As the holiday season approaches, Tom Stafford looks at festive overindulgence, and explains how our minds tell us we want something even if we may not like it.

Normally wanting and liking are tightly bound together. We want things we like and we like the things we want. But experiments by the University of Michigan’s Kent Berridge and colleagues show that this isn’t always the case. Wanting and liking are based on separate brain circuits and can be controlled independently.

The liking system is based in the subcortex, that part of our brain that is most similar to other species. Electrical stimulation here, in an area called the nucleus accumbans, is enough to cause pleasure.

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.