Hard Evidence: Is the teenage brain wired for addiction?

The younger you are when you have your first alcoholic drink, the more likely you are to develop problems later on in life.

As a nation, we are drinking much more than we used to, which is partly attributable to alcohol being cheaper and more available than ever. Many British teenagers get into the habit early, although recent trends suggest this situation is improving (alcohol consumption among teenagers is slightly lower than it was ten years ago).

Nonetheless, drinking alcohol during adolescence is not a good idea, because the younger you are when you have your first alcoholic drink, the more likely you are to develop problems later on in life. The same is true for cigarette smoking and the use of illicit drugs such as cannabis and cocaine.

Rates of teenage drinking are dropping. NatCen

 

Arrested development

Why are adolescents particularly vulnerable to addiction? A large part of the answer comes from our understanding of the neurobiology of brain development during adolescence. The brain does not reach maturity until fairly late in life, with new connections between brain cells being formed right up until people are in their mid-20s.

Importantly, the brain does not mature at a uniform rate. The more primitive regions of the brain, including the reward system and other areas of the subcortex such as those parts that process emotions, reach maturity relatively early (when people are in their early teens).

The prefrontal cortex is a late bloomer. National Institute of Health

The more “advanced” parts of the brain, such as the prefrontal cortex, are not fully developed until much later. In behavioural terms this means adolescents are particularly sensitive to their emotions and to things that are novel and motivationally appealing, but they are relatively unable to control their behaviour and plan for the future.

Taking risks

My research suggests this can explain why some adolescents drink more than others: teenagers who were relatively poor at exerting self-control, or who took more risks on a computer test of risk-taking, were more likely to drink heavily in the future.

This creates perfect conditions for vulnerability to addiction during adolescence, because the motivational “pull” of alcohol and other drugs is very strong, whereas the ability to control behaviour is relatively weak. Many scientists think if adolescents do drink a lot, and if they do it frequently, then this might cause long-lasting changes in the way that the brain is organised, which can make it very difficult to stop drinking.

We certainly see changes in the brains of people with alcohol problems (compared to people without problems), but it can be difficult to work out if alcohol caused those brain changes, or if those people had slightly different brains before they started drinking, and these subtle differences may have led them to start drinking in the first place.

Starting early carries greater risk. NatCen

 

Addiction and behaviour

In principle, adolescent brains could be vulnerable to “behavioural” addictions as well as alcohol and drug addiction, for exactly the same reason. Very few behavioural addictions are officially recognised by psychiatrists and psychologists at the moment (gambling addiction is the only exception).

The Channel 4 documentary Porn on the Brain shown this week asked whether pornography is addictive, and if adolescents could be getting hooked. As shown in the programme, it certainly seems to be the case that a minority of adolescents who use pornography exhibit some of the characteristic features of addiction, such as feeling unable to control their use of porn, and loss of interest in other activities.

Their patterns of brain activity when viewing porn seem to be similar to those seen in people with alcohol and drug addictions when they look at pictures of alcohol and other drugs. It remains to be seen whether addiction to porn will eventually be recognised as a psychological disorder, but it is clear that it can create problems for some adolescents and young adults who use it.

What can be done? Although it’s obvious, parents should do what they can to prevent their children from experimenting with alcohol, smoking and other drugs for as long as possible. The same applies to other things that might eventually be considered “addictive”. School-based prevention programmes can also be successful, including a recent program that is tailored to different personality types and has shown some promise at reducing alcohol consumption in teenagers.

Hard Evidence is a series of articles in which academics use research evidence to tackle the trickiest public policy questions.

Matt Field receives funding from the Medical Research Council, Economic and Social Research Council, Wellcome Trust, British Academy and Alcohol Research UK. He is affiliated with the UK Centre for Tobacco and Alcohol Studies.

This article was originally published at The Conversation. Read the original article.

Teenages making a toast in a pub. Photo: Getty

Matt Field is Professor of Experimental Addiction Research at the University of Liverpool.

Getty
Show Hide image

Autism and gut bacteria – the surprising link between the mind and the stomach

A recent paper has found that autistic-related social patterns can be reversed when one species of gut bacteria is present in the microbiome of mice. 

Autism – a developmental disorder that causes impediments to social interactions and behaviour – is usually linked by scientists to abnormalities in brain structure and function, caused by a mix of genetic and environmental factors. Scientists have almost always attempted to understand the way autistic people process the world around them by looking to the mind.

According to the National Autistic Society, “There is strong evidence to suggest that autism can be caused by a variety of physical factors, all of which affect brain development; it is not due to emotional deprivation or the way a person has been brought up.”

Recently, however, a lesser-known link to autism has gained traction. This time, the link is not found in the brain but in the gut.

Reporting their findings in the journal Cell, researchers from the Baylor College of Medicine, Texas, found that the presence of a single species of gut bacteria in mice could reverse many behavioural characteristics related to autism.

In the digestive tracts of humans and other animals, there exists a complex, symbiotically integrated network of trillions of microorganisms known as the “gut flora” or “microflora”. The idea that all these bacteria and microorganisms have taken up a home in our gut may initially seem startling, but they serve a number of beneficial purposes, such as aiding digestion and offering immunity from infection.

The potential link between gut flora and autism arose as researchers identified the increased risk of neurodevelopmental disorders, such as autism, among children born from mothers who were obese during pregnancy. The microflora of obese people is demonstrably different from those who are not obese, and as a result, connections have been made to the gut issues often reported in autistic people.

The senior author of the study and neuroscientist Mauro Costa-Mattioli said: “Other research groups are trying to use drugs or electrical brain stimulation as a way to reverse some of the behavioural symptoms associated with neurodevelopmental disorders – but here we have, perhaps, a new approach.”

To determine what the differences in gut bacteria were, the researchers fed 60 female mice a high-fat diet, with the aim of replicating the type of gut flora that would be found among people consuming a high-fat diet which would contribute to obesity. A control group of mice was fed a normal diet to serve as comparison. The mice in each group then mated, and their eventual offspring then spent three weeks with their mothers while being observed to see how behaviour and microflora was affected.

It was found that the offspring from the mice laden with high-fat foods exhibited social impairments, including very little engagement with peers. Meanwhile, a test called ribosomal RNA gene sequencing found that the offspring of the mice that were fed a high-fat diet housed a very different bacterial gut environment to the offspring of mice fed a normal diet.

Discussing the result, co-author Shelly Buffington was keen to stress just how significant the findings were: “By looking at the microbiome of an individual mouse we could predict whether its behaviour would be impaired.”

In an effort to understand whether the variation in microbiome was the reason for differences in social behaviour, the researchers paired up control group mice with high-fat diet mice. Peculiarly, mice eat each other’s faeces, which is why researchers kept them together for four weeks. The high-fat diet mice would eat the faeces of the normal mice and gain any microflora they held. Astonishingly, the high-fat diet mice showed improvements in behaviour and changes to the microbiome, hinting that there may be a species of bacteria making all the difference.

After careful examination using a technique called whole-genome shotgun sequencing, it was found that one type of bacteria – Lactobacillus reuteri – was far less prevalent in the offspring of high-fat diet mice than the offspring of normal-diet mice.

Discussing the method and finding, Buffington said: “We culture a strain of Lactobacillus reuteri originally isolated from human breast milk and introduced it into the water of the high-fat diet offspring. We found that treatment with this single bacterial strain was able to rescue their social behaviour.”

What the Lactobacillus reuteri seemed to be doing was increasing production of oxytocin, a hormone which is known by various other names such as the “trust hormone”, or the “love hormone”, because of its role in social interactions.

The results of the experiment showing that Lactobacillus reuteri can influence social behaviour are profound findings. Though the work would need to be transferred from mice studies to full human clinical trials to see if this could be applied to autistic people, the impact of adding Lactobacillus reuteri to the gut flora of mice can’t be underestimated. It seems then, for now, that research will go with the gut.