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Recreational adolescent use of marijuana can result in adult cognitive problems including learning, thinking, and memory problems (Crean, Crane, & Mason, 2011). Marijuana, also known as cannabis, is known to humanity for thousands of years. It is obtained from the hemp plant, known as Cannabis sativa. Marijuana is one of the most popular, easily obtained drugs, and controversial drugs. It contains psychoactive chemicals such as delta-9-tetrahydrocannabinol, which was obtained in the mid-1960s. This is the key chemical behind the development of controversies in this and the last century. Certain others aspects of the endocannabinoid system including cannabinoid receptors such as CB1 (cannabinoid receptor type 1) as well as CB2 (cannabinoid receptor type 2), and other important endogenous cannabinoids as, for example, anandamide and 2-arachidonoyl glycerol were recognized over two decades later. Although phytocannabinoids are found to be related to the improvement of certain health conditions, but frequent use of marijuana can result in increased chances of adverse events, thereby resulting in health problems. Several laws have been developed in different parts of the world to control the production and use of the drug. In the United States (U. S.), marijuana (cannabis) has been prohibited since the 1937 Marijuana Tax Act. The drug has been classified as an illegal Schedule I drug by the US Drug Enforcement Agency (DEA). However, some states of the U.S. have made it legal to have small amounts of cannabis (Greydanus, Hawver, Greydanus, & Merrick, 2013). Marijuana is used by people medically, recreationally, and spiritually. Although the drug is controversial and considered illegal, but it is one of the most widely used recreational drugs in the U.S. Difference between the medical and recreational use develops on the basis of the use of drugs. Moreover, the amount of drug and purpose of ingestion are also different in the medical and recreational use of drugs. Recreational use of the drug refers to the frequent use of the drug to get pleasing sensations and to feel relaxed as well as to decrease the self-conscious without getting the addictive risks of opioids or stimulants. After the administration of drug into the body, especially its inhalation, many users feel euphoria and perceptual alterations such as time distortion and increased intensity of ordinary experiences including watching films, eating food, and listening to music. According to the reports of the United Nations, about 190 million people used cannabis in the year 2007, and that was illicit recreational use of the drug (Bostwick, 2012). It is commonly used by adolescents and young adults. Adults are those, who have reached their sexual maturity. Adulthood starts with puberty, but now, the term adolescence is more commonly used for people, who have reached their puberty. Adolescents are the people in the age range of 14 to 20 years. Young adults are usually considered as the people in the age range of 20 to 27 years (Jacobus & Tapert, 2014). This essay will explore that adolescent recreational use of marijuana does lead to adult memory deficits as found through the changes in shapes of brain parts.
Marijuana use and the acute administration of its psychoactive constituents such as delta-9-tetrahydrocannabinol (Δ9-THC) can result in disturbances in episodic memory by disrupting the activity of CB1 in hippocampus (Smith et al., 2015). Smith et al. worked on the effect of cannabis use on the hippocampal shape or volume and hippocampus morphology, and the affect of the changes in hippocampus as a result cannabis use on episodic memory deficit. They also examined the differences between the morphology of hippocampus of healthy people and patients of schizophrenia (2015).
In order to know the differences, they compared the hippocampus of the people without any history of cannabis use to the people with a history of cannabis use. Researchers worked on 44 healthy controls with no history of cannabis use, 10 healthy controls with a history of cannabis use, 28 schizophrenia subjects with no history of cannabis use, and 15 schizophrenia subjects with a history of cannabis use. A total of 97 subjects took part in the study. This approach helps the researchers in a 2 x 2 assessment of combined illness-associated and cannabis associated episodic memory deficits. Subjects were also considered on the basis of age, gender, and parental socioeconomic status. Mean age of the participants at the time of the study was in the range of 25 years to 27 years, i.e. they were young adults, who have either used cannabis in their adolescence, i.e. during 16 or 17 years of age, or not used the drug in their adolescence. None of the participants of the study have used any other drugs, and almost all of them were not using marijuana for about two years at the time of the study (Smith et al., 2015).
In order to know about the memory performance of the participants of the study, researchers asked participants to listen to several one-minute stories. After listening to the stories, participants were asked to retell the stories after 20-30 minutes with as much information in the stories as possible. This test was used to check the ability to store, recall, and encode details from the stories (Smith et al., 2015).
Researchers performed magnetic resonance imaging (MRI) for brain mapping and producing surface-based representations of the hippocampus of all the subjects in four different groups. Surface maps of the hippocampus were developed to know about the morphological differences. Hippocampal volume was obtained from the space within the surface, and shape was assessed from the alignment of the part with the previously established template surface. This brain mapping helped the researchers in knowing a relation between the episodic memory and the past cannabis use. In order to analyze the obtained data, researchers performed analysis of variance (ANOVA) (Smith et al., 2015).
Researchers found that the surface features of the hippocampus were different in people with a history of cannabis use. Both normal and schizophrenic subjects showed cannabis-related hippocampal shape differences and deficits in episodic memory performance. Research shows that normal people with the previous history of cannabis use scored lower in episodic memory test as compared to normal people without the previous history cannabis use. Similarly, schizophrenic patients with a history of cannabis use scored lower than schizophrenic patients without a history of cannabis use. Moreover, schizophrenic patients scored lower than the normal participants having a history of cannabis use. Researchers noted that the participants, who had used marijuana heavily during adolescence, have about 18% lower performance in memory tasks as compared to the participants, who had not used marijuana. In the study, prolonged use of cannabis in people with a history of cannabis use relates with the “cannabis-like” shape in different hemispheres of the brain. It is reported that more “cannabis-like” shape in the left hemisphere of normal people with and without a history of cannabis use correlates with poorer episodic memory. Researchers noted that prolonged use of cannabis correlated with “cannabis-like” shape in the right hemisphere in both normal people with a history of cannabis use and schizophrenic patients with a history of cannabis use. In case of normal people with a history of cannabis use, researchers reported that statistical significance was not obtained in prolonged used of cannabis and “cannabis-like” shape in the right hemisphere. On the other hand, larger duration of abstinence from cannabis use was related to a decreased “cannabis-like” shape in the left hemisphere (Smith et al., 2015).
In the study, researchers have reported various results that were either statistically significant or not significant. Significance of the between-group differences was determined by ANOVA. It has been found that both schizophrenia patients and normal people without a history of cannabis use showed significant verbal IQ-by-PC interaction. Here, PC shows principal components on the aligned right and left surfaces showing variations in the shape. Researchers have also reported that episodic memory showed significant variations in all of the four groups, i.e. people in different groups have different memory (Smith et al., 2015).
One of the strengths of the study is that researchers performed a very detailed analysis of the changes in the hippocampus of the normal people with and without a history of cannabis use and schizophrenic patients with and without a history of cannabis use. They have not only used MRI but also performed a thorough statistical analysis on the collected information. On the other hand, an important limitation of the study is that it was unable to show a causal relationship between the past history of cannabis use and chronically disturbed episodic memory. Moreover, the number of sample was not sufficiently large in the study. On a further note, researchers collected the information about history of cannabis use from the participants that could result in biased reports (Smith et al., 2015).
In this study, researchers reported both inward as well as outward shape differences in the hippocampus as a result of cannabis use in the past (Smith et al., 2015), and the same thing was reported by other researchers (Solowij et al., 2013). In this study, researchers found a general trend that right hippocampal volume is greater than left hippocampal volume, which is also found in other studies (PEDRAZA, BOWERS, & GILMORE, 2004; Woolard & Heckers, 2012). The observed hippocampal shape of schizophrenic patients found in this study is also consistent with other studies (Johnson et al., 2013; Qiu, Gan, Wang, & Sim, 2013).
Conclusively, this research shows that a history of cannabis use in adolescents can result in differences in the hippocampal morphology and can also lead to impairments in the episodic memory. This study shows that it is better to stop using marijuana as early as possible because the strong and long-term use of marijuana has stronger relation to abnormalities in the brain, thereby leading to memory problems. Moreover, better policies have to be developed for marijuana use in adolescence. Considering this study, it can be found that a longitudinal study is required to confirm the relationship between marijuana use in the adolescence and hippocampus abnormalities and memory deficits.
References
Bostwick, J. M. (2012). Blurred boundaries: the therapeutics and politics of medical marijuana. Paper presented at the Mayo Clinic Proceedings.
Crean, R. D., Crane, N. A., & Mason, B. J. (2011). An evidence based review of acute and long-term effects of cannabis use on executive cognitive functions. Journal of addiction medicine, 5(1), 1.
Greydanus, D. E., Hawver, E. K., Greydanus, M. M., & Merrick, J. (2013). Marijuana: current concepts. Front Public Health, 1.
Jacobus, J., & Tapert, S. F. (2014). Effects of cannabis on the adolescent brain. Current pharmaceutical design, 20(13), 2186.
Johnson, S. L., Wang, L., Alpert, K. I., Greenstein, D., Clasen, L., Lalonde, F., . . . Gogtay, N. (2013). Hippocampal shape abnormalities of patients with childhood-onset schizophrenia and their unaffected siblings. Journal of the American Academy of Child & Adolescent Psychiatry, 52(5), 527-536. e522.
PEDRAZA, O., BOWERS, D., & GILMORE, R. (2004). Asymmetry of the hippocampus and amygdala in MRI volumetric measurements of normal adults. Journal of the International Neuropsychological Society, 10(05), 664-678.
Qiu, A., Gan, S., Wang, Y., & Sim, K. (2013). Amygdala–hippocampal shape and cortical thickness abnormalities in first-episode schizophrenia and mania. Psychological medicine, 43(07), 1353-1363.
Smith, M. J., Cobia, D. J., Reilly, J. L., Gilman, J. M., Roberts, A. G., Alpert, K. I., . . . Csernansky, J. G. (2015). Cannabis‐related episodic memory deficits and hippocampal morphological differences in healthy individuals and schizophrenia subjects. Hippocampus, 25(9), 1042-1051.
Solowij, N., Walterfang, M., Lubman, D. I., Whittle, S., Lorenzetti, V., Styner, M., . . . Yücel, M. (2013). Alteration to hippocampal shape in cannabis users with and without schizophrenia. Schizophrenia research, 143(1), 179-184.
Woolard, A. A., & Heckers, S. (2012). Anatomical and functional correlates of human hippocampal volume asymmetry. Psychiatry Research: Neuroimaging, 201(1), 48-53.
