19 March 2010 by Jessica Hamzelou Being a teenager can be a drag. As if dealing with peer pressure and raging hormones weren't hard enough, your ability to learn new things is also reduced. Now the brain molecules behind this learning deficit have been identified in mice - and blocked. When children hit puberty, their ability to learn a second language drops, they find it harder to learn their way around a new location and they are worse at detecting errors in cognitive tests. Why is this? Sheryl Smith and her colleagues at the State University of New York now reckon that all of these behavioural changes could be due to a temporary increase in a chemical receptor that inhibits brain activity in an area responsible for learning. In 2007, Smith's team discovered that the number of these receptors soared in mice when they hit puberty, before falling back in adulthood. In their latest study, Smith's team set about finding out if these receptor changes in mice might lead to impaired learning abilities, rather like those seen in pubescent humans. The group examined the hippocampus – a region known to be involved in learning – in mouse brains. Sure enough, pubertal mice had seven times as many of the receptors as infant mice. In adulthood, the number of these receptors fell back to an intermediate level. The team was also able to examine individual neurons and could see that the extra receptors were being expressed specifically at "neural projections" – sites within the hippocampus known to be involved in learning. This was further evidence that the increase in receptors might affect learning. Finally, the group measured spatial learning abilities in the mice. The creatures were placed on a rotating platform, on which a stationary section delivered a mild electric shock. After a single shock, the infant mice learned to dodge the danger zone. The pubertal mice, however, failed to learn to avoid it even after several rounds. Smith reckons that the same mechanism might underlie the learning deficits teenagers experience. Cheryl Sisk at Michigan State University at East Lansing agrees that "mouse puberty is similar to human puberty, although the timescale is different". "The research adds to the growing body of literature indicating that puberty and adolescence are a unique period of nervous system development," says Sisk. "Adolescents aren't just in between children and adults. Their behaviour is different from both." In a further experiment, Smith found that she could remove the learning deficit by injecting pubertal mice with THP – a stress steroid. In children and adult humans, THP is naturally released in response to stress. It reduces brain activity and calms you down, says Smith. But in pubertal mice, THP has the opposite effect – increasing their stress. Smith suggests that in her most recent experiment, giving extra THP to pubertal mice similarly increased their brain activity and that this activity may have compensated for their learning deficits. If similar mechanisms underlie teenage learning deficits in humans, this result might point to ways to deal with them - either through behavioural changes or drugs. Smith suggests that a synthetic form of THP could be developed for teenagers with learning difficulties, although she acknowledges that care would need to be taken not to create any new problems. "We would have to be careful not to affect their mood," she says. Sisk cautions that it's too soon to apply the results to humans or to other types of learning outside the spatial type tested in the mice. Journal reference: Science, DOI: 10.1126/science.1184245Shocking memory
Learning restored
Thursday, August 19, 2010
Why teenagers find learning a drag
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