Sentence:  Since electrical stimulation of the <WSD>posterior</WSD> hypothalamus produces the effects of wakefulness 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:  located at or near or behind a part or near the end of a structure