The gag reflex is elicited by touching the posterior pharyngeal wall, tonsillar area, or the base of the tongue, with the tip of a thin wooden ("orange") stick. Depressing the tongue with a wooden spatula, and the use of a torch for illumination of the posterior pharynx, may be required to get a good view. There is a palatal response (palatal reflex), consisting of upward movement of the soft palate with ipsilateral deviation of the uvula; and a pharyngeal response (pharyngeal reflex or gag reflex) consisting of visible contraction of the pharyngeal wall. Lesser responses include medial movement, tensing, or corrugation of the pharyngeal wall. In addition there may be head withdrawal, eye watering, coughing, and retching. Hence there is variability of response in different individuals. Some studies claim the reflex is absent in many normal individuals, especially with increasing age, without evident functional impairment; whereas others find it in all healthy individuals, although variable stimulus intensity is required to elicit it.
The afferent limb of the reflex arc is the glossopharyngeal (IX) nerve, the efferent limb in the glossopharyngeal and vagus (X) nerves. Hence individual or combined lesions of the glossopharyngeal and vagus nerves depress the gag reflex, as in neurogenic bulbar palsy.
Dysphagia is common after a stroke, and the gag reflex is often performed to assess the integrity of swallowing. Some argue that absence of the reflex does not predict aspiration and is of little diagnostic value, since this may be a normal finding in elderly individuals, whereas pharyngeal sensation (feeling the stimulus at the back of the pharynx) is rarely absent in normals and is a better predictor of the absence of aspiration. Others find that even a brisk pharyngeal response in motor neurone disease may be associated with impaired swallowing. Hence the value of the gag reflex remains debatable. A video swallow may be a better technique to assess the integrity of swallowing.
Davies AE, Kidd D, Stone SP, MacMahon J. Pharyngeal sensation and gag reflex in healthy subjects. Lancet 1995; 345: 487-488
Hughes TAT, Wiles CM. Palatal and pharyngeal reflexes in health and motor neuron disease. Journal of Neurology, Neurosurgery andPsychiatry 1996; 61: 96-98