Sentence:  Since electrical stimulation of the posterior hypothalamus produces the effects of wakefulness while stimulation of the <WSD>anterior</WSD> 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:  of or near the head end or toward the front plane of a body