Sentence:  Since electrical stimulation of the posterior <WSD>hypothalamus</WSD> 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:  a basal part of the diencephalon governing autonomic nervous system