Pubdate: Tue, 11 Nov 2014
Source: Seattle Times (WA)
Copyright: 2014 The Seattle Times Company
Contact:  http://seattletimes.nwsource.com/
Details: http://www.mapinc.org/media/409
Author: Melissa Healy, Los Angeles Times

STUDY LOOKS AT POT USE AND BRAIN SIZE

Experimental mice have been telling us this for years, but 
pot-smoking humans didn't want to believe it could happen to them:

Compared with a person who never smoked marijuana, someone who uses 
marijuana regularly has, on average, less gray matter in his or her 
orbital frontal cortex, a region that is a key node in the brain's 
reward, motivation, decision-making and addictive-behaviors network.

More ambiguously, in regular pot smokers, that region is better 
connected than it is in nonusers.

The flow of signal traffic is speedier to other parts of that 
motivation and decision-making network, including across the 
superhighway of "white matter" that connects the brain's hemispheres.

The researchers who conducted the study speculate that the orbital 
frontal cortex's greater level of "connectedness" - which is 
especially pronounced in people who started smoking pot early in life 
- - may be the brain's way of compensating for the region's 
underperforming gray matter.

Whether these "complex neuroadaptive processes" reverse themselves 
when marijuana use stops is an important unanswered question, they added.

The new findings, reported Monday in the journal PNAS, confirm 
findings about chronic marijuana use from rodents.

But scientific evidence in humans has been more mixed.

Even now, however, the authors of the study acknowledge they cannot 
discern whether a pot smoker's smaller orbital frontal cortex is the 
cause or the result of chronic marijuana use.

A 2012 study found that subjects with a smaller orbital frontal 
cortex at age 12 were more likely to start using marijuana by age 16, 
suggesting that deficits in this crucial region may predispose one to 
substance-abuse behaviors.

This study, conducted by researchers from the University of Texas' 
Center for Brain Health and the Mind Research Network based in 
Albuquerque, N.M., did not follow subjects over time, so it is at a 
disadvantage in showing cause and effect.
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MAP posted-by: Jay Bergstrom