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mise à jour du
31 juillet 2003
 Arch Neurol
1982; 39; 435-436
Stimulus evoked oral automatisms
in the Locked-in syndrome
G. Bauer, M. Prugger, E. Rumpl
Universitätsklinik für Neurologie AnichstraBe 35, A-6020 Innsbruck, Austria
Involuntary motor phenomena in the locked-in syndrome


The locked-in syndrome (LIS) denotes quadriplegia owing to bilateral transsection of pyramidal tracts at the level of pons or cerebral peduncles. In a previous article, several voluntary motor phenomena occurring in LIS were described. Oral motor patterns were not observed in these cases and to our knowledge have been mentioned only once in the literature. This was in contrast to observations in cerebral malformations and in severe posttraumatic brain damage. Since our interest was attracted to this contradiction, we were able to observe three patients with LIS in whom oral automatisms occurred secondary to local (oral and perioral) and general stimulation.


Case 1. A 59-year-old woman had been hypertensive for ten years. She had experienced two episodes of transient neurological deficits followed by complete recovery. She was admitted because of sudden left-sided weakness and slurred speech. Neurological deficits indicated extensive brainstein involvernent. The speech was dysarthric, both eyes were deviated to the left, and nystagmus was observed in a vertical plane. Quadriparesis was accentuated in the right extremities. Plantar responses were extensor. Secondary to noxious stimulation extensor posturing occurred on the right side and flexor posturing on the left.

The next day, neurological symptoms had deteriorated. Except for vertical eye movements, the patient was completely paralyzed, including facial movements. She was alert, and by blinking, a communication code could be established. Seven days after admission, the patient remained in a nearly classic locked-in condition. At this time several involuntary motor phenomena could be observed. Bilateral extensor posturing and a grimacing pain reaction occurred after noxious stimulation. Sighing and groaning were noted but were not linked to any exogenous stimulus. With oral and perioral stimulation, sucking and chewing could be elicited. These movements showed a stereotyped sequence and could be regularly triggered, although diminution of response was evident with repeated stimulation. The response could also be elicited with noxious stimuli applied at the shoulder fold, but the response was less constant.

The EEC was minimally abnormal with sporadic theta waves over both temporal regions. The 8- to 10-eps alpha rhythm was blocked by eye opening. A computed tomographie (CT) scan was normal. Cerebral angiography disclosed severe sclerotic abnormalities of both carotid arteries and a complete occlusion of the basilar artery.

Case 2. A 51-year-old woman suffered from severe headache three days before admission. She was admitted in stupor with small pupils, skewed deviation of the eyes, extensor rigidity of all four extremities, and upgoing toes bilaterally. Aroused, she opened her eyes and moved them in a vertical plane. Five days later the condition had deteriorated. Except for vertical eye movements and weak movements of the left hand, she was completely paralyzed. Ocular bobbing was noted. Although some elouding of consciousness was evident, communication by eye blinking was possible. The patient denied disturbance of tactile and painful sensibility in the face, but left-sided hemihypaesthesia was signaled below the trigeminal level.

Oral and perioral stimulation produced chewing automatisms. Stimulation of other parts of the body were not effective. Oral movements never occurred spontaneously.

The EEG was moderately abnormal with intermittent 3- to 5-eps activity over both temporal regions. An 8- to 10-eps alpha rhythm was present and blocked by eye opening. A CT scan demonstrated a small hypodense area within the pons extending upward into the midbrain, more to the left. The clinical diagnosis was "incomplete LIS due to an infarct within the pons." Her condition was unchanged 20 days after admission.

Case 3. A 79-year-old housewife was in good condition until one month before admission, when attacks of dizziness accompanied by raised BP occurred. She was admitted because of rapidly developing right-sided hemiparesis and slurred speech. The next day she was immobile except for vertical gaze movements. She was able to use these movements for communication. Ten days later, her neurological condition has slightly improved. Inconspicuous opening of the mouth was possible. In contrast to the small extent of voluntary movements, automatic sighing and facial expression of pain occurred secondary to noxious stimulation. Prolonged chewing was observed after perioral stimulation.

The EEG was slightly abnormal, with a 6- to 7-eps basic rhythm that was blocked by eye opening. Some diffuse 2- to 3-eps activity was interspersed. Spinal fluid and CT sean were normal.

A clinical diagnosis of "classical LIS due to a pontine infarct" was made. The patient died 18 days after admission. Autopsy results disclosed atherosclerosis of the basilar and both vertebral arteries. An infarct 1 cm in diameter was found within the ventral pons.


As shown by observations in complex partial epileptic seizures and by stimulation experiments in man, the central representation of oral automatisms are located bilaterally in the most caudal part of the precentral gyrus and near the amygdaloid nucleus. Oral automatisms consist of sucking, chewing, and swallowing and may occur reflexlike without participation of more central structures.

From animal experiments and clinical observations a primordial system of coordination for mastication can be assumed in the medulla oblongata, including the motor nuclei of the fifth, seventh, and twelfth cranial nerves. Oral automatisms are most easily elicited by stimulation of the mucous membrane of the lips, tongue, and palate. In newborns, sucking can also be elicited by widespread tactile and acoustic stimuli.

Observations in malformed humans confirm the existence of a bulbar system for mastication. The pattern of oral automatisms changes with aging. Sucking appears first and is replaced by chewing. Eventually, all oral movements are voluntarily controlled. Stimulus-sensitive oral automatisms occur in normal newborns but cannot be seen in adults except under pathologic conditions.

The LIS seems to be another pathologic condition leading to involuntary stimulus evoked oral automatisms. As in newborns the oral and perioral region is the most sensitive region but other regions are also susceptible. Regarding the ventral part of the pons as the most common localization of lesions leading to an LIS, one cannot rule out extrapyramidal mechanisms. However, according to the observations in malformations, the most probable explanation for oral motor phenomena in LIS is the loss of pyramidal control over the bulbar system for mastication.

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