Quick links from the past week in mind and brain news:
Previously it was known that higher IQ predicts longer life, but it was not known exactly why. A recent study suggests that faster reaction times, which are known to be linked to higher IQ, may be one of the key factors.
Recent research suggests that some aspects of visual function actually improve with age, particularly some motion perception skills (story 1, story 2).
The ability to make sense of ‘wholes’ rather than ‘parts’ (and vice versa) seems to rely on areas on the opposite sides of the brain in right and left handers.
An in-depth article from this month’s Scientific American on the neuroscience of memory is available online.
Bad news for smokers: Tobacco smoking can cause memory and cognitive impairment in adolescents, and smoking marijuana can have long-term effects on the brain’s blood flow.
A brain scanning study finds that when information is stored, activity in parts of the brain can predict whether it will be recalled accurately or form a false memory.
Mind Hacks 
The press releases for the marijuana say that permanent impairment was only observed in “heavy users,” which they defined as people who smoke more than *70* joints per week. The study isn’t published yet, so I haven’t been able to check up on this rather implausible number. But it’s not reasonable to say that marijuana permanently impairs cerebral blood flow, when their results suggest that there’s no impairment in someone who smokes, say, 50 joints per week — still an unbelievably large amount and far beyond what most regular users (or even abusers) consume.
The study of long term effects of marijuana you refer to has been refuted by a couple other sources.
I’ve uploaded the paper here:
Click to access mjstudy.pdf
It doesn’t seem to claim anything about permanent effects, as it only used a one-month measure.
The main findings are given as :
“The main findings of the study are that, in comparison to control subjects, marijuana users show 1) elevated systolic and mean blood flow velocity in the MCA [middle cerebral artery] and ACA [arterior communicating artery]; 2) higher PI [pulsatility index; measure of blood flow resistance] values in both the MCA and ACA; 3) no significant improvements in systolic velocity during a month of monitored abstinence; and 4) improvement in PI values only for the light and moderate marijuana users during the month of monitored abstinence. The present measurements, obtained during a month of observed abstinence from marijuana users, document potentially prolonged marijuana-mediated changes in vascular hemodynamics.”
The groups are defined like so:
“The light group smoked 11.0 +/- 3.5 joints per week (n = 11; range 2.2 to 15.0). The moderate group smoked the equivalent of 43.7 +/- 16.4 joints per week (n = 23; range 17 to 70). The heavy group smoked the equivalent of 130.8 +/- 73.0 joints per week (n = 20; range 78 to 350).”