The neuroscience of addiction

By Mara Costea

Understanding the neurobiological changes that occur in the human brain is the only way in which we can prevent the transition of recreational substance use into a disorder or an addiction. Scientists have simplified the idea of addiction by summarising it into three stages: point of intoxication, denial or withdrawal and preoccupation, which leads to relapse. 

The cycle of drug abuse 

The point of intoxication happens innocently most of the time. For example, the substance can be medically prescribed, but in other cases, the first exposure can appear  due to peer pressure and a desire to fit in. This leads to  the point where the individual has started to use   the drug on a recurring   basis, seeking an  euphoric response. 

The second stage often involves denial, meaning  that when the brain has developed a dependency  on a  drug, it has also learnt to simulate an adequate functioning and no apparent response to it,  even when the drug is consumed in  high doses . This causes the victim of what is now substance abuse to keep increasing the dosage, sometimes culminating in an overdose. . This is the moment when  most addicts end up in rehabilitation facilities  in order to restabilise their lives and heal, but others remain in  a stage of denial. 

Eventually, relapse occurs. Although it does not happen in every case of drug abuse, it is highly common, with 85% of individuals experiencing consumption just one year after treatment. 

The role of dopamine in addiction

The rate of dopamine increase due to drug use is temporary but at high intensity . The prefrontal cortex contains two types of receptors, one having a much greater affinity with  dopamine than the other. In other words, one activates at much lower concentrations of dopamine. An unexpected event (an aspect  in which drug use falls) causes a more/ very  abrupt increase in dopamine levels. This explains why the feeling is so short-lasting and therefore addictive. 

The “reward” effect

The memory processes critical to addiction allow the association of a stimulus with a reward or punishment. When consumers are in an overwhelming drug-use environment, they get a craving, which, as studies suggest, releases at a much higher peak in dopamine levels than when using the drug itself. Moreover, drug abuse damages the dorsolateral prefrontal cortex, which is responsible for decision-making and emotion regulation. This explains the irrational and compulsive behaviours that substance addicts experience. 

A recent study shows that methamphetamine users can upregulate these receptors through regular aerobic exercise, leading to reduced cravings and, consequently, diminished/ less drug use. 

Effects of drug abuse on the developing brain: adolescents and young adults

According to recent studies, the last region of the brain to reach maturity is the frontal cortex, which is responsible for impulse control, risk determination, evaluation of consequences, and decision-making. Moreover, imaging has revealed that the connection between dopamine levels in the frontal cortex of young people is much weaker than in adults, resulting in limited inhibitory/ impulse control. Therefore, there is a concerning rate  of  behaviour that involves uncalculated risks , as well as impulsivity, which means that young people are more prone to experiencing drugs.

References

1. Grace, A.A. 2000. The tonic/phasic model of dopamine system regulation and its implications for understanding alcohol and psychostimulant craving. Addiction 95(Suppl. 2): S119–S128.

2. Baik, J.‐H. 2013. Dopamine signalling in reward‐related behaviours. Front. Neural Circuits 7: 152.
   

3. Volkow, N.D., Tomasi D., Wang G.‐J., et al 2014. Stimulant‐induced dopamine increases are markedly blunted in active cocaine abusers. Mol. Psychiatry 19: 1037–1043.