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You've probably heard about the controversy between the disease model of addiction and the choice model. Stanton Peele, a blogger here on the PT site, waxes eloquent on the topic. You may have even heard that it's a false dichotomy — a position I take myself. But I don't want to waste time trashing the disease model right now. Dr. Peele does that quite nicely. Rather, let's think a bit more deeply about how addicts make choices.
Addiction has an incredibly powerful, self-propelling momentum that takes it beyond the realm of "normal" choice. Yet proponents of the choice model often claim that addiction can be understood without looking at the brain. Wait a minute? Where do we actually make choices, if not in our brains? So if choice becomes highly repetitive, consumed by a focus on short-term gains at the expense of long-term suffering, if choice no longer feels like choice but rather like compulsion, then shouldn't we try to figure out what's going on in the brain at the time?
How brains make choices.
Let's start with "normal" choice. It just takes a moment of reflection to realize that choices are rarely "free." Philosophers debate the very existence of free will, and neuroscientists have shown that we notice making choices some time (up to several seconds) after our brains have already set a particular choice in motion. But let's get down to the basics. Choices involve an exchange between at least two brain regions. The first is the ventral striatum (or nucleus accumbens), a structure that propels us to go after goals that are deemed attractive. In normal choice, this area is responsible for "wanting." In addiction, it seems to be the locus of "craving." The other region is actually a network in the top/middle of the prefrontal cortex, called the dorsal anterior cingulate cortex (or dACC for short). The dACC monitors options, attends to possible consequences, and directs behavior accordingly. The exchange between these regions, sometimes construed as the horse and the rider, takes place in the synapses (connections) that lead from one to the other. Those connections are altered by many aspects of experience: hardship, success, failure, and trauma, to name just a few. Unfortunately they are altered most radically by the cycle of addictive thoughts and behaviors.
Addictive choice.
A troubled neuron.
No two people have the same brain to work with, but there are several neural features that addicts have in common: High levels of dopamine continue to trigger the feelings of craving that spring from the ventral striatum, by strengthening substance-related synapses in that area and weakening synapses that stand for alternative goals. Meanwhile, the dACC's capacity for self-control is actually used up by the recurrent need to inhibit one's impulses. Much like a muscle that gets tired after continuous strain. Given that addiction changes the structure and function of the ventral striatum and the dACC, it must change the basic mechanism for making choices, based as it is on the exchange between them.
Choice can be thought of as an adaptive process. Brains adapt to our experiences, so the choices they make change with time. Addiction is an experience to which brains also adapt, but too rapidly, too thoroughly, and too permanently. Understanding these neural changes is essential for understand how "choice" gets hijacked by addiction. That doesn't make addiction a brain disease. It makes it a kind of corrupted learning, a nasty adaptation. And like any other adaptation, its foundation is the fleshy hardware we carry around in our heads.
Additional posts on similar topics (with more personal and neuroscientific detail) can be found on the Memoirs of an Addicted Brain website and blog.
