Wanting happens in nearby, but distinct, circuits. These are more widely spread around the subcortex than the liking circuits, and use a different chemical messenger system, one based around a neurotransmitter called dopamine. Surprisingly, it is this circuit rather than the one for liking which seems to play a primary role in addiction. For addicts, a key aspect of their condition is the way in which people, situations and things associated with drug taking become reminders of the drug that are impossible to ignore. Berridge has hypothesised that this is due to a drug’s direct effects on the wanting system. For addicts any reminder of drug taking triggers a neural cascade, which culminates in feelings of desire, but crucially, without needing any actual enjoyment of the drug to occur.
The reason wanting and liking circuits are so near each other is that they normally work closely together, ensuring you want what you like. But in addiction, the theory goes, the circuits can become uncoupled, so that you get extreme wanting without a corresponding increase in pleasure. Matching this, addicts are notable for enjoying the thing they are addicted to less than non-addicts. This is the opposite of most activities, where people who do the most are also the ones who enjoy it the most. (Most activities except another Christmas tradition, watching television, where you see the same pattern as with drug addictions – people who watch the most enjoy it the least).
So now you know what do when you find yourself chomping your way through yet another packet of crisps over the holiday period. Watch your face and see if you are licking your lips. If you are, perhaps your liking circuits are fully engaged and you'll be happy with what you’ve eaten when you’re finished. If there's no lip-licking then perhaps your wanting circuits are in control and you need to exercise some self-restraint. Maybe after the next mouthful, though.