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Yawning is a very common and phylogenetically ancient behavioural event that occurs in vertebrates under different conditions. A yawn consists of a stereotyped behavioural pattern that begins with an inspiration associated with marked dilatation of the pharynx. At the peak of inspiration there are associated facial movements and the final part of yawning is passive rapid expiration. During yawning a coordinated sequence of events takes place involving facial, oropharyngeal, tongue, and respiratory muscles, associated with activity in the axial extensor and limb extensor muscles and with autonomic changes characterised by an increased parasympathetic outflow. 1 The physiological stimuli that give rise to the yawning response and its functional significance are not clear. It has been shown that yawning frequency is not modified by hypercapnia or by pure oxygen breathing; it does not seem, therefore, to have a straightforward respiratory function. 2 Yawning occurs preferentially in conditions of low vigilance and causes transient increases in arousal as indicated by EEG desynchronisation, though an active role in the maintenance of arousal has not been demonstrated. The social importance of yawning is particularly evident in mammals, where it seems to have a communicative role in conditions of decreased vigilance. 2 The neural structures that control yawning are presumably located in the brain stem near to or within other respiratory and vasomotor centres, especially those that control facial mimicry, mastication, throat movements, respiration, and possibly stretching. 3 Excessive or pathological yawning is defined as a compulsive, repetitive action that is not triggered by appropriate stimuli such as fatigue or boredom. We describe here two cases of excessive yawning behaviour associated with ischaemic lesions in the brain stem.
CASE REPORTS
Patient 1
A 74 year old man was admitted to our clinic complaining of unsteadiness of stance and gait, lasting for 12 hours. The patient described an acute onset of excessive, repetitive, compulsive yawning that he was unable to control; the yawns were repeated at a frequency of about 3/minute. Forty minutes later the patient also noticed gait ataxia and inability to stand without assistance. When admitted to the hospital, neurological examination showed a slight intention tremor of the left arm and slight dysmetria in the finger-nose manoeuvre; no limb weakness was present and tendon reflexes were normal. The patient...