Heroin and cocaine addicts become hooked because different parts of the brain become worse at communicating with each other, according to new research.
Addicts’ brains contain less white matter than people who do not take the class A substances, say scientists.
White matter connects everything in the brain together and helps to transmit signals.
Researchers have previously found less white matter in drugged-addicted animals in the lab but the new study is the first to suggest human addicts’ brains also contain less of it.
Academics in the US studied the links between the prefrontal cortex, a part of the brain which enables us to perform everyday tasks and affects our personality, and the habenula, a region that plays a critical role in our understanding of risks and rewards.
The habenula has been found to be a driver of addiction in animals.
Signalling from the prefrontal cortex to the habenula is disrupted in cocaine-addicted rodents, suggesting it plays a role in withdrawal and relapse.
The team say this pathway is still not well understood in humans.
For the study, researchers used MRI scans to investigate the prefrontal cortex- habenula pathway in human heroin and cocaine addicts and a control group of healthy people.
In cocaine addicts, they found white matter had degenerated in that pathway.
People who had recently stopped taking cocaine and heroin addicts also had an impaired pathway.
The study’s first author, Sarah King, a PhD student at the Icahn School of Medicine Mount Sinai, New York, said: “Abnormalities in this path may be generalised in addiction.
“Importantly, we found that across all addicted individuals, greater impairment was correlated with earlier age of first drug use, which points to a potential role for this circuit in developmental or premorbid risk factors.”
The findings were published in the journal Neuron.
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