Consciousness

Consciousness consists of two principal components, alertness and awareness. Alertness, or wakefulness, including electroencephalographically documented arousal, is dependent on the ascending reticular activating system (ARAS), located in the tegmentum of the upper brainstem and diencephalon and projecting through the midline and intralaminar nuclei of the thalamus to the cerebral cortex ( Kinomura.et.a/ 1996) (Fig 1). Activation of the ARAS allows sensory information to be transmitted to the cerebral cortex for further processing (CD Figure 1). Awareness, or 'content', refers to higher functions including judgment, memory, emotions, and interpretation of sensory information. This depends on the integrated function of the cerebral cortex and the subcortical structures, particularly the thalamus.

Fig. 1 The ascending reticular system and its projections. This diagram depicts the brainstem, containing the reticular formation and the ascending sensory pathways (lemnisci), the thalamus, the caudate nucleus, and higher structures (limbic system, motor areas, and cerebral cortex). Projections to the hypothalamus are also shown.

Fig. 1 The ascending reticular system and its projections. This diagram depicts the brainstem, containing the reticular formation and the ascending sensory pathways (lemnisci), the thalamus, the caudate nucleus, and higher structures (limbic system, motor areas, and cerebral cortex). Projections to the hypothalamus are also shown.

Mesencephalic Reticular Formation

mesencephalic reticular formation, on the transfer of sensory information from the periphery to the cortex via the thalamic relay nuclei is emphasized.

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