Sentence:  Since electrical stimulation of the posterior hypothalamus produces the effects of <WSD>wakefulness</WSD> while stimulation of the anterior hypothalamus induces sleep , 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 periodic state during which you are conscious and aware of the world