• 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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  • Adolescent Brains in the 21st Century by Dr Jack

    I was once told that adolescence is the hardest thing I would ever have to do in life. Up to that point in time I had got the overwhelming impression that most adults wished they could go back to the simple life they seemed to distinctly remember enjoying during childhood. All this smacked of rose-tinted glasses to me, but still I asked myself what exactly was I doing so wrong to find the teenage years a bit of a grind.

    Teenagers tend to experience life in the extreme. The highest highs rub shoulders with the lowest lows. They tend to experience everything as either fabulously exciting, depressing, or mind-numbingly boring, with very little in between. There are a variety of reasons why this is the case:

    • during adolescence the brain is a patchwork quilt of work-in-progress (see video below)
    • it is undergoing a neurochemical conspiracy that simultaneously amplifies emotions
    • whilst encouraging risk taking and exaggerating perceived benefit

    …all in the absence of any extensive experience that, in adults, can occasionally step in to trump the usually erroneous risk/benefit calculations that accompany every decision at an unconscious, implicit level.

    I personally found the acknowledgement that being a teen is tough to be profoundly reassuring. Now as a neuroscientist I can go one step further by actually showing WHY being a teenager will always feel tough at times. More importantly I will describe why teenagers of today will turn into adults that are even more different from the previous generation than ever before in the history of man.

    Human brain maturation does not reach completion until after adolescence. During the teenage years the brain is literally caught midway between adulthood and childhood. In the mid-teens cerebral maturation looks like a patchwork quilt, with some areas that have already reached their adult form intermingled amongst others that have not changed significantly since childhood. Yet other regions of cortex find themselves in a transition state part way between the two extremes. This is why a teenager can seem so bright and intelligent one minute, whilst making the most disasterous decisions and over-reacting in the most outrageous emotional outbursts the next. There is a child and an adult co-existing in the brain of a teen. Below is a video that tracks the brain’s maturation over the course of adolescence starting in the early teens and ending in late teens (blue colour = mature cortex; so keep an eye out for how much green, yellow, orange and red is still in the mix throughout most of adolescence).

    The process of adolescent brain maturation, counterintuitively, does not involve an increase in the thickness of the brain’s outer surface (the cortex). On the contrary, it actually involves a reduction in cortical thickness – as less important synaptic connections and brain pathways are “pruned” away; presumably to free up resources for more intensively-used neural networks. This process enables the brain to function more and more efficiently the more certain behaviours are repeatedly performed and elaborated upon. Skills that we acquire with a great deal of time and effort during childhood are performed effortlessly by the time we reach adulthood.

    The human brain will adapt to any environment with which many, many hours are spent interacting. These days the real life immediate environment of a teenager’s home, school, playground, social settings etc in which they spend their waking hours is increasingly supplemented by a wide variety of virtual and online spaces and places into which innumerable hours are poured. This means that digital natives – kids that cannot remember a time before the internet – are going through their “synaptic pruning” maturation phase of accelerated teen brain development synergistically with virtual, as well as real, worlds. The brains that result from this interactive process will be specialised differently to those honed during a twentieth century adolescence.

    Cause for alarm? Well, maybe yes, maybe no. It will undoubtedly be a mixed bag. Brain specialisation to improve efficiency in the execution of one behaviour will always come at the expense of specialisation that could have been invested in something else. This is displacement.

    When time spent playing massive multiplayer online games (MMOG) entirely displaces time spent engaging in old fashioned face-to-face interaction with a friend or group of friends certain brain areas will be improved in preference to others. That teenager would develop superior visuospatial, rapid task-switching and quick decision making abilities, but at the expense of social skills; unless time is also invested in extensive face-to-face communication with peers. Social networking and instant messenging services actually takes this social displacement to a whole different level by actively disrupting what little time is acutally spent in the company of real people.

    Teen social lives are increasingly becomeing less about the face-to-face and much more about face-down-to-phone. The right to choose which smartphone alerts they do and don’t respond to are waived in favour of a slavish dependency. The attention of many teens is immediately diverted to any BBM, Twitter, Facebook etc alert that squarks and vibrates from their smartphone – regardless of where they are or who they are with. This constant disruption must surely degrade the quality of in person social interaction and brain specialisation supporting this vital skill. So does this mean the art of conversation is utterly doomed?

    If teens can be made aware of the need to take control of their digital consumption then there is hope. Otherwise they’ll find themselves distinctly uncomfortable being in the same room as other people and will much prefer to communicate through the written word – a scenario that will inevitably leave them feeling empty. Brains that evolved to communicate much more effectively through body language than speech will inevitably miss the physical presence of another person when communication becomes exlusively remote. Not to mention the fact that physical touch is one of the primary ways in which a brain is inspired to activate brain circuitry that makes a human being feel safe, secure and content.

    In addition to these monthly brainposts you can catch daily #braintweet by following me on Twitter.

    Please don’t leave a comment (spambot overload) but I would love to hear from you so please do send me an email.

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  • What Goes On in a Teenage Brain? by Dr Jack Lewis

    At the onset of puberty the grey matter reaches maximum thickness and that key process of maturation, neuronal pruning, begins in the adolescent brain. This process does not occur uniformly across the whole brain but instead starts at the back of the brain and gradually progresses towards the front over a period of several years. Research at the National Institute of Mental Health in the US has tracked these changes using MRI to create a colour-coded animation that gradually progresses from an early teenage brain to a late teenage brain with red indicating where the grey matter is thickest, yellow a little thinner, green a little thinner again and finally the thinnest (and most mature) brain areas in blue:

    If you pause the video after about 2-3s you can see the status of the brain in the mid-teens – it is quite literally suspended half way between the adult and child form – some brain areas have fully matured by this point in life (blue), but there is a vast patchwork of reds, yellows and greens indicating many brain areas that are still in their childlike form. If you re-start the video you’ll notice right at the end the very last brain area to go from “almost mature” green to “fully mature” blue is at the front of the brain, within the prefrontal cortex. The dorsolateral part of the prefrontal cortex (the upper side parts of the brain region residing behind your forehead) is responsible for impulse control in the mature fully developed brain.

    Adults who have brain damage in areas of the prefrontal cortex lose their ability to control their anger – reacting in a highly aggressive manner at the slightest provocation. Remind you of anyone? When the hormones of adolescence are running riot, teenagers can often find themselves in situations that induce feelings of helplessness and frustration, which invariably finds expression as anger. This happens because prefrontal brain areas that are used to exert control over impulsive behaviours in adults are not yet fully developed. The important thing to remember is that late development of these important brain areas is not necessarily a mistake and may not, frustrating as it may be for the poor, long-suffering parents, be a bad thing. The inability of teens to control their aggression and arguments that their crankiness causes may actually help to break reliance on parental support, encouraging them to test the waters of independence in preparation for independent adult life.

    In addition to these brainblogs you can follow Dr Jack on Twitter to catch his daily #braintweet.

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