Sentence:  Since electrical stimulation of the posterior hypothalamus produces the effects of wakefulness while stimulation of the anterior hypothalamus induces <WSD>sleep</WSD> , it may be said that the reactivity of the whole organism is altered by a change in the autonomic reactivity of the hypothalamus . 
Meaning of the word marked with <WSD> tags:  a natural and periodic state of rest during which consciousness of the world is suspended