cannabisnews.com: Frequent Marijuana Use May Affect Brain Function 





Frequent Marijuana Use May Affect Brain Function 
Posted by FoM on April 03, 2000 at 08:41:12 PT
Upcoming Event - April 7th & 8th 2000 
Source: Science Daily Magazine
Recent University of Iowa Health Care studies indicate that some people who frequently use marijuana have substantially lower blood flow to certain parts of their brains; however, smoking the illicit drug does not affect brain size or structure. 
"Although marijuana is the most widely used illicit drug, surprisingly little attention has been given to the impact of frequent marijuana use on the structure or functioning of the human brain," said Robert I. Block, Ph.D., UI associate professor of anesthesia and lead investigator for the studies. "We wanted to examine these questions." The UI findings appear in separate articles in two recent issues of NeuroReport. "The question of whether marijuana use produces harmful effects is important because marijuana is the most popular illegal drug, and also because there is a lot of interest in its potential value as a medicine," Block said. "Many people believe that harmful effects have not been proven as clearly with marijuana as with most other illegal drugs. Our research showed some fairly dramatic changes in brain blood flow in some frequent marijuana users, even after the immediate effects of smoking had worn off." In one study, Block and his colleagues used positron emission tomography (PET) scanning techniques to determine whether frequent marijuana use affected brain function. They compared regional cerebral blood flow in 17 current, frequent young adult marijuana users with 12 comparable, control subjects who did not use marijuana. During the study, the subjects were lying quietly and did not perform any test and were not given any specific directions about what to think about. The marijuana users, who were using marijuana seven or more times weekly on average, were required to abstain from using the drug for at least 26 hours prior to the scan to eliminate short-term effects of marijuana smoking. The scan results showed that the marijuana users had up to 18 percent lower blood flow than controls in a large region--over a cubic inch of brain tissue--at the back of the brain, in the posterior cerebellum. There was very little effect of marijuana use anywhere else in the brain. Changes in brain blood flow usually correspond to changes in brain activity, so diminished blood flow indicates altered brain function in some frequent marijuana users. "The idea that frequent marijuana use impairs mental abilities is still controversial, but several recent studies, including our own, support such an association," Block said. "Although the cerebellum was traditionally thought mainly to be involved in controlling movements, more recent evidence has shown that it also plays a role in memory, attention, and other mental abilities. Some cognitive effects of marijuana use may be related to this lower activity of the posterior cerebellum." Block said that in past studies he and his colleagues have found changes in blood flow in several parts of the brain, including but not limited to the cerebellum, when frequent marijuana users perform memory and attention tests. "The most important next step would be to see if these changes in brain function persist for a long time after a person stops using marijuana," Block said. "We had our subjects stop for at least a day, to eliminate short-term effects of smoking. But itıs possible that some of the brain changes that we are seeing are withdrawal effects. If they go away after a few days of abstinence, they would be less serious than if they persist for weeks or months, or longer, after a person stops using marijuana." In the other study published in NeuroReport, Block and his colleagues wanted to establish what effects frequent marijuana use had on brain tissue volume and composition. The researchers, using magnetic resonance imaging (MRI), measured brain volume and composition of 18 frequent marijuana users and 13 non-using control subjects. Automated techniques were used to measure the volume of the brain as a whole and its major regions including, for most regions, separate measures of two major tissue types: gray matter and white matter. The marijuana users showed no evidence of overall or regional changes in volumes of brain tissue. "In the 1970's, a scientific paper was published describing cerebral atrophy in young marijuana users," Block said. "The paper was widely publicized and quoted for some time regarding the harmful effects of marijuana, but other researchers did not find any cerebral atrophy. Neuroimaging techniques have improved tremendously over the years, and we wanted to see whether these improved techniques would show decreases in brain tissue in any parts of the marijuana users' brains. We found no evidence of atrophy or any other harmful effects of frequent marijuana use on brain structure." Although the study did not show any harmful effects, "these findings donıt give marijuana a clean bill of health," Block said. "Anatomical abnormalities might occur at a microscopic level that cannot be detected by MRI, and MRI abnormalities might be observed in individuals who used marijuana for longer periods than the people we studied." On average, the marijuana users in the test had used the drug for about four years. Block, who has led a number of marijuana investigations, will be one of the speakers at a conference titled "Medical Marijuana: Science-Based Clinical Applications." The conference, to be held April 6-8 at the UI, is the first national conference to educate health care professional and researchers on the therapeutics of marijuana. A conference brochure containing a full list of speakers and panels, as well as a registration form, can be obtained at the Web site: http://www.drugsense.org/ncct or by calling the UI Center for Conferences and Institutes at 800-551-9029 or 319- 335-4141. Editor's Note: The original news release can be found at: http://www.uiowa.edu/%7Eournews/current/News/2000/mar00/hea/0329marijuana.html Note: This story has been adapted from a news release issued by University Of Iowa for journalists and other members of the public. If you wish to quote from any part of this story, please credit University Of Iowa as the original source. You may also wish to include the following link in any citation: http://www.sciencedaily.com/releases/2000/03/000331090541.htmUniversity of Iowahttp://www.uiowa.edu/Iowa City, Iowa Date: Posted April 3, 2000 Copyright İ 1995-2000 ScienceDaily MagazineEmail: editor sciencedaily.com Related Article:National Conference on Cannabis Therapeutics http://www.cannabisnews.com/news/thread5268.shtmlSeminar Examines Medical Marijuanahttp://www.cannabisnews.com/news/thread4912.shtmlCannabisNews Articles On Patients Out of Timehttp://www.google.com/search?num=10&q=cannabisnews+patients+out+site:www.cannabisnews.com
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Comment #4 posted by FoM on April 05, 2000 at 08:38:53 PT
Thanks observer
Hi observer! Good comment and I like how you were able to highlight some of your post. Thanks for posting your comments at Cannabis News. They are always very enlightening. I really appreciate it!
Drug Policy Talk
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Comment #3 posted by observer on April 04, 2000 at 20:21:56 PT
Doc Block's Axe Grind
> During the study, the subjects were lying quietly and did not perform any test and were not given any specific directions about what to think about. The marijuana users, who were using marijuana seven or more times weekly on average, were required to abstain from using the drug for at least 26 hours prior to the scan to eliminate short-term effects of marijuana smoking. . . . The scan results showed that the marijuana users had up to 18 percent lower blood flow than controls in a large region--over a cubic inch of brain tissue--at the back of the brain, in the posterior cerebellum.Read that again ... "the subjects were lying quietly and did not perform any test and were not given any specific directions about what to think about."In other words, they were all told to lie quietly...Would not such a test indicate that the cannabis users in fact complied more fully with the instructions to lie quietly then the non-users? Maybe users are able to able to slip into a relaxed (or alpha) state nore easily? (Or should we say, more accurately, after a day of not smoking, this one small part of the brain was, for some users, able to become a whopping 18% less active than non-users?) This study doesn't tell us anything about that.The prejudice of the whole setup is such that any difference in transient activity will be interpreted as negative or "harmful". The author of this piece was clever enough to not explicitly interpret the ostensible differences measured as such ... except in one place, and even there covering his backside by quoting a researcher. The researcher, in turn, tries to cover his hind end by not coming out and saying that the differences measured are harmful, per se, but note how cleverly he uses the propaganda technique of insinuation to slyly hint that the alleged changes he claims to have measured are indeed "harmful effects" --Block: "Many people believe that harmful effects have not been proven as clearly with marijuana as with most other illegal drugs. Our research showed some fairly dramatic changes in brain blood flow in some frequent marijuana users, even after the immediate effects of smoking had worn off." Note he stays just this side of coming out and saying that these supposed effects are harmful effects: yet only just so. The technique of insinuation is obvious. (Block already knows that marijuana is "harmful", and Block marshals the forces of Science for us to prove it!)Again, keep in mind that these "changes" could be the result of superior performance of the cannabis users: they are told to lie quietly, and so they do it. Of course, their superior compliance on this test too, would be more `evidence' of "harmful effects". Cannabis users are scapegoats: any excuse will do to heap more blame upon them.I also suugest that the controls are flawed for this expiriment, also. For example, what happens when people who "frequently" watch movies and TV are deprived of them for 26 hours and measured? In a society were using cannabis is illegal, is the huge expirimental base of "17 current, frequent young adult marijuana users" representative of all users? Also, just how many had this "change"? "some people who frequently use marijuana have ...""in some frequent marijuana users""the marijuana users had up to 18 percent lower blood flow than controls""Some"? Well, was it all 17 of the users? Most of them? Two? Just one? They don't tell us.Yes, they just forgot to tell us that too. I bet if it were all or most or even a significant percentage of the users that had this "change" (thus enhancing the on-message spin-ability of this little study), then we could certainly hear about it. But we didn't.I also note, in passing, that the whole reason people ever use marijuana or any mind-altering substance is precisely to affect brain function.
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Comment #2 posted by cerebus on April 04, 2000 at 00:16:46 PT
also
women that show aptitue for math and other brain activities i believe also use a substantially less amount of blood flow to occompish tasks than women who had average math aptitudes who expended much more blood flow and mental power to solve the same tasks that the other women used less. if anything this study only merits further study but no conclusions as of yet.
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Comment #1 posted by MMMM on April 03, 2000 at 22:23:55 PT
Blood flow
It's also been noted that people with high IQ have a lower blood flow to the brain when solving problems than people of lower IQ. Did the researchers adjust for the IQ variable? I think not. 
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