Neuroscience research aims to understand neural structure and function, and how this relates to behavior, and normal physiological processes. The discipline is growing rapidly, with scientists publishing more articles. The improvement in technology and current trends in society generate various research topics and new techniques to compensate with society. Following steady decline, the prevalence of marijuana use “skyrocketed in the early and middle 1990s and has remained disturbingly high renewing concerns about it potentially deleterious effects on health” (O’leary et.al 2007, p.135). Cognitive abilities evolve during childhood and continue to refine throughout adolescence into late adulthood. In Seigel (2015), he states that during the adolescent years four qualities emerge: novelty seeking, social engagement, increased emotional intensity and creative exploration. Each has a positive and a negative aspect but plays a vital role in growing up. Novelty seeking can be described as a “increased drive for rewards in the circuits of the adolescent brain that creates inner motivation” (Seigel, 2015, p.7) The positive of novelty seeking is being open to change and explore the fascination of life, on the adverse taking risk for the sake of thrill can lead to dangerous behaviors. In light of drugs the outcomes can be addiction, dependency and ultimately a drastic effect on the human brain in various areas. Regular and prolonged exposure to marijuana, and or synthetic marijuana is associated with impaired cognition, attention, learning, episodic memory and sensory gating. Much debate surrounds the premises that cannabis symptoms resembles that of individuals suffering from schizophrenia. In memory test with prolonged use of marijuana short-term and long-term memory problems arise as a result in heavy chronic users.
As typical marijuana remains the “most commonly used illicit substance in the world” (Broyd et.al 2013, p.381) the drug is used by all ages primarily starting in adolescence. The adolescence brain goes through so many changes which includes apoptosis, the frontal lobe maturing into the largest lobe, which is responsible for voluntary movement, and the ability to project future consequences of actions. Cognitive functioning such as decision making matures last. Studies have hypothesized that cannabis use during early and middle adolescence might produce permanent or long-lasting change in neurocognitive functioning (Becker et.al 2010).
Becker et.al (2010), addresses the current issue that cannabis use during adolescent might interfere with regular brain development. Forty-three participants were broken up into two groups; early- onset users referred to as (EOU) (started smoking younger than 16) and late- onset users (LOU) (user that started smoking at 16 years of age or later). Subjects completed three verbal n-back task. Researchers described the purpose for using ‘n-back’ as “N-back task have been shown to reliably initiate working memory activation in healthy subjects and drug using populations” (p.838). Participants were asked to respond by button pressing when the target letter appeared on the screen, a total of twelve capital letters were used. In addition to memory being assessed verbal working memory, mental flexibility and motor speed were assessed as well.
Results from the study showed that early onset users had shorter abstinence period and use cannabis more frequently. The early use of cannabis might be associated with increased parietal, and frontal activity during working memory exercises. As mentioned earlier during adolescence the brain is changing due to pruning and forming new synapses to adjacent brain regions, early onset use of marijuana can interfere with this process. “Hyperactivity in the EOU was most pronounced in the left superior parietal lobe in the present study. This region has been proposed to be closely associated to focusing attention.” (p.843) Late onset users responded faster when compared to the early onset users during the task conditions.
O’ Leary et.al using attention task shows that smoking marijuana changes regional cerebral blood flow (rCBF). In five conditions twelve marijuana users were imaged using a PET scan after either smoking marijuana or a placebo. The five conditions consisted of a reaction time baseline task, two reaction time test one before and one after smoking marijuana or the placebo. Followed by two dichotic listening task in which one attended right ear and the other attended the left ear. Results from the study implicated that “large changes in rCBF include increases in extensive region of the ventral forebrain and the cerebellum and decreases in posterior visual areas of the brain” (O’ Leary et.al, 2007, p.141.) Other adjacent areas effected were orbital frontal cortex, anterior cingulate, temporal lobe and the insula.
Overall consummation of cannabis can have an impact on neuropsychological functioning later in life. With marijuana; the general population commonly recognizes tetrahydrocannabinol as (THC) and cannabidiol as (CBD). THC is the chemical that produces/causes the psychological effects related to a “high.” A high can affect one’s memory, pleasure, movements, and time perception. In the brain the overall increase of the dopamine level makes one feel happy in response to a pleasant experience. Having a regulated mood and emotional responses can emerge from drug usage. Rong et.al (2017) provided a review on data-driven support regarding the pharmacology and alleged clinical applications of CBD for treatment in individuals with anxiety, depression and sleep complaints. Researchers found among individuals with social anxiety disorder, CBD 400 mg significantly reduces anxiety. In the area of bipolar disorder and depression, CBD can be used as a mood stabilizer. Insomnia is the most common sleep disorder and is a known risk factor for multiple impairments leading to decreased quality of life. For areas of insomnia and other sleep related issues, “CBD administered at a dose of 160 mg/day significantly increased the quality of sleep” (Rong et.al 2017,p.215) however does come with mixed results for some individuals. Results from a recent meta-analysis indicated that cannabis was effective on improving sleep quality by eliminating the interrupting symptoms of pain. Chronic use of marijuana ultimately causes the user to become used to a certain amount. Inviting the need for greater use over time. The increased utilization of cannabis however is associated with worse overall sleep quality in the long-term.
With the growing use of marijuana, as a society we see the use of “synthetic” marijuana becoming adapted into society since 2010. Now almost illegal in all parts of the United States synthetic marijuana are human made by altering chemicals that are sprayed on plant material, so they can be smoked or sold as liquids to be vaporized and inhaled in e-cigarettes. These plants should not be consumed by individuals but have been known to produce the same “high” feeling as typical developed marijuana. Synthetic marijuana attaches to cannabinoid receptors in the brain especially areas in the frontal lobe and hippocampus. Two brands that has been talked about in general public are labeled as Spice and K2. The use of these products is increasing, and some of these products packages vary based on dosses. According to Vardakou, Pistos, & Spiliopoulou (2010), “different amounts or combinations of these substances seem to have been used in different “Spice” products to produce cannabis-like effects.” (p.158) Emergency departments are seeing patients who have smoked synthetic cannabinoids and exhibited symptoms that are not typical of marijuana. Such symptoms include; loss of consciousness, paranoid hallucinations, tremors and seizures. According to Camp (2011), “tolerance to these cannabinoids apparently develops rapidly and leads to dependency. Withdrawal is accompanied by profuse sweating, tremors, agitation, insomnia, headache, nausea, vomiting and diarrhea,” (p.292). Synthetic marijuana gives rise to another threat due to the premises it has no cure. Unfortunately, laboratory testing cannot detect synthetic marijuana within an individual body whether urination or blood testing like typical marijuana use.
Due to the intense research done on marijuana usage some researchers have reported marijuana related impairment to episodic memory in the brain meanwhile other have failed to observe such effects. Researchers Hart etl.al (2010) tested if acute marijuana smoking produces episodic and working memory disruption while using an electroencephalographic (EEG). They determined such an investigation will contribute to a better understanding of marijuana impact on neurophysiology and cognitive function.
Participants that were involved in the study smoked a single marijuana cigarette containing one of three concentrations (0%, 1.8%, 3.9%) and were asked to complete three tasks: a word presentation which consisted of working memory and word recognition. A list of 24 words were displayed and participants had to indicate the number of syllables contained in each word. After following, each person was given a recognition test of the words to test working memory again. For episodic memory participants were required to determine the spatial location of a dot on the word presented. Uniquely finding show that smoking “marijuana produces minimal effects on episodic and spatial working memory” (Hart et.al, 2010, p.337). Smoking marijuana did have effect an individual time perception. Participants needed more time to complete tasks when compared to the participants that did not smoke marijuana. 15- minutes after smoking marijuana a noticeable difference happened between the two groups. The marijuana group alpha waves decreased “before gradually increasing over the next three hours,” in hindsight marijuana use does alter individual overall attention. The placebo group EEG waves increased over the course of the day showing the task became easier and did not require much effort to perform the task.
Researchers Block et al. (2002), found different results from their study in addressing episodic memory. Chronic marijuana users performed memory test while using Positron Emission Tomography (PET) scan to measure brain blood flow. The memory test for this study focused on the encoding information into episodic memory and retrieval from episodic memory. Episodic memory is the remembering of events and experiences. Marijuana users for this study; were using marijuana “7+ times weekly on average” for two years. During the memory test subjects learned a list of 15 common words that were read to the subject and the subject had to recall as many words as he/she could. Only being reminded for the words that were missed off the list. After two consecutive trials researchers presented the words on a recording followed by a computer presentation. Following the computer presentation, a third period containing a new set of words were presented to the participants. Ultimately results from the study demonstrated “marijuana users performed more poorly than control subjects, they required more presentation, in learning and relearning” (Block et.al, 2002, p. 241). Researchers noticed marijuana users showed decreased memory in prefrontal activations. Marijuana users additionally relied on short-term memory instead of episodic memory encoding and retrieval.
Short term memory commonly referred to as working memory is concerned with immediate conscious perceptual processing. According to Ilan, Smith, & Gevin (2004), frontal lobes and cerebral cortex are “critical to sustained attention, working memory, and episodic memory function (p.214).” Researchers set out to see the effects of acute marijuana usage on demanding memory tasks to examine the neurophysiological and cognitive functions that rely specifically on brain areas where cannabinoid receptors are sufficient and such areas include the hippocampus. Short term memory also refers to the ability to control attention in an effort to retain and manage active situations in the face of distracting influences. Distracting influences can entail anything that interrupts one’s focus on a task. The study investigated the effects of marijuana smoking on EEG and event-related potentials (ERPs). Participants task involved three parts, which involved them responding by pressing one of two response keys on a box. The words displayed on the screen, tested word presentation, working memory, and word recognition. The list consisted of 20 words; half the words were presented in red and half in green. Subjects responded “red” or “green” to the display color of the words presented. Participants were instructed to remember each word and the color in which it was presented as well. In working memory aspect, a dot stimulus was displayed on each trial in which individual had to remember where the dot was placed. In the high load version of the task subjects had to remember the location of the dot on each trial and match the location of the dot two trials before.
Results demonstrated in the high load version of the working memory task, responses were slower and less accurate overall than in the low load version. “Marijuana intoxication appears to have interfered with subjects’ ability or will to keep their attention focused on performing the various repetitious tasks they were asked to do” (p.219).
In addressing an concurrent debates surrounding the symptoms of marijuana and schizophrenia, the pharmacologic effects of marijuana have been shown to exhibit paranoia, and hallucinations. These two symptoms are dominant in schizophrenia criteria. According to Broyd et.al (2013) “THC is the primary psychoactive constituent of cannabis and is linked with altered cognition and the induction of psychotic- like symptoms” (p.381) Nestoros et. al (2017), study was to examine if chronic cannabis user undergo these symptoms mentioned above. 48 individuals who were classified as heavy, chronic and solely cannabis users. For purpose of this study each individual had to be justified by the nine criteria of the Greek Republic for Drug Addiction. Drug abusers must meet at least three criteria out of the nine-criterion mentioned to be considered for the study. Example of criteria that must be fulfilled are “gives up or reduces important social, occupational or recreational pursuits due to the use of the substance,” “uses the substance very often in order to relieve or avoid withdrawal symptoms.” (Nestoros et al, 2017, p.336). Participants evaluation included Andreasen scale for Positive and Negative Symptoms Bender- Gestalt test, and Rey- Osterrieth complex figure test along with family history. Results showed “39.6% of the participants reported hallucination, 54.2% of the abusers reported delusions,” (Nestoros et. al 2017, p.337). Evidence from this study demonstrates that chronic heavy cannabis abuse can result in long lasting schizophrenia psychotic symptoms.
Filbey, et.al (2014), set out to characterize alteration in brain landscapes and determine the potential effects of chronic cannabis use. For participants to be considered for the chronic marijuana group various criterion had to be met; such as “no current or history of psychosis, brain injury, and had to regularly used marijuana at least four times a week over the last 6 months.” (p.16914) Three different MRI techniques were used to investigate a large group of chronic marijuana users compared to non-using groups; researchers took age and sex into factor. Researchers also set out to examine overall gray matter in marijuana users versus non-users and performed using an MRI machine. Second technique used, was a functional MRI scan to assess functional connectivity of the brain. The third technique used was a Diffusion Tensor Imaging (DTI) scan. DTI scan was used to provide an assessment of structural connectivity between brain regions via white matter.
To measure behavior related to marijuana use, Filbey, et.al used a (Marijuana Problem Survey)19-item marijuana questionnaire which assessed areas with negative outlook such as psychological, social, occupational and legal consequences. Examples of items on the scale consisted of “problems with family and significant others,” “missing work or losing a job.” Zero represented “no problem” and two represented a “serious problem.” (p.16915)
Results from the study showed that there is a decrease in gray matter in the orbitofrontal cortex in chronic marijuana users when compared to non-users. “Functional connectivity analysis revealed greater connectivity within the OFC network in marijuana users” (p.16917.)
As mentioned earlier dopamine in the brain responds to drug use, ultimately leading to the overall increase of the dopamine level. A study done by Volkow et. Al (2014) address the issue that dopamine is being decreased in marijuana abusers. Researchers used 48 participants that were taking methylphenidate. As mentioned earlier dopamine is a neurotransmitter that helps control the brain pleasure and reward systems. Researchers compared dopamine reactivity in healthy controls and marijuana users on a large sample. In using neuroimaging PET scan researchers provided a radiotracer to assess distribution volume in the striatum. To demonstrate the aspect of marijuana impact on the brain, the researchers compared marijuana users and a control group when challeneged with methyphenidate.
In distribution volume Volkow et.al noticed in the ventral striatum, there were an overall decrease with “negative emotionality and with marijuana craving such that the lower the response, the higher the negative emotionality and the craving” (p. E3154). This suggests that the weak responses might reflect reduced dopamine reactivity in marijuana abusers. Results of the study showed that marijuana users had lower dopamine responses, which has been shown to have an effect with the brain reward region and “marijuana abusers showed lower scores on positive emotionality and higher scores on negative emotionality than controls “(Volkow et. al 2014, p. E3155).
Great controversy surrounds marijuana due to the fact it is legal in 33 out of the 50 States. With marijuana becoming legal the arising concern is the long-term effects it can have on the brain psychologically. As stated, numerous times research has found that it can have impact on the adolescent brain and can ultimately lead to problem in the individual life years down the line. In summary heavy marijuana use can stop the brain from building the necessary connections to adjacent areas in the brain needed to function. Prolonged exposure to marijuana, and or synthetic marijuana depending on when first exposed can be associated with impaired cognition, attention, learning, episodic memory and sensory gating. In various cases schizophrenia like symptoms have been known to occur. Heavy use of marijuana can affect one’s short-term and long-term but regardless of all the impairment shown from research we as a society do not truly know the long-term effects of marijuana. “Heavy use” is difficult to define and a major limitation to past studies done. Major adversity surround marijuana such a; there are numerous ways to extract cannabis from the hemp plant, various strain contains different amount of THC which can determine how “high” one feels. The higher the dose of THC the longer you feel the sensation of being high. Future studies should focus on the longitude use of marijuana in a variety of career fields.