of suprahyoid and jaw-closing muscles were recorded using surface electrodes.
• Stimulation parameters, including intensity and location, were varied.

Main Results:

• Electrical stimulation elicited segmented reflex excitation in suprahyoid muscles and conventional excitation/inhibition in jaw-closing muscles when background activity was present.
• The suprahyoid muscle's excitatory reflex was stronger with simultaneous stimulation of multiple sites (upper and lower jaw) compared to single-site stimulation.
• Response latency increased with higher stimulus intensities, indicating a dose-dependent effect.

Conclusions:

• The human jaw-opening reflex can be elicited by electrical stimuli, supporting previous findings with mechanical stimuli.
• Maintaining background activity in jaw openers appears necessary for eliciting the reflex, possibly due to low-threshold afferent input.
• Spatial summation, achieved through multi-site stimulation, may enhance the reflex response.