Addicted Brains

A neuroscientist examines life on drugs.

The Science of Craving

Psychology tells us that craving is common, but neuroscience tells us why.

Last post, I emphasized the feeling of incompleteness as the foundation of craving. But one reader saw pain relief, relief from suffering, as the fundamental draw. I think both are true. The sense of (relative) completeness that comes from swallowing a cherished pill or drink or piece of cake can be an antidote to suffering—for a while. And the feeling of incompleteness—the sense of a fundamental lack, flaw, or inadequacy—can be a longstanding source of psychological pain.

This is not the time to review Freud in detail, but a hundred years of psychodynamic theory point to the infant's need for milk or food, and the relief it provides, as the primal experience of taking something inside ourselves—something we need in order to be whole. One psychodynamic theorist, Melanie Klein, thought that young children experience a profound longing, which she called "envy," for the mother's breast or the mother herself. The infant seemed to know, beyond any doubt, that he or she needed something outside the self, in order to be complete. Maybe the first few times you got high, or drunk, or laid, you were reminded of how that works.

Psychologists try to measure craving, or desire, using verbal information. For example, Hofmann, Baumeister, and colleagues (2011) got 200 people to participate in an experiment in which they were beeped at random times throughout the day and asked to record whether they were presently experiencing a desire...among other things. To make a long story short, participants reported at least one current desire on 50% of the occasions they were beeped. "On average, desires were actively resisted on 42% of occasions and enacted on 48% of occasions." Well, I'm not sure that puts us much further ahead. Desire is a fact of life, and a lot of desires have to be inhibited. That psychological datum fails the Grandmother Test: My grandmother could have told me that.

Which is why I turn to the brain: the biological basis of mind. I recently heard a very succinct account of what dopamine does in the striatum. It decreases "noise". There are always a number of competing motor plans — plans of action — vying for enactment. That's the normal noise in the system, and that's what maintains psychological flexibility. What dopamine does is to inhibit the weaker plans and disinhibit (augment) the strongest of the competing plans. It's a biological mechanism sort of like focusing our eyes. What dopamine does in the striatum is to narrow the field of potential actions, from many down to one. The competition is quashed and now there's only one goal on the radar. That's the basis of craving: a narrowing of focus and motivation to one thing and one thing only.

Could it be that simple?

There's one other crucial part to the story, and that's the role of cues in addiction. A "cue" is a reminder, an association, that quickly evokes an emotional response (through the amygdala) and turns on the dopamine pump (in the midbrain). According to the research, drug and alcohol cues (like clinking ice cubes or round yellow pills) rapidly increase dopamine flow for addicts. Thus the "plan" to acquire the thing being cued (the drug or drink) is strengthened. Then internal cues—remembering, wishing, imagining—join whatever cue came first, and each of those mental cues also increases dopamine flow to the striatum. From a trickle to a torrent. So, before long, there really is only one plan of action, one intention, one goal that feels worthwhile. And whether or not it's forbidden, it overtakes the prefrontal cortex with its urgency.

Unfortunately, the impact of drug or alcohol cues on the dopamine system gets stronger and stronger with repeated cycles of craving and satiation, so that both the striatum and the prefrontal cortex become modified (through synaptic shaping) to attune more quickly to the promise of relief.

That's how brain science makes craving make sense. Craving...addiction...an aberration, according to the ideals of our society. But a very natural process for a part of our brain whose job it is to motivate us to achieve important goals.

Please also visit my home blog, where a number of recovered, recovering, half-recovering, and not-so-recovered addicts of various substances are developing a productive and friendly dialogue, fueled by personal experience as well as knowledge of the brain.

 

Marc Lewis, PhD has been a professor of developmental psychology and neuroscience for over 20 years and is the author of Memoirs of an Addicted Brain. 

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