RT Book, Section A1 Brust, John C. M. SR Print(0) ID 1180669405 T1 Examination of the Comatose Patient T2 Practice of Neural Science: A Case-Based Approach YR 1 FD 1 PB PP New York, NY SN 9781264258956 LK neurology.mhmedical.com/content.aspx?aid=1180669405 RD 2024/10/14 AB Consciousness is awareness of oneself and one’s environment; it requires both arousal and mental content. The anatomic substrate for arousal is the reticular activating system of the brain stem and thalamus; the anatomic substrate for mental content is the cerebrum. Impaired consciousness thus follows either small brain stem lesions or large bilateral cerebral lesions. Temporary loss of consciousness can follow sudden severe lesions within a single cerebral hemisphere, for example, intracerebral hemorrhage. The mechanism is a poorly understood transsynaptic functional suppression of the opposite hemisphere referred to as diaschisis and reflected in decreased blood flow, oxygen uptake, and glucose metabolism. Prolonged or permanent loss of consciousness, however, indicates damage—structural or metabolic—either to the cerebral hemispheres bilaterally or to the reticular activating system.