Sentence:  The conceptual framework of opponent process <WSD>counteradaptation</WSD> involves an initial "a-process" (positive hedonic effect; "light side") occurring shortly after presentation of the reinforcer followed by a "b-process" (negative hedonic effect; "dark side") appearing after the a-process has terminated. 
Meaning of the word marked with <WSD> tags:  The development of tolerance; the adaptation of the body's homeostatic mechanisms to counteract a drug effect.