How Prenatal Exposure to Marijuana Affects Executive Functioning in Young Adults

Author:  Jennifer Charlicki

Institution:  University of Alberta



Every year, 211 million pregnancies occur around the world (WHO, 2007), and during pregnancy, one of the most commonly used drugs is marijuana (“Alcohol, drugs, and babies: Do you need to worry?” 2005). There has been an increase in the amount of pregnant women smoking marijuana to aid their morning sickness. However, marijuana use while pregnant has shown compensatory effects in how children prenatally exposed to marijuana perform tasks pertaining to executive functioning.

Past studies have found that prenatal exposure to marijuana impacts areas such as visual memory, attention, and impulsivity (Fried et al., 1992, 2003; Leech et al., 1999; Goldschmidt et al., 2000). More importantly, these studies have found that the effects persist into adulthood. These individuals who struggled with areas of working memory, where we retrieve, process, and manipulate information, found it hard to stay focused, and had difficulties with self-regulation. The overall findings from these studies have been that prenatal exposure to marijuana has a negative effect on our executive functioning, how we adapt to situations, plan, and work towards goals. These effects could potentially compromise a child’s likelihood of succeeding in areas such as school and work.

A 2016 study by Andrea Smith and colleagues from the University of Ottawa and Carleton University looked at the effects of prenatal exposure to marijuana on executive functioning, and how these effects endure into young adulthood. The study consisted of 31 individuals from ages 18 to 22 who were screened for current marijuana use during their pregnancy. Prenatal exposure was defined as at least one joint a week throughout the entire pregnancy. 16 of the participants had been prenatally exposed to marijuana, and 15 had not.

The participants underwent functional magnetic resonance imaging (fMRI) while performing four different tasks that required use of their executive functioning. The first task was Visuospatial 2-Back, where they saw a circle in 9 different positions on a screen, one at a time for 75ms. They had to press a button in the middle if the circle was presented in the middle, or press a button labeled “press for 2 back” if the circle was in the same position as the last 2 circles presented. The second task was Go/NoGo, where letters were presented in the middle of a screen one at a time for 75ms. Half of the letters presented were “x” and the other half were the remaining letters of the alphabet, where they had to either press a button that indicated a letter other than “x” had been presented, or a button that indicated that “x” had been presented. The third task was Letter 2-Back, where letters were presented in the middle of a screen for 1500ms, and they had to either press a button if the letter was in the same position as the last 2 letters, or press a button if an “x” was presented. The last task was Counting Stroop task, where they were shown common animal names (i.e. Dog), and then shown number stimulus words (i.e. One, two, three, etc.), and then had to press a button to indicate how many words had been presented. For example, they may have been shown “DOG DOG DOG DOG” for 1.5s, and they would press a button to indicate that 4 words had been shown, and then they would be shown “FIVE FIVE FIVE FIVE”, and they would have to press a button to indicate that 4 words had been presented.

The results found that performance on the tasks was similar across both groups, and performance was assessed based on reaction time and errors. Although the prenatal exposure group performed similarly, there was more neural activity in the posterior brain regions, which suggests that those who have been exposed compensate their responses by implementing more brain regions to perform a task. What this proposes is that although an individual prenatally exposed may perform similarly to someone who has not been prenatally exposed, they are having to use more brain regions to perform the same task. By exercising more areas of the brain for one task, they may be depleting their ability to perform other tasks because they have concentrated so much brain activity into one area. Therefore, though it may seem that the individuals in the two groups performed the same, their brain activity suggests that it took a lot more effort for those prenatally exposed.

The importance of these findings can help us further educate women on what exactly the risks are of marijuana use during pregnancy. Also, these findings may have the power to influence policies regarding marijuana use during pregnancy. It is important to understand what these actions mean in terms of a child’s future success and what their struggles may be. As said by Andrea Smith and her team, “these long term effects highlight the importance of optimizing the prenatal environment” (Smith, et al., 2016, p. 6) The goal is that with this knowledge, pregnancy environments can be improved in order to foster healthy outcomes for the child.



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