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mise à jour du
11 novembre 2002
 Bulletin of the Menninger Clinic
A homeostatic reflex and
its psychological significance
Heinz E. Lehmann
Professor of Psychiatry, McGill University, Montreal, Quebec, Canada
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Yawning is a common phenomenon that is an expression of certain physiological and psychological states, yet it bas received remarkably little attention in the medical literature. Dumpert (1921), Hauptmann (1920), and Lewy (1921) reached some conclusions regarding the nature of yawning in connection with observations of patients with encephalitis lethargica; however, after the 1920s the subject was again disregarded. On the basis of certain clinical and experimental observations which may have some psychiatric significance and which, to my knowledge, have not yet been described, a review of the matter of yawning appeared justified. [...]
Clinical Observations : It is an old clinical observation (Russell 1891; Geigel 1908) that persons suffering from an acute physical illness never yawn as long as their condition is serious. Nurses have learned to recognize the return of yawning as a sign of patients' convalescence, particularly in those patients who have infectious diseases. The literature, however, reports few observations regarding yawning in psychotic patients, although Hauptmann (1920) made mention of its possible significance.

Some time ago I was struck by the conspicuous scarcity of yawning among mental patients. I informally recorded the incidence of people yawning in public gatherings, on buses, in restaurants, at scientific meetings, and on mental hospital wards. These observations confirmed my impression that yawning among the mentally ill is unusually rare. There were two exceptions: patients receiving large doses of sedatives and those diagnosed as suffering from organic brain syndrome. Of course, the absence of yawning in patients with psychoses associated with constant psychomotor excitement or increased nervous tension was not surprising since excitement or emotional tension usually excludes the occurrence of yawning in normal individuals. However, the majority of patients I observed were quiet, inactive, indifferent persons suffering from schizophrenia. Their failure to yawn requires an explanation.

One of the most consistent physiological findings about patients with schizophrenia is defective homeostasis. The schizophrenic patient's ability to adjust to changes in the internal milieu is impaired. Slight reductions of the schizophrenic subject's brain metabolism would, therefore, provoke a homeostatic response less easily than in a normal person. Yawning might not be elicited unless the yawning provoking stimulus assumes an unusual strength such as that provided by hypoglycemia or by barbiturates.

As I have mentioned, the principal psychological agent to produce yawning-boredom-is an affect characterized by an extraverted attitude, a searching tendency toward reality. The schizophrenic subject's typical withdrawal from reality and his affective blunting make it almost impossible for him to be truly bored; his passivity, indifference, and daydreaming must not be confused with boredom. In addition, the schizophrenic individual can hardly be expected to imitate unconsciously the yawning of another person since he is not likely to transfer sufficient interest to other persons in his surroundings. Therefore, when a schizophrenic patient yawns as a result of boredom or unconmous imitation, it shows that the patient's contact with reality is not entirely lost and that he is making an effort to maintain it. In fact, when any psychiatric patient yawns, it is a signal that he is in an accessible mood, regardless of his general mental state or diagnosis.

Of course, yawning is by no means completely absent in schizophrenic patients. Its incidence, however, appears to be much lower in schizophrenia than in normal mental conditions or in other mental diseases. The occurrence of yawning in early schizophrenia may be evaluated as a favorable sign; however, it seems to be of ominous significance in chronic schizophrenia. One may theorize that yawning in the acute schizophrenic patient is the reflection of a fairly intact homeostatic system and possibly the expression of the patient's efforts to retain his contact with reality. In the chronic stages of the disease, yawning may be indicative of structural brain changes and the formation of a new, permanent, and pathological relationship to the outside world, characterized by complacency and the complete loss of the inner stress and tension that should accompany even partial insight.

Experimental Induction of Yawning : Yawning is an elusive phenomenon and lends itself poorly to experimental investigation. It is usually difficult, if not impossible, to determine which psychic or somatic cause or combination of causes is actually responsible for spontaneous yawning.

In an attempt to elicit yawning under fairly uniform and observable conditions, 180 mental patients were administered a standardized cerebral depressant that would bring into action the homeostatic function of yawning. Psychological factors, such as an intention to remain awake and in contact with the environment, could have been present but were certainly in the background as yawning-producing agents in these cases. The subjects selected to participate in the experiment were divided into three groups of sixty patients each. Group I consisted of only those patients who, beyond any doubt, had been recognized by several staff members as schizophrenic and who presented no atypical features. Group II included only those patients suffering from a variety of psychoses caused by and associated with neurological brain lesions. Group III was made up of persons with miscellaneous functional mental disorders that did not belong in either the schizophrenic or in the "organic" group.

These 180 patients were intravenously administered a 3 percent solution of pentobarbital, a barbiturate, usually at a rate of not more than 1 cc per 30 seconds. The investigator carried on a running conversation with the patient during the injection, telling him that the injection would not hurt or incommodate him in uny way but would make him feel sleepy. When yawning occurred, the reaction was counted as positive and the injection was discontinued, unless a more profound narcosis was desired for reasons other than the experiment. When no yawning occurred after a maximum of 0.3 g of pentobarbital (10 cc of the 3 percent solution) had been administered, the injection was terminated and the reaction was counted as negative.

In some cases, yawning occurred frequently after about 0.15 g of pentobarbital had been injected. At the same time, the patient's speech became slurred and he stated that he felt dizzy, lightheaded, or drowsy. His respiration then became shallow and infrequent; yawning occurred frequently at this stage, too. As a rule, respiration became regular again within a minute or two, and the patient then slept for several hours if left undisturbed. In other cases, yawning was delayed and appeared after the patient had passed from the somnolent stage into profound sleep. Therefore, a reaction was counted as negative only when yawning was not observed during the injection or within 90 seconds following it. Patients who did not yawn often sighed deeply when they began to feel drowsy; however, yawning was defined as an inspiration accompanied by tonic contraction of the facial muscles and by opening of the mouth.

The difference in the incidence of induced yawning in schizophrenic subjects as compared with those suffering from a psychosis with structural brain changes is evident and of statistical significance (X2 = 26.38; df = 2; p < 0.001): 26.7 percent positive responses in schizophrenic patients against 71.7 percent positive responses in patients with organic brain syndrome. The positive responses for the miscellaneous group hold a middle position. As with spontaneous yawning, induced yawning was less likely to occur in tense, excited, or acutely ill individuals than in quiet, cooperative patients. Very resistive or excited patients showed little response to the pentobarbital injection. Other patients who expressed marked euphoria or depression usually did not yawn. A general rule seems to be that, ceteris paribus 1 yawning is favored by the absence of psychomotor excitement, emotional tension, and acute, active illness. Thus a depressed patient in a depressive stupor or a patient in a manic delirium would probably fail to show this response.

Within Group III, a distinct majority of psychoneurotic patients showed negative yawning reactions. The psychoneurotic individual behaves like the schizophrenic patient in responding to the sudden reduction of cerebral function, especially when anxiety and obsessive symptoms are prominent. Among those with affective psychoses, lhe: were more negative responses in the manic-depressive group an positive responses in the involutional melancholia group.

Aside from the quantitative differences among the three groups, there were also qualitative differences. If yawning occurred in schizophrenic patients, it usually appeared in a peculiar, short, superficial manner and was not repeated, while the yawning of a patient with structural brain lesion tended to be frequent, deep, and prolonged. One patient, suffering from involutional melancholia without evident cerebral lesion, yawned so forcefully after awakening from the pentobarbital narcosis that he dislocated his jaw and required manual reduction. As with spontaneous yawning, the induced yawning occurring in early schizophrenia seemed to have favorable significance, whereas in chronic cases it seemed to be evidence of marked deterioration.

In one particular case, the yawning response to the pentobarbital injection gave a diagnostic hint. A Chinese man was admitted to the hospital because of peculiar behavior and general inertia. Language difficulties prevented the taking of an adequate history frorn the relatives and made the psychiatric examination of the patient difficult. The physical examination yielded no definite results, and a provisional diagnosis of simple schizophrenia was made. However, the patient showed such a frequent and intensive yawning response to pentobarbital that the staff doubted that they were dealing with a schizophrenic individual. The spinal fluid findings then revealed that the patient was suffering from general paresis.


(1) Yawning is a phylogenetically and ontogenetically old reflex that occurs under somatic conditions which seem to be characterized by a reduction of brain metabolism.

(2) There is reasonable support for the view that yawning originated as a self-adjusting mechanism of the organism, a homeostatic reflex which operates through the tonic contraction of large muscle groups and temporarily improves circulation in general and blood flow to the brain in particular.

(3) The principal psychological reasons for yawning are boredom and unconscious imitation.

(4) Boredom is an affect characterized by an extraverted attitude.

(5) Unconscious imitation requires transferring interest to something in the outside world.

(6) Yawning is a signal that the person is making an effort to maintain contact with the outside world.

(7) Psychotic persons yawn rarely, except when suffering from organic brain syndrome.

(8) Spontaneous yawning in a psychotic, particularly a schizophrenic, individual may be a signal that he is in an accessible mood.

(9) When yawning is induced experimentally by pharmacosedation, the responses of schizophrenic subjects differ significantly from those of psychotic subjects with structural brain lesions.

(10) In persons with psychiatric conditions, yawning may assume the value of a clinical symptom with diagnostic and prognostic implications.


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