I love this definition, because we feel the absence and want to resolve it. If the focus on that absence gets too great, we start living to serve the reduction of that absence, leading to antisocial behavior the deeper you step into the addiction.

I also believe this is one reason why we are so easy to addict these days - we feel the absence of meaning in our lives (which used to be filled by spiritual practices that many have abandoned all over the world) and in an effort to reduce that lack of meaning, we seek meaning in other things. And if not meaning, we seek comfort which can lead to addiction to anything we rely on too much to salve the pain.

This is a philosophical take rather than a biochemical one, of course, so there are multiple angles to consider this issue from.