releases those same hormones, it overwhelms the reward system, and if it continues, it can spark long-lasting changes in the brain. That is what addiction truly is: the brain physically changing in response to something unnatural, in ways that can alter how a person thinks and processes information. Worse, tolerance builds, leaving the person chasing the same flush of hormones again and again.
At this point, it is not a question of willpower, but one of a serious illness.
A study: substances and memory
A study by the Department of Psychology and the School of Psychological Sciences at the University of London investigated how recreational substance use affects autobiographical memory— the store of memories from one’ s own life— which is coordinated by neurotransmitter communication networks.
The study involved 100 adults aged 18 to 55: 47 non-users and 53 substance users. All completed questionnaires and an autobiographical memory test. Substance users recalled significantly fewer personal-event memories than non-users, and left more questions unanswered within the time limit. These differences persisted even after accounting for covariates such as general health, sleep and alcohol consumption— suggesting recreational substances do affect neurotransmitter networks, and that autobiographical memory is strongly influenced as a result.
Human relationships, though, are far more complex than those between rats, which makes studies like Rat Park a simplification of the real nuances of human interaction. Rats have a less developed prefrontal cortex— the region responsible for decision-making— so the leap from rats to humans is already strained. With more complex decision-making, humans may have more complex reasons for using drugs, such as past trauma or ongoing mental-health issues, and in some societies drinking or drug use is woven into culture and socialising. To make the experiment more relevant to human recovery, it would be interesting to move rats that had been isolated into the Rat Park, and see whether their dependency decreased.
Conclusion
Drugs affect neurotransmitters— and some mimic their shape— which can be deeply harmful, because the reward system that evolved to help us survive becomes overloaded. This is increasingly recognised as a chronic illness or brain disease, and it deserves to be discussed as one. Studies using rat brains raise ethical problems, since the animals cannot consent and may suffer lasting harm; and while rats resemble humans neurologically, they are not identical— especially in scale— so addiction cannot be fully explained through their brains alone.
Ethical constraints: the limits of rat brains
Many studies of cognitive function use rat brains as a substitute for human ones. Rats seem a more ethical and accessible alternative— but how accurate are they as models of human addiction?
One of the most famous rat studies is the“ Rat Park” series run by Bruce K. Alexander and colleagues in the 1970s. Rats were placed in one of two conditions. Some were isolated and offered a choice between plain water and drug-enhanced water( a morphine – hydrochloric solution).
References
01 EMOTIV( 2017). Cognitive Neuroscience: Definition, Brain Structures & Functions.
02 Yale Medicine( 2022). How an Addicted Brain Works.
03 Levent, A. & Davelaar, E. J.( 2025). Recreational substance use is linked with difficulty in recalling personal experiences. Scientific Reports, 15( 1).
04 Alexander, B. K. et al.( 1981). Effect of early and later colony housing on oral ingestion of morphine in rats. Pharmacology Biochemistry and Behavior, 15( 4), 571 – 576.
05 Pinjala, P. et al.( 2023). CRISPR / Cas9 assisted stem cell therapy in Parkinson’ s disease. Biomaterials Research, 27( 1), 46.
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