House of Mind

Cannabis is easily the most widely used illegal substance in the world. Although it still illegal at federal level, Washington and Colorado have legalized recreational cannabis use. Studies examining the relationship between marijuana use and neuropsychological function should be taken into consideration when making/reforming laws and  health policies.  I have received multiple questions regarding the effects of marijuana on memory and health and recently found a longitudinal study on this matter.

Prior evidence suggests that long-term, heavy cannabis use may cause enduring neuropsychological impairment beyond the period of acute intoxication (i.e. being high). Moreover, the magnitude and persistence of impairment depends on several factors including: quantity, frequency, duration and age of onset. Greater quantities, more frequent and earlier onset of use are associated with a poorer neuropsychological outcome. However, studies that compare pre-initiation neuropsychological functioning with longitudinal data on post-initiation functioning are scarce. 

Meier et. al investigated the association between persistent cannabis use  and neuropsychological functioning (assessed over a 20 year period) in over 1,000 individuals. Subjects received neuropsychological testing prior to onset of use (childhood; 1985-1986) and after some had developed a persistent pattern of use (~38 years old; 2010-2012). 

Important findings included: 

1. Subjects with more persistence cannabis dependence showed greater IQ decline. Those who never experienced cannabis experienced a slight increase in IQ. 
2. Subjects with more persistent cannabis dependence generally showed greater neuropsychological impairment across different areas of mental function: executive function, memory, processing speed, perceptual reasoning and verbal comprehension. The greatest impairments were in the domains of executive function and processing speed. 
3. Neuropsychological deficits induced by cannabis use were still significant  even when the researchers controlled for: past 24 hour cannabis use, past-week cannabis use, persistent tobacco, alcohol and/or hard drug dependence, and schizophrenia (all of which alternative explanations for poorer neuropsychological function). 
4. The effect of cannabis dependence on cognitive decline remained significant even after controlling for years of education. Persistent cannabis users with a high school education or less experienced greater IQ decline. 
5. Subjects who had an adolescent onset of use and were diagnosed with dependence prior to 18 years of age tended to become more persistent users. Importantly, adult-onset cannabis users did not appear to experience IQ decline as a function of cannabis use. 
6. Within-person IQ decline was apparent regardless of whether cannabis was used frequently or infrequently a year before testing. Thus, cessation of cannabis use did not restore neuropsychological functioning among adolescent-onset former persistent cannabis users. 

So it looks like persistent use of cannabis is particularly detrimental with adolescent onset. Some have speculated that this may be due to puberty, a critical period of brain development in which circuits related to decision-making, executive-function, and reward are undergoing reorganization/rewiring. Neurotransmitter systems like dopamine are also vulnerable during this period as they have not fully matured yet. Thus, the authors suggest that cannabis use exerts neurotoxic effects during this developmental period. 

However, one must remember that although the authors show compelling data, their data correlational and is not sufficient to establish causation. Furthermore, there is no mechanism underlying the negative impact of cannabis use on neuropsychological function- merely speculations (see above). It is also possible that there is another variable related to cannabis use and neuropsychological decline that the authors did not rule out. Another limitation of the study was the heavy reliance on self-reporting measures like self-reported frequency of use. Finally, it is hard to estimate dosages due to the variety of strains and potency of cannabis. 

I would personally suggest taking this information for what it’s worth. Neuroimaging studies in adolescents (humans) reveal structural and functional brain differences associated with cannabis use so we know that cannabis use changes the brain. I personally believe that cannabis use has negative effects on memory and general health, but I do not think that it’s as simple as the “Weed will make you stupid.” notion that some adults try to instill in adolescents.  After all, we already KNOW about the dangers and costs of alcohol/tobacco use and people still use them. For me, the key is to delay onset of use (if you must use) and to prevent adolescent use of cannabis. If you are a teenager with cannabis dependence, it is never to late to quit and try to remedy the effects.

Source:  (Click on the link for abstract)

Meier et. al. (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Science (PNAS). 109 (40): 2657-64. 

I was introduced to this concept last week while I was attending the funeral of someone who was thought to have experienced this during his last day alive. I visited the home where he passed away and was told that the nurses and family members were in awe of his passing because he had become “another person” during his last days of life. Some aspects of his memory seemed to have come back and he was more lively that he had been in awhile. I had never heard of such phenomena and decided to look into it. Below are some of the things I found. 

Terminal lucidity refers to the unexpected return of mental clarity and memory shortly before death in patients suffering from severe psychiatric and neurological disorders. This return of mental clarity usually occurs in the last minutes, hours of days before the patient’s death. Examples include case reports of patients suffering from tumors, strokes, meningitis, dementia or Alzeheimer’s disease, schizophrenia, and affective disorders. This is particularly striking considering that many of these disorders are caused by degeneration and degradation of the cerebral cortex, hippocampus, and other brain areas that are involved in memory and cognition processes. 

Several accounts suggest that during terminal lucidity, memory and cognitive abilities may function by neurologic processes that differ from those of the normal brain. So far the assumption is that the improvement of brain disorders or dysfunctions is caused by the altered brain physiology of the dying. There are two ways in which terminal lucidity is thought to exist: the severity of mental disturbance can improve slowly in conjuction with the decline of body vitality (typically schizophrenia cases) or full mental clarity may appear abruptly and unexpectedly shortly before death (more common in dementia cases). Although terminal lucidity has not been attributed to a specific medical cause, some authors have suggested that a high fever prior to dying might induce terminal lucidity.

Although terminal lucidity has been reported for around 250 years, it has received little medical attention because of its complexity and transience. Not to mention the ethical guidelines for the responsible conduct of research and the fact that these patients are  already mentally ill, making it even more difficult to include them in empirical studies. Academic interest in terminal lucidity declined after the mid-19th century. However, in 1975, Turetskaia and Romanenko published a detailed article concerning 3 cases of schizophrenic patients in a medical journal. According to Nahm and Greyson, this article is the only publication on terminal lucidity and mental disorders in medical journals throughout the 20th century. However, within the last few years interest in terminal lucidity in mental disorders has increased again due to recent case reports published by Brayne et. al (2008) and Grosso (2004) (see reviews below). 

The authors’ goal is to stimulate research on the pathophysiology of terminal states. For example, research on terminal lucidity could help elucidate the factors influencing the relationship between the mind and the brain, particularly as the brain deteriorates. Moreover, it could further understanding of memory and cognition processes and facilitate the development of new therapies aimed towards reversing the loss of memory and cognitive function in these patients. 

Sources: 

Nahm, M., Greyson, B., Kelly, EW., & Haraldsson, E.  (2012). Terminal Lucidity: A review and case collection. Archives of Gerontology and Geriatrics, 55:138–142.

Nahm, M., and Greyson, B. (2009). Terminal Lucidity in Patients With Chronic Schizophrenia and Dementia: A survey of the literature. Journal of Nervous and Mental Disease, 197 (12): 942-4.