Martine Skumlien has just completed a PhD looking at the association between cannabis use and reward processing, and the role of adolescent vulnerability
Research group: Barbara Sahakian
Supervisor: Barbara Sahakian
Advisor: Christelle Langley, Will Lawn, Valerie Voon
Can you give us a short background into what your PhD/MPhil was about?
Cannabis is the third most commonly used controlled substance worldwide, after alcohol and nicotine. With the legal profile of cannabis currently changing in many countries, a better understanding of how it affects the brain and cognition is urgently needed. Cannabis use has historically been linked with amotivation, and cannabis users are regularly depicted in the media as lazy and demotivated. From a psychological perspective, this would imply that cannabis use interferes with reward processing – processes underpinning reward seeking and consuming rewards. There are other reasons to believe this as well. For instance, many theories of addiction emphasise heightened sensitivity to drug rewards and reduced sensitivity to non-drug rewards as central to the development of substance use disorders. However, it remains unclear whether cannabis use is associated with disrupted reward processing or whether the stereotypes we see in movies, TV and public safety adverts are based on incorrect assumptions about how cannabis affects the brain.
Furthermore, cannabis use typically starts in adolescence and is disproportionately prevalent among adolescents and young adults. Adolescence is an important period of socio-emotional, cognitive, and neural development, and the experiences we have during this time can have a profound and lifelong impact. As adolescent neuromaturation is experience-driven, many researchers believe that the adolescent brain may be particularly vulnerable to the potentially harmful effects of cannabis. Yet, most previous studies have included only adult cannabis users, and none have compared adult and adolescent cannabis users directly with age-matched controls.
The aims of this thesis were twofold. First, we investigated whether acute and chronic cannabis exposure was associated with disrupted reward processing across psychological, behavioural, and neuroimaging outcomes. Second, we assessed whether adolescents showed stronger reward processing disruption after acute or chronic cannabis exposure than adults.
How would you sum up your main findings?
Most of my PhD research comes from the UCL ‘CannTeen’ project, which is a large MRC-funded study investigating whether adolescents and adults respond differently to acute and chronic cannabis exposure. We looked at reward processing using many different methods, including responses to reward cues and outcomes in the brain during fMRI, willingness to expend physical effort for reward on a behavioural task, subjective ‘wanting’ and ‘liking’ of real rewards, and questionnaire measures of anhedonia and apathy. We found that acute cannabis attenuated responses to monetary reward cues in key reward regions in the brain relative to placebo – that is, our participants showed less reward-related brain activity when anticipating winning money while they were ‘high’. However, there were no differences between regular cannabis users (who used cannabis on average ~3 days per week) and controls on any neural, behavioural, or psychological measure of reward processing.
When we looked at adolescent and adult cannabis users separately, we found that adolescent users had greater levels of anhedonia – lack of interest in or pleasure from previously rewarding activities – compared with adolescent controls. In contrast, adult users had lower levels of anhedonia than adult controls. There was no evidence of adolescent vulnerability or resilience to cannabis-related differences in any of the reward-processing outcomes we assessed. This research shows that reward processes appear to be largely spared in adolescents and adults with moderate cannabis use and that the cannabis-related ‘amotivational syndrome’ is not supported by scientific evidence.
All five of my PhD studies have been published in peer-reviewed scientific journals, including Neuropsychopharmacology and Neuroscience & Biobehavioral Reviews.
What made you want to do a PhD?
I knew I wanted to do a PhD from my first term as an undergraduate student in psychology at the University of Oslo. I never considered any other options – nothing else seemed as exciting, challenging, or meaningful as being a scientific researcher. I caught another lucky break during my MRes in cognitive neuroscience at UCL, where I got to do my master’s research on the CannTeen study. This lit my passion for cannabis research, and I was fortunate enough to be able to continue working on this brilliant project for my PhD.
One thing I know for sure is that I would never have made it to my PhD had it not been for all the incredible researchers who invested in me early on, during my time as an undergraduate and graduate student and as a research assistant. I owe them a great deal of gratitude.
What was your best day during your PhD?
I had many brilliant days during my PhD and it’s hard to pick just one. Those that spring immediately to mind include the day I returned to the office after the first round of COVID lockdowns and the first time I presented my work to a public audience. Another immensely rewarding experience was seeing a widening participation summer programme (‘Summer CAMP’: https://www.psychiatry.cam.ac.uk/students/summer-camp/) I had participated in developing and running, together with other students at my department come to fruition. I have rarely felt so proud as on the final day when the undergraduate students who had completed the programme were all together (albeit on Zoom) to present the work they had done. Finally, as boring and cliché as it sounds, the day my first PhD paper was accepted was an important high point. For many of us, the PhD comes with a lot of self-doubt and feelings that we are not good enough or don’t deserve to be where we are. Having my first PhD paper published served as a reminder that my work was good enough and that I was actually capable of doing the PhD!
What was your worst day during your PhD?
Similarly cliché, my first PhD paper rejection was rough. As the gods of fate would have it, this coincided with a particularly dark and grey November weekend at the start of the second dejecting round of COVID lockdowns in the UK. As such, my level of resilience was already quite low. I did everything you are not supposed to do when you get rejected – I took it personally, as a true reflection of my overall capabilities as a researcher, and as proof that I was not cut out to do a PhD. I was afraid of telling anyone as I thought they, too, would think I was a failure, and therefore kept the rejection to myself for several days. However, when I finally did tell my supervisor and collaborators, quite the opposite happened – they were all incredibly kind and supportive. They shared some of their own stories of rejection and academic failures. My negative feelings vanished immediately. In retrospect, this experience gave me two important lessons that helped me a lot for the rest of my PhD. First, it is important to share it with others if you are struggling – a truism many of us tend to forget. Second, rejections are part of the game and (for most) far outnumber the successes. Fortunately, I have developed thicker skin since then!
Do you have any words of advice to future PhD/MPhil students in Psychiatry?
‘Imposter’ feelings are almost ubiquitous and in no way reflect your intelligence and capabilities. The most high-achieving people often seem to be plagued by self-doubt. It helps to share these feelings with others, especially with other PhD students. My strongest advice would therefore be to try and create a support network of other PhD students, even if they are not in your department or your university. More importantly, use this network if you are struggling. Doing a PhD brings about some pretty unique challenges, and I have found that the best way of handling these is by sharing them with other people who can relate to what I am going through.
What do you hope to do next?
I want to stay in academia for the time being and am currently planning the next step of my career post-PhD. Regardless of where I end up, I want to continue researching to improve the lives of people who use cannabis and other drugs.