• Booze, Weed and the Human Brain

    A study by Rachel Thayer and colleagues from the Universities of Boulder, Colorado and Portland, Oregon, published recently in the journal Addiction revealed some fascinating differences between the impact of recreational alcohol and cannabis use on the structure of the human brain.

    It was known from previous research that the more alcohol an adult regularly drinks the greater the degree of shrinkage of the brain’s grey matter. The grey matter is the folded outer surface of the brain that makes it look a bit like a walnut. This is where neurons interface with each other by means of synaptic connections at which one neuron can exert an influence on another. It is the networks of neurons bringing information together within the grey matter that allows computations to be performed so that we can perceive the world via the senses, feel emotions based on our interactions with other people and execute purposeful behaviours like decision making, problem solving and voluntary movements. So, as a rule of thumb, the lower the volume of space occupied by a person’s grey matter, the greater the reduction in computational power.

    This new study looked at not just the link between boozing and grey matter but also investigated whether it had any impact on the white matter too. White matter is the neuronal cabling along which electrical messages are ferried to and from different patches of grey matter in different parts of the brain’s cortex. Grey matter in the occipital lobe at the back of the brain, which crunches sensory information coming in through our eyes, can send messages to the prefrontal cortex via white matter pathways, and vice versa. Grey matter in the left side of the brain can send information to and receive information from right hemisphere cortical areas via white matter connections that run through the corpus callosum (this is a thick bundle of white matter connecting the left and right halves of the brain).

    These white matter pathways contain the neuronal axons, which is the cabling through which electrical pulses (called action potentials) are passed between neurons. These axons are wrapped in electrically insulating myelin fibre which speeds up the transmission of action potentials. Damage to this insulating layer can be detected with a certain type of MRI scan and is formally described as ‘reduced white matter integrity’. Thayer and colleagues’ findings showed that the more alcohol people routinely drank the greater the impact on grey and white matter. High alcohol consumption is associated with reduced grey matter volume AND white matter integrity.

    That’s not all. They also looked at the differences between adult brains (20-55 years old) and adolescent brains (14-19). While high alcohol intake way associated with reduced grey matter volume in the adolescent brains, they didn’t find any evidence of reductions in white matter integrity. Presumably if those teens carried on their high alcohol intake, they would end up damaging their white matter like their older counterparts.

    Perhaps the most surprising thing about this study is that, across over 400 teens and more than 800 adults, they found no evidence of any link between the amount of cannabis consumed in the 30 days prior to brain scanning and the grey matter volume or white matter integrity. This suggests that despite alcohol being legal in the UK and cannabis being illegal, from the perspective of the impact of these commonly used recreational drugs on two different important aspects of brain structure, the relevant laws may well be working in direct opposition to the degree of harm caused, both to the individual and society as a whole.

    If you enjoy these blogs then you’ll love my 2 series of Secrets of the Brain in Ultra High Definition (www.insight.tv / Sky Channel 564). This story was covered on episode 90 of my fortnightly Geek Chic’s Weird Science podcast available on iTunes, Acast, Libsyn and Podbay. I dig around on the internet on a daily basis for articles on the very latest breakthroughs in neuroscience research and, when I find something interesting, well-written and relevant, I post it on Twitter (@drjacklewis). Most excitingly of all, from the 12th July 2018, my new book – The Science of Sin: Why We Do The Things We Know We Shouldn’t – will be available in all good bookshops.

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