ABSTRACT
Sleep alternates with waking in a regular manner, and sleep-waking is one of the most important and prominent biological rhythms. The chapter examines the behavioural, the physiological, and the electroencephalographic changes associated with sleep. Sleep is purposive in the Darwinian sense, because it has survival value and apparently fulfils a biological need. Physiological responses during sleep have been investigated extensively by N. Kleitman and other investigators. In humans and other diurnal species, the absence of auditory, visual, pain and other stimuli is conducive to sleep. Sleep-waking is one of the prominent circadian rhythms in the human adult and in many other species. Certain hormones influence the general excitability of the central nervous system, either directly or indirectly, and because the level of arousal or cerebral activation is altered, there is an influence on alertness, sleep, and waking. Sleep and waking are altered by lesions and stimulation of other regions of the brain.
