Barbella
Senator
I've long wondered what happened to make liberals as brain dead as they are. Finally, I KNOW!
.......Duke University psychologist Terrie Moffitt, PhD, and colleagues collected data from the Dunedin Multidisciplinary Health and Development Study, longitudinal research that has followed 1,000 New Zealanders born in 1972. Participants answered questions about marijuana use at 18, 21, 26, 32 and 38. They also underwent neuropsychological testing at ages 13 and 38.
The team found that persistent marijuana use was linked to a decline in IQ, even after the researchers controlled for educational differences. The most persistent users — those who reported using the drug in three or more waves of the study — experienced a drop in neuropsychological functioning equivalent to about six IQ points (PNAS, 2012). "That's in the same realm as what you'd see with lead exposure," says Weiss. "It's not a trifle."
There are some reasons to think that adolescents may be uniquely susceptible to lasting damage from marijuana use. At least until the early or mid-20s, "the brain is still under construction," says Staci Gruber, PhD, a neuroscientist and director of the Cognitive and Clinical Neuroimaging Core and the Marijuana Investigations for Neuroscientific Discovery (MIND) Program at McLean Hospital/Harvard Medical School. During this period of neurodevelopment, the brain is thought to be particularly sensitive to damage from drug exposure. And the frontal cortex — the region critical to planning, judgment, decision-making and personality — is one of the last areas to fully develop, Gruber says.
Also immature in teens is the endocannabinoid system. As its name implies, this system comprises the physiological mechanisms that respond to THC. That system is important for cognition, neurodevelopment, stress response and emotional control, and it helps to modulate other major neurotransmitter systems, says Krista Lisdahl, PhD, director of the Brain Imaging and Neuropsychology Laboratory at the University of Wisconsin, Milwaukee.
Repeated exposure to marijuana can dial down cellular activity in the endocannabinoid system. Such interference might be a bigger problem for immature brains, says Lisdahl. "That sets the stage for why adolescents may be more sensitive to the effects of repeated marijuana exposure, from a neuroscience perspective."
Altered brains
Indeed, a number of studies have found evidence of brain changes in teens and young adults who smoke marijuana. In 2013, Rocío Martín-Santos, MD, PhD, at the University of Barcelona, and colleagues reviewed 43 studies of chronic cannabis use and the brain. They found consistent evidence of both structural brain abnormalities and altered neural activity in marijuana users. Only eight of those studies focused on adolescents, but the findings from those studies suggested that both structural and functional brain changes emerge soon after adolescents start using the drug. Those changes may still be evident after a month of abstaining from the drug, the researchers reported (PLOS ONE, 2013).
Some of those brain abnormalities have been linked to cognitive differences. Gruber found that regular, heavy marijuana users — those who reported smoking five of the last seven days, and more than 2,500 times in their lives — had damage to their brains' white matter, which helps enable communication among neurons. Those white matter changes were correlated with higher impulsivity, she found, particularly in people who began smoking before age 16 (Psychopharmacology, 2013).
Much of Gruber's work compares heavy, regular marijuana users who began before and after age 16. Her results suggest there's greater risk in starting young. Compared with users who began after 16, early-onset smokers made twice as many mistakes on tests of executive function, which included planning, flexibility, abstract thinking and inhibition of inappropriate responses. As adults, those who started using before 16 reported smoking nearly 25 times per week, while those who started later smoked half as often, about 12 times per week. The early-onset smokers also reported smoking an average of nearly 15 grams each week, versus about 6 grams for their late-onset counterparts (Psychology of Addictive Behaviors, 2012).
Gruber's participants had reported using marijuana at least five times in the past week. But other labs have found structural differences in the brains of less frequent users. Jodi Gilman, PhD, at Massachusetts General Hospital/Harvard Center for Addiction Medicine, and colleagues used MRI to look for brain changes in 18- to 25-year-olds who smoked marijuana at least once per week, but were not dependent on the drug........
http://www.apa.org/monitor/2015/11/marijuana-brain.aspx
.......Duke University psychologist Terrie Moffitt, PhD, and colleagues collected data from the Dunedin Multidisciplinary Health and Development Study, longitudinal research that has followed 1,000 New Zealanders born in 1972. Participants answered questions about marijuana use at 18, 21, 26, 32 and 38. They also underwent neuropsychological testing at ages 13 and 38.
The team found that persistent marijuana use was linked to a decline in IQ, even after the researchers controlled for educational differences. The most persistent users — those who reported using the drug in three or more waves of the study — experienced a drop in neuropsychological functioning equivalent to about six IQ points (PNAS, 2012). "That's in the same realm as what you'd see with lead exposure," says Weiss. "It's not a trifle."
There are some reasons to think that adolescents may be uniquely susceptible to lasting damage from marijuana use. At least until the early or mid-20s, "the brain is still under construction," says Staci Gruber, PhD, a neuroscientist and director of the Cognitive and Clinical Neuroimaging Core and the Marijuana Investigations for Neuroscientific Discovery (MIND) Program at McLean Hospital/Harvard Medical School. During this period of neurodevelopment, the brain is thought to be particularly sensitive to damage from drug exposure. And the frontal cortex — the region critical to planning, judgment, decision-making and personality — is one of the last areas to fully develop, Gruber says.
Also immature in teens is the endocannabinoid system. As its name implies, this system comprises the physiological mechanisms that respond to THC. That system is important for cognition, neurodevelopment, stress response and emotional control, and it helps to modulate other major neurotransmitter systems, says Krista Lisdahl, PhD, director of the Brain Imaging and Neuropsychology Laboratory at the University of Wisconsin, Milwaukee.
Repeated exposure to marijuana can dial down cellular activity in the endocannabinoid system. Such interference might be a bigger problem for immature brains, says Lisdahl. "That sets the stage for why adolescents may be more sensitive to the effects of repeated marijuana exposure, from a neuroscience perspective."
Altered brains
Indeed, a number of studies have found evidence of brain changes in teens and young adults who smoke marijuana. In 2013, Rocío Martín-Santos, MD, PhD, at the University of Barcelona, and colleagues reviewed 43 studies of chronic cannabis use and the brain. They found consistent evidence of both structural brain abnormalities and altered neural activity in marijuana users. Only eight of those studies focused on adolescents, but the findings from those studies suggested that both structural and functional brain changes emerge soon after adolescents start using the drug. Those changes may still be evident after a month of abstaining from the drug, the researchers reported (PLOS ONE, 2013).
Some of those brain abnormalities have been linked to cognitive differences. Gruber found that regular, heavy marijuana users — those who reported smoking five of the last seven days, and more than 2,500 times in their lives — had damage to their brains' white matter, which helps enable communication among neurons. Those white matter changes were correlated with higher impulsivity, she found, particularly in people who began smoking before age 16 (Psychopharmacology, 2013).
Much of Gruber's work compares heavy, regular marijuana users who began before and after age 16. Her results suggest there's greater risk in starting young. Compared with users who began after 16, early-onset smokers made twice as many mistakes on tests of executive function, which included planning, flexibility, abstract thinking and inhibition of inappropriate responses. As adults, those who started using before 16 reported smoking nearly 25 times per week, while those who started later smoked half as often, about 12 times per week. The early-onset smokers also reported smoking an average of nearly 15 grams each week, versus about 6 grams for their late-onset counterparts (Psychology of Addictive Behaviors, 2012).
Gruber's participants had reported using marijuana at least five times in the past week. But other labs have found structural differences in the brains of less frequent users. Jodi Gilman, PhD, at Massachusetts General Hospital/Harvard Center for Addiction Medicine, and colleagues used MRI to look for brain changes in 18- to 25-year-olds who smoked marijuana at least once per week, but were not dependent on the drug........
http://www.apa.org/monitor/2015/11/marijuana-brain.aspx
