Disorders of Consciousness

The concept of consciousness has fascinated philosophers, psychologists and neurophysiologists for a long time; however, it remains difficult to give its univocal and universally accepted definition. Consciousness is defined as “the state of full awareness of the self and one’s relationship to the environment”; consequently, a distinction must be made between consciousness (or awareness) and vigilance/alertness (wakefulness). In fact, it is possible for a patient to be conscious, but unresponsive to the examiner, for lack of sensory inputs or for psychiatric reasons. Conversely, a subject can be alert and awake with open eyes, but not conscious and not aware (in part or at all) of itself and of the environment. From a neurophysiological point of view, it has been demonstrated that the brainstem Reticular Activating System (RAS) is responsible for the state of alertness, through its projections to the thalamus and cortex. The integrity of the upper cortical centres, which are closely related to each other and receive the reticular activating stimuli, is also essential for the maintenance of consciousness level. Therefore, Disorders Of Consciousness (DOC) and vigilance may depend on damage to one or both of these neurofunctional systems, acute or chronic, reversible or irreversible. Serious damage to the reticular system, with or without concomitant widespread cortical damage, can produce a state of coma. Coma is then a pathological condition in which the subject lies with eyes closed and he is neither conscious nor alert, with altered - or completely absent - responsiveness to stimuli. In case of widespread damage to the cerebral cortex without involvement of the RAS, a particular condition - named Vegetative State (VS) - may occur: the consciousness of self and of the environment is impaired, but a certain level of vigilance is still preserved. Moreover, there also exist several neurological conditions that can be defined as “borderline”, such as the Minimally Conscious State. Finally, brain death is the irreversible definitive impairment of both the cortical and brainstem functions. Electroencephalography is an important diagnostic and prognostic tool, useful to better characterise the evolution of a coma state, to recognise any kind of epileptiform activity - that could be clinically hidden - and to monitor the effects of antiepileptic drugs, level of sedation, and treatment of intracranial hypertension.