[Sleep disorders from the neurological viewpoint].
Sleep can be measured by EEG or a monitor which records motor activity. In this way objective data on sleep behavior can be obtained from patients. Total sleep time over 24 hours remains remarkably constant above age 20. Therefore, any changes in total sleep time can be considered to be pathologic. A true shortening of sleep time is rare and is usually associated with a psychosis. More often "common sleep disorders" are encountered, which show a normal total sleep time per 24 hours. Prolonged sleep, usually associated with increased day-time somnolence, is often caused by chronic meningitis or intracranial space occupying lesions. Narcolepsy is a separate entity which has no connection with epilepsy, in which the different physiological components of sleep are desynchronized.