The notion of consciousness in the English scientific literature denotes a global ability to consciously perform elementary and intellectual tasks, to reason, plan, judge and retrieve information as well as the awareness of these functions belonging to the self, that is, being self-aware. consciousness can also be defined as continuous awareness of the external and internal environment, of the past and the present. The meaning of consciousness is different in various languages, but it invariably includes, the conscious person is capable to learn, retrieve and use information. Disturbance or loss of consciousness in the Hungarian medical language indicates decreased alertness or arousability rather than the impairment of the complex mental ability. Awareness denotes the spiritual process of perception and analysis of stimuli from the inner and external world. Alertness is a prerequisite of awareness. Clinical observations suggest that the lesions of specific structures of the brain may lead to specific malfunction of consciousness, therefore, consciousness must be the product of neural activity. "Higher functions" of human mental ability have been ascribed to the prefrontal and parietal association cortices. The paleocerebrum, limbic system and their connections have been considered to be the center of emotions, feelings, attention, motivation and autonomic functions. Recent evidence indicates that these phylogenetically ancient structures play an important role in the processes of acquiring, storing and retrieving information. The hippocampus has a key role in regulating memory, learning, emotion and motivation. Impaired consciousness in the neurological practice is classified based on tests for conscious behavior and by analyzing the following responses: 1. elementary reactions to sensory stimuli--these are impaired in hypnoid unconsciousness, 2. intellectual reactions to cognitive stimuli--these indicate the impairment of cognitive contents in non-hypnoid unconsciousness. Obviously, disturbance of elementary reactions related to alertness and disturbance of intellectual performance overlap. In conditions with reduced ability to react to or to perceive external stimuli the cognitive disturbance of consciousness cannot fully be explored.