We have all heard the trope of the 'lazy stoner'1. It has permeated modern, Western society to the extent where 'stoners' have come to embrace—or perhaps simply accept—it themselves. But, is this view backed up by science? That was the question Martine Skumlien2 set out to address in her talk last December, the first one in a series dedicated to bringing you drug science by young researchers. This article summarises her presentation and goes over some of the salient points that it entailed.
As a doctoral student at the University of Cambridge, Martine investigates the effects of cannabis use on the brain and cognition, with an especial focus on adolescents. Cannabis is the third most widely used recreational drug in the world, a fact Martine contrasted with the relatively scarce research on some of its effects, such as on reward processing. With the recent push to legalise or decriminalise cannabis in many parts of the world, the time is ripe for a better understanding into how it affects the brain. There are many misconceptions surrounding its use and the stigmatising ones can often have far-reaching, harmful consequences. Martine’s research is pertinent for clearing this smoke.
To get a lay of the land, Martine, first, had to see what science had to say about the link between cannabis use and a lack of motivation. The latter can encompass several different things: do cannabis users find things uninteresting, does cannabis make things unpleasurable, is the motivation to learn weakened, or are users driven by different—perhaps greater—rewards? She and her colleagues went through available literature 3, finding a nebulous picture with results differing based on the methodology used or the sub-process probed: results were somewhat supportive of a link in domains such as anhedonia while performance on behavioural motivation tasks did not seem to be affected by cannabis use. Where there is evidence of altered reward cognition related to cannabis use, its precise nature and the directionality of the link remain hazy. Furthermore, most research has thus far been conducted to investigate the negative effects of cannabis use. As Martine stated, if one sets out to look for a specific thing what else will they find if not that?
To address these issues, Martine's research focuses on determining whether cannabis-use leads to altered reward processing, and if so what processes underlie this change. It also aims to find out whether adolescents are more vulnerable to such alterations; not only are they likely more vulnerable to drug use in general, but they are quite underrepresented in the existing research.
Martine’s PhD is still ongoing, but she has already tested the experimental waters on the subject using the pandemic as a backdrop. Her study investigating change in the effects of cannabis use before and after the first lockdown in the UK found an increase in apathy and anhedonia in all participants regardless of the user’s status during the lockdown4. An important takeaway was the increase being significantly greater in teens and those who were classified as dependents. What this study wasn't able to probe, however, were the processes underlying these alterations.
Through collaboration with the UCL Clinical Psychopharmacology Unit5, Martine tests her subjects using tasks that vary the effort required to perform them and the reward gained upon completion. Participants take part in activities such as the Monetary Incentive Delay (MID) task while researchers scan their brains using functional magnetic resonance imaging (fMRI). Experiments are conducted at least 12 hours after instances of cannabis use to minimise any residual effects. There are, of course, caveats to such an approach. When we consume cannabis it isn't in a lab nor under an fMRI, and it is unlikely anyone is instructing us to perform experimental tasks. But, what it may lack in ecological validity, it makes up for with precision. Confounding factors such as nicotine use and depression can obscure the mechanisms underlying any cognitive alterations, and make it harder to establish causal direction for any correlations found; these factors can be measured and controlled for in the lab.
So, while she waits for her research to conclude, what does Martine think of the link between cannabis and motivation? While research on reward processing overall is inconclusive, it is becoming clear that using cannabis is unlikely to cause a lack of motivation non-acutely, thus making it difficult to carry on using the trope of the slothful cannabis user. Not only does it rest on a shaky foundation, its stigmatising nature leads to real-world consequences which are rarely positive. Yes, there does seem to be some indication of an altered cognition related to cannabis use, but its precise nature needs to be investigated. Martine is doing just that.
References
1 aa4398743873 (2015). Stoner Sloth Compilation. YouTube. Accessed: 10 April 2022.
2 Cambridge Neuroscience (2022). Ms Martine Skumlien. University of Cambridge. Accessed: 10 April 2022.
3 Skumlien, M., Langley, C., Lawn, W., Voon, V., Curran, H. V., Roiser, J. P., & Sahakian, B. J. (2021). The acute and non-acute effects of cannabis on reward processing: A systematic review. Neuroscience & Biobehavioral Reviews, 130, 512-528.
4 Skumlien, M., Langley, C., Lawn, W., Voon, V., & Sahakian, B. J. (2021). Apathy and anhedonia in adult and adolescent cannabis users and controls before and during the COVID-19 pandemic lockdown. International Journal of Neuropsychopharmacology, 24(11), 859-866.
5 Clinical Psychopharmacology Unit (2022). CannTeen. Univeristy College London. Accessed: 10 April 2022.
