When you ask a nurse (or any other ‘helping’ professional) why they do what they do, despite the fact that it is often a thankless task, they might say, “because it is rewarding.” So we can see that some things are rewarding even though they are not pleasurable. Similarly, every hardcore addict will tell you that the part of their addictive cycle which is the most compelling, is not the drug-use itself, but the anticipation of the drug, the wanting of it, which is to say the meaning contained in it. It’s that beautiful moment when your dealer rings you up and tells you that the delivery is here – and all is suddenly well with the world. It’s that transcendent feeling when the drug is in your hand, and best of all when it is lined up ready for take-off, in the pipe, the spoon, or the needle. In this moment – and it is only a moment – we are at peace. The actual using of the drug, for veteran addicts at least, is often anti-climactic.
This model, as I have approximately described it, is known as incentive salience.
The incentive salience model of addiction was first conceived by Kent Berridge, a professor of psychology and neuroscience at the University of Michigan. The word salient means, ‘of the utmost importance’, and so incentive salience hinges upon the idea that incentives (such as drugs) motivate addicted people because they are perceived to be of the utmost importance to them. In this model it is the importance of the goal that is relevant, not the pleasure one feels upon attaining the goal. This model sees the liking of the drug as less relevant than the wanting of it. The enjoyment of the drug is not as pertinent as the desire to acquire it. And this makes a lot of sense when we consider the seemingly irrational behaviour of addicts, who continue to ‘want’ things they don’t ‘like’ anymore.
In fact, Berridge and his colleagues uncovered three distinct but related components of reward — liking, wanting and learning. As we have already discussed, most people tend to think that addiction is all about the first bit — liking (or pleasure). This is an easy mistake to make when we consider how intrinsically pleasurable most addictions are. But even these hyper-rewarding activities are only studded with occasional moments of pleasure, because the brains reward system contains relatively few hedonic hotspots (or pleasure centres).
These hotspots are quite small (anatomically speaking) compared to the much more substantive looms that control wanting and learning. It is also important to point out that feelings of pleasure are activated mostly by neurochemicals like endorphins and endocannabinoids, not by dopamine, as is commonly believed. Dopamine is not a pleasure chemical per se. Dopamine’s job is to power the wanting and learning aspects of reward, and therefore, it is this dopaminergic action that we should be most interested in when we are talking about addiction.
The Role of Dopamine in Addiction
Most of our wanting is driven by sub-cortical processes, by non-thinking parts of the brain, and in particular by dopamine. Dopamine initiates a sense of motivation. Dopamine tells us to go for it. It is the fuel that drives our ‘seeking’ behaviour, and in particular the things that keep us (or our genes) alive. It is dopamine that makes it possible for us to concentrate on important things and fixate on any desired object, goal or end. When such a goal comes into our awareness, particularly a survival goal – but actually anything which is novel – dopamine rewards us by flooding us with salient feelings. It’s worth noting that sometimes these hyper meaningful feelings can be every bit as torturous as they can be enjoyable (such as the feelings aroused by an obsessive love interest for example). Nevertheless, this intense motivation, sometimes enjoyable, and sometimes painful, is how dopamine helps us to work out what is important to us in our environment and what is not.
Dopamine is manufactured in an archaic brain region called the mid brain which itself is part of the brainstem. The brainstem is often referred to as the reptilian brain. This part of the brain is so called because it first developed in reptilian species and is literally the stem out of which our more sophisticated mammalian and human brains evolved. Whenever anything of importance occurs (in survival terms) like the appearance of food or a potential mate, dopamine molecules are released from a bundle of cells called the VTA (Ventral Tegmental Area) and fired up to another cluster of cells called the Nucleus Accumbens. Whenever a good whack of dopamine hits the shell of your Nucleus Accumbens you will feel like something important has just happened.
When people refer to the brain’s ‘reward pathway’ in relation to drug abuse and addiction, it’s usually this fairly crude and ancient section of the brain that they are talking about. And because this brain region is old and well established, it tends to ride roughshod over the more recently evolved brain regions which govern memory, learning and reasoning.
Addiction Affects Our Memory, Learning & Reasoning
Once an initial drug using experience has occurred, it can be judged, learned, and remembered. It can be stored in memory, as useful, or not useful. The happens, by way of positive feedback loops. Positive feedback loops have been the subject of some study in recent years. Engineers who developed social media platforms like facebook, famously hacked into this brain function and exploited it to promote compulsive behaviour in the people using their platforms. But in truth, the positive feedback loop is what lies behind all addictions.
Positive feedback loops work like this. After dopamine has been released from the VTA and hit the wall of the Nucleus Accumbens, the Nucleus Accumbens then sends a signal back to the VTA if it thinks this activity is worth doing again. This signal is a neurochemical thankyou letter in the form of enkaphilins (one of the brains own naturally occurring opiates). This opiate then triggers more dopamine release, and so the cycle goes on until all the dopamine lined up ready to fire at the VTA is used up. At this point the drug user (or anyone involved in a compulsively rewarding activity) will feel catastrophically bored, restless and irritable, because he is ‘dopamine depleted’. One solution to this lethargic state – is to go and get more dopamine!
But here’s the bit that may well mark the difference between those who continue to act obsessively and those who do not.
Another part of the positive feedback loop occurs when the Nucleus Accumbens sends a neurochemical message to a fairly newly evolved brain region called the frontal cortex. This time, the neurotransmitter involved is serotonin, a mood enhancer. When serotonin hits the frontal cortex it delivers a message of “I’m OK”. The frontal cortex is the ‘thinking’ part of the brain. It is highly evolved in humans and endows us with a capacity for self-consciousness and a sense of individual identity. ‘Self-esteem’, could be said to be located in the frontal cortex, or at least, our idea of how acceptable we are and how well we’re doing in relation to other people. Many addicted people don’t have a high self-esteem for numerous reasons (see previous article here) and so when a drug proves to be calming, or medicinal in some way, this serotonergic message to the frontal cortex is very welcome.
In many ways, addiction is a memory and learning illness. Not an illness like Alzheimer’s, which destroys memory, but rather, a condition which ‘re-orders’ memories or prioritizes some memories over others. Addiction is a case of selective memory. For those of us who use drugs or other potent rewards, and experience them as self-medicating – the potent memory of that experience (and the relief that it gave us) hits our ‘emotional brain’ (or limbic system) and drives our desire to do it again. As this cycle continues it becomes more and more ingrained in the thinking parts of our brain (the cortex), as addiction researcher, Bryon Adinoff, has observed:
“The persistent release of dopamine during chronic drug use progressively recruits limbic brain regions and the prefrontal cortex, embedding drug cues into the amygdala…”
In plain English, this means that having found a drug that works for us; one which calms us, energizes us, or otherwise provides some missing need – our brain helps us to remember it and prioritize its use. For people who are lacking in self-esteem, or whose life is very unrewarding, this can be a revelatory experience. So when this happens, the limbic system which governs memory, learning, and emotion, records these events and marks them down as significant: something which might be worth remembering, learning, and then doing again. And this is perhaps the more significant role that dopamine plays in addiction because not only is dopamine a major part of our ‘seeking’ system, it also plays an essential role in building memories. Dopamine bathes those circuits involved in our ‘successful’ behaviours (anything which proved good for our survival) with a strong veneer of meaning, which in turn reinforces the importance and ‘strength’ of those pathways for future use.
In light of the incentive salience model then, the question we should really be asking is: why are drugs so salient to some people and not to others? The answer to this question is nowhere near as obvious as it might first appear, and “because they are pleasurable” is obviously not the answer we are looking for. Everyone finds some form of indulgence pleasurable, but not everyone gets addicted to that source of pleasure.
‘What’ exactly makes an addict is the subject of my next article.
