Sentence:  Moreover , the dominance in parasympathetic action ( with reciprocal inhibition of the sympathetic ) at the hypothalamic level induces , by its peripheral action , the autonomic symptoms of sleep and , by its action on the cortex , a <WSD>lessening</WSD> in the reactivity of the sensory and motor apparatus of the somatic nervous system . 
Meaning of the word marked with <WSD> tags:  a change downward