The Habit of Addiction

ResearchBlogging.orgAny form of addiction can become a vicious circle. From an outsider’s point of view, drug addiction may seem like a completely irrational behaviour why on Earth would anyone want to spend money on something so damaging and dangerous? But for regular drug users this question, while still present, is no longer interpreted in the same way and it is not because they chose it so but because the drug abuse has tweaked the brain circuits responsible for survival instinct.

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Cocaine is one of the most commonly abused drugs, 1-3% of people in the developed world use cocaine. The addiction to cocaine is the outcome of deregulation of dopamine in the brain. Dopamine is a molecule that neuronal cells in the brains use to communicate with each other. One neuron makes dopamine and releases it while another nearby neuron takes it up. The uptake of dopamine leads to electric signalling in the brain and activation of pathways in responsible for motor functions, learning, behaviour, pleasure, etc. The precise control of the amount of dopamine in the brain at any given time is crucial for correct functioning of these pathways. However, the presence cocaine in the brain disrupts dopamine balance. Specifically, cocaine prevents re-uptake of excess dopamine by the dopamine producing cells, which leads to an excess stimulation of receiving cells.

The limbic system (fig.1), also sometimes called the reward system, in our brains is one of the sites where dopamine is the main molecule involved in signalling. In simple terms, if you are thirsty and drink a glass of water it is the limbic system that makes you feel the pleasure of that refreshing liquid. Limbic system is an evolutionarily ancient system intrinsically linked to pleasure and survival behaviours in animals. Therefore, messing up its normal functions, such as normal dopamine levels, may lead to dire consequences. Having an excess dopamine (e.g. as an outcome of cocaine use) in the limbic system in short-term leads to great pleasure and euphoria, however in long-term excess dopamine leads to behavioural changes, inability to associate actions with rewards and punishments, and memory impairments. An extreme example of these long-term changes can be seen in cocaine addicted lab animals which choose to seek out the drug and ignore any other food to the point of starvation.

Fig. 1. The limbic system in suman brain
Fig. 1. The limbic system in human brain

Animal behaviour is goal-driven, that is we adjust our actions depending on their outcomes. I help you now and you will help me later, or I help you now and you may not help me later but it gives me a great pleasure to do it anyway, so the outcome, even if unconscious, is still positive*. But is this goal-driven attitude still in contact in context of cocaine abuse? Well, it seems not quite so. A recent study investigating this question saw that cocaine abusers are more likely to be habit than goal driven. In the study a group of cocaine addicted people was given tasks that involved association between particular stimuli and outcomes. The first task was association between an animal in the picture and the fact that if you click on a picture with an animal rather than a blank screen you are given money. While it was clear that overtime cocaine addicts were able to associate the action with reward better, they learned this association significantly slower than a control non-addict group (fig.2). Same results were seen if the outcome was something to be avoided. The participants in the study were allowed to learn by trial and error an association between a picture and an electrical shock and had to press the correct pedal in order to avoid the shock. Again the drug users were persistently slower at making the connection between the action and reward (fig.3).

Fig.2. It is harder to associate image of an animal with reward in points for cocaine users compared to healthy controls.
Fig. 2. It is harder to associate image of an animal with reward in points for cocaine users compared to healthy controls.

 

Fig.3. An ability to associate a negative outcome (an electric shock) with an image is also impaired in drug users.
Fig. 3. An ability to associate a negative outcome (an electric shock) with an image is impaired in drug users.

Not only learning of reward association but also adjusting in the case of reward change was slower in drug abusers. When study participants were taught to associate a picture with monetary reward and then the conditions where unexpectedly changed so that the reward was no longer given for identifying the picture the drug-user group continued to respond to stimulus with no award more often while healthy individuals were quick to make a change (fig.4).

Fig.4. It is harder to change the behaviour for cocaine users if an image no longer leads to reward in points.
Fig. 4. It is harder to change the behaviour for cocaine users if an image no longer leads to reward in points.

Various other tasks and comparisons with different drug users and healthy individuals in the same study, suggested that cocaine abusers are more prone to impulsive behaviour, their motivation to preform well is decreased and that overall they are more inclined towards habit-driven learning and not a goal-oriented one.

The observations in this study highlight the difficulties of treating cocaine addiction. If goals in life are not perceived in the same way and habits rather than rewards from outcomes are what influence a person’s behaviour, any kind of motivational intervention (e.g. I go through this struggle now in order to have a better future) may have very little positive effect. Perhaps concentrating on forming the right habits and avoidance of any habitual stimuli would be a better approach, however, our habits are often influenced by our surroundings, which may mean that a top-to-bottom change in life is the only way to go.

*Side note: that’s why feedback is so important for anything we do in life. Feedback is a way of interpreting the outcomes of our behaviours and then adjusting them to improve the outcome next time and achieve greater goals.

Ersche KD, Gillan CM, Jones PS, Williams GB, Ward LH, Luijten M, de Wit S, Sahakian BJ, Bullmore ET, & Robbins TW (2016). Carrots and sticks fail to change behavior in cocaine addiction. Science (New York, N.Y.), 352 (6292), 1468-71 PMID: 27313048

Nestler, E. (2005). The Neurobiology of Cocaine Addiction Science & Practice Perspectives, 3 (1), 4-10 DOI: 10.1151/spp05314

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