More than 40,000 people in the UK crave drugs and alcohol compulsively. And this happens at the expense of the harms associated with its long-term use, be it physical, such as withdrawal, or behavioural, such as quitting one’s job or alienating from friendships.
Since any of those are unlikely to be on anyone’s bucket list, why do people get caught in this trap? Throughout history, drug and alcohol addicts have been regarded as either sinners or criminals, receiving punishment from the Church or the court. That was until the 19th century, when addiction was proposed as an explanation in itself for substance abuse. In the 1950s, the World Health Organisation regarded alcohol and drug addiction as a disease, recognising that those who are addicted cannot control their behaviour. Yet this theory did not explain how one comes to get this ‘disease’ in the first place, thus this explanation had to be refined.
Drugs influence the activity of neurotransmitters. They work to either excessively stimulate their action or, on the contrary, to over-inhibit their effect. Different drugs can affect neurotransmitters in different ways – they can stop them from being recycled back into the transmitting neuron, act on the cell to release abnormal amounts or even mimic their effect.
After repeated drug abuse, the cell’s firing rate can become abnormally high or low. This kind of cell activity can damage the cell and lead to its death, but thanks to an inbuilt mechanism, the cells adapt to protect themselves. Cells reduce their receptor sites so that less neurotransmitters can manage to bind to the receiving neurons. This way, neurotransmitters have a diminished effect on exciting the cells (or inhibiting them, depending on the drug and neurotransmitter type). Alternatively, the existing receptors will no longer be sensitive to these neurotransmitters. Even if neurotransmitters do bind to receptors, this will not contribute to exciting or inhibiting the cell.
As a result of these changes, a drug user would not experience pleasure as usual, hence the depression and lack of motivation in addicts. They would experience discomfort in the form of withdrawal. Take heroin for example. It leads to euphoria and relaxation, among other effects. The withdrawal symptoms come in the form of dysphoria and agitation. One theory for addiction states it is withdrawal that brings the addict back to drugs. In other words, addicts take drugs simply to avoid the negative symptoms of withdrawal. This was the first theory for addiction classified as ‘scientific’.
The withdrawal hypothesis has lost popularity with the advent of the positive reinforcement theory. This theory highlights the evolutionary importance of the reward system. The reward system will work to ensure that behaviours that are necessary for survival will be repeated or reinforced. Activities such as eating or having sex are made to be pleasurable so that we do them again.
Drugs, on the other hand, hack this mechanism. They activate the reward system artificially. This means that behaviours linked to taking the addictive drug will happen more often, as they are being associated with a positive outcome. We can observe how the brain can get addicted to behaviours that activate the reward system in rats implanted with microelectrodes. In one study, the microelectrode was placed in one of the regions which is active during a cocaine high, the ventral tegmental area. By the press of a lever, they could stimulate this area themselves. Stimulation would lead to an outburst of dopamine in the mesolimbic system. An additional lever was present, which they associated with food.
Rats pressed the lever for electric shock as often as 2000 times per hour, leaving food aside. After one day, they had to be disconnected from the apparatus to prevent death from starvation. But that was not the case for rats which had stimulation on the neocortex, the outer surface of the brain. These rats pressed the shock lever randomly. Clearly, pressing this lever produced no reward. The fact that a rat could get addicted to an electric shock sends a loud message: over-stimulation of the reward system can easily lead to addiction.
Next time you fancy taking drugs, bear in mind that your brain is going to make a few changes. It may even need a little extra support to generate pleasure sensations in the future. And sometimes, such changes are irreversible.