Science and medicine are providing new insights into how addictive substances act on the brain and on ways to break their grip, writes Dr Amy Reichelt.
Addictions are difficult to break as we usually surround ourselves with people, paraphernalia or situations that trigger the behaviour that led to the addiction in the first place. But psychological conditioning can be used to break bad habits.
Over a century ago, the Russian physiologist Ivan Pavlov made a discovery that still resonates with both psychological experiments and popular culture. Classical conditioning predicts that by repeatedly pairing a motivationally significant stimulus (such as food) with a particular signal (such as a ringing bell) will result in a conditioned response when the signal is encountered (the bell rings in absence of food).
So the sound of a ringing bell will evoke a behavioural or conditioned response, such as salivation (initially elicited by the food stimulus). A previously neutral stimulus can evoke a particular behaviour through an association with an emotionally significant outcome. Pavlov found that after repeatedly pairing the food with the ringing bell his dogs would salivate just to the sound of the bell.
This theory doesn’t just apply to drooling dogs but has formed an important rationale for the development, maintenance and relapse of drug-taking behaviours. Drugs are rewarding in nature and act by increasing levels of the neurotransmitter dopamine in the brain.
Under normal circumstances, dopamine is involved in maintaining behaviours essential for survival, such as obtaining food and sex. Drugs also act on this system and the brain associates the rewarding high with the drug, motivating more drug taking. These systems become “hijacked” by the drugs of abuse, producing maladaptive changes that preserve addictive behaviours.
Lighting up and learning
Nicotine, via tobacco, is one of the most heavily used addictive drugs in the word. In Australia, smoking is the leading preventable cause of death, killing about 15,000 people every year. Quitting smoking is difficult, and nicotine withdrawal symptoms include irritability, anxiety, difficulty concentrating and insomnia.
Nicotine exerts physiological effects very rapidly. Nicotine from inhaling a cigarette reaches the brain in about 10 to 20 seconds and there it binds to nicotinic receptors on neurons.
Stimulation of nicotinic receptors affect functions such as breathing and heart rate, and triggers the release of dopamine. So the rewarding effects of smoking are very rapid. And the association between smoking and its rewarding effect is very strong, and forms quickly.
Classical conditioning theory predicts that drug-related stimuli can become associated with the rewarding aspects of using. These include drug paraphernalia (cigarette packets, syringes, bongs and pipes) and environments where drug taking occurs. These stimuli can evoke responses, such as craving and drug seeking, which is known as second-order conditioning.
For smokers, just the sight of a cigarette packet can evoke the feeling of wanting to smoke. But this isn’t restricted to smokers and drug addicts. We form associations with all kinds of environmental stimuli and things we desire. Just looking at your smartphone, for instance, can create an urge to check email.
These complex associations maintain behaviours and can also cause reinstatement when certain cues are encountered. This is why smokers find it so difficult to quit – the environment is full of signals associated with smoking cigarettes.
Breaking the habit
A prescription medication treatment for smoking addiction is Varenicline (known as Champix in Australia, Canada and Europe and Chantix in the United States). Varenicline is a partial agonist at nicotinic receptors – it stimulates nicotine receptors more weakly than nicotine does.
This reduces cravings for nicotine and decreases the satisfying effects of cigarettes because the receptors are already occupied with the varenicline molecules, so nicotine can’t exert its full effect. It decreases the rewarding effect of smoking and weakens the association between cigarettes and pleasure.
Varencline has a success rate of about 22%, which is greater than Buproprion (Zyban), another smoking cessation aid. But concerns have been raised about the potential side effect of depression in both of these treatments.
Another reported effect of varenicline in some people is nausea, which can reduce smoking more rapidly because the taste of tobacco becomes associated with nausea. This is called conditioned taste aversion.
Varenicline as a smoking-cessation treatment may seem extreme, but its rationale is firmly established in Pavlovian learning theory; a behaviour will decrease when its reward is devalued. And if the behaviour becomes associated with something negative (such as feeling nauseous), it will occur even less.
We are fortunate that advances in medicine offer smokers more choices than ever before to help them quit successfully. Some may seem more extreme than others but they’re all centred on breaking the nicotine habit.
Dr Amy Reichelt is research fellow in neureoscience in the UNSW School of Psychology.