Introduction

Coma is classically defined as loss of motility, sensation and consciousness with preservation of autonomic functions. Though not inaccurate, this definition is no longer considered as adequate. If loss of consciousness seems to be a necessary and sutficient symptom to talk of coma (it being understood that we are dealing with a lethargic state very different from sleep, in as much as the subject cannot be roused by strong external stimulation), it follows that loss of voluntary motility and sensation are natural consequences of the loss of consciousness and add no useful precision to the definition. On the other hand, autonomic disturbances almost invariably accompany a comatose state; this at least was the case prior to the introduction of modern resus citation methods. For these reasons, the definition of coma rests on the definition of consciousness. But as Jackson himself has stressed, consciousness is very difficult to define. We refer the reader to the following recent papers concerning the problem of definition of consciousness in neurophysiological terms (Fessard 1954; Alajouanine 1957; Walshe 1957; Eccles 1966; Adrian 1966; MacKay 1966). However, modern methods of investigation and in particular neurophysiological clinical methods applied to the study of prolonged comas (the symptomatology of which is less variable than that of acute comas) and the importance attached to the dynamic and dialectic concept of perceptivity * and of reactivity *, will lead to another definition borrowed from psychophysiology. According to this definition, consciousness is that central nervous process which gives significance to a stimulus from the external environment. We can thus understand by consciousness that function of the nervous system which is concerned with the perceptual experience of information from the environment and from our own body (Alajouanine 1957). The multiple disintegration of consciousness observed in coma can therefore be defined as the absence, in the patient, of objective clinical (or paraclinical) signs of appreciation of his environment. It is this behavioural deficiency that the clinician explores by simple means: failure to rouse a comatose patient by calling his name or applying a painful stimulus.

* The terms 'perceptivity' (perceptivité) and 'reactivity' (réactivité) are adjectives applied to central mechanisms which are necessary for perception and reaction.

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