Lower Brain To Blame For Greater Propensity For Drink, Drugs

Smarter people may be more prone to imbibe or alter the mind with illicit substances, behaviors deemed novel by evolutionary standards. Capping more than 40 years of research, a 2011 study of British people followed since the 1970s showed that children with higher IQs matured into thirtysomethings more likely to drink, smoke marijuana, and consume other drugs, in results consistent across socioeconomic lines and independent of psychological stressors from childhood.

Yet, a new study examines differences not in the prefrontal cortex but in the limbic system, a complex set of structures closer to the brainstem and to the evolutionary past. In the November issue of Hippocampus, Montreal neuroscientist Veronique Bohbot reports an association between higher rates of drinking and drugging and greater reliance on one of two primary learning strategies: stimulus-response, a form of rote learning acquired from traveling along the same route on a regular basis, one that becomes habit.

Greater Propensity For Drink, Drugs Found In Lower Brain Among 55 study subjects, those with a stimulus-response learning style associated with a more developed striatum in tandem with a smaller hippocampus, were more likely to drink and to take drugs. Shutterstock. http://jech.bmj.com/content/early/2011/10/28/jech-2011-200252.abstract?sid=db52aed3-324c-4d3d-b40c-4b6a121d220b

Such people may depend more upon stimulus-response strategy with greater development of the striatum along with a smaller, weaker hippocampus. Those with more a more developed hippocampus tend toward a style of learning called spatial strategy, wherein the brain develops cognitive maps based upon visual cues and landmarks.

“The literature indicates that children engage in stimulus-response strategies from a very young age,” Véronique Bohbot says. “Reward-seeking behavior in childhood, especially for immediate rewards like candy or playing action video games, stimulates the striatum and encourages stimulus-response strategies during navigation. This would predispose the child to drug seeking behaviour.”

In the study, Bohbot and her like-minded colleagues tested 55 healthy young adults by assessing their navigational strategies with a virtual maze shown previously to separate the two different learning styles, using two different parts of the lower brain. “We have shown that spatial learners have increased grey matter and [functional magnetic-resonance imaging] activity in the hippocampus compared with response learners, while response learners have increased grey matter and fMRI activity in the caudate nucleus,” of the striatum, she said.

Among those with more striatum and less hippocampus were longer histories of cigarette-smoking and marijuana use, in addition to twice as much alcohol consumption.

Bohbot, of the Douglas Mental Health University Institute, plans to present her findings this month at the annual meeting of the Society for Neuroscience in San Diego, where she’ll advocate for placing greater importance on the improvement of spatial-navigation skills to maintain a healthier, more balanced style of cognition.

Underdevelopment of the hippocampus, Bohbot says, is linked not only to greater likelihood of drinking and drugging but to increased risk of developing mental illnesses such as schizophrenia, depression, post-traumatic stress disorder, or Alzheimer’s disease.

 

Source: Bohbot, Veronique D., Del Balso, Daniel, Conrad, Kate, Konishi, Kyoko, Leyton, Marco. Caudate Nucleus-Dependent Navigational Strategies Are Associated With Increased Use Of Addictive Drugs. Hippocampus. 2013.

White, James, Batty, David G. Intelligence Across Childhood In Relation To Illegal Drug Use In Adulthood: 1970 British Cohort Study. Journal of Epidemiology and Community Health. 2013.

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