This week's issue really is chock full of goodies. The rest I'll summarize in brief.

China may get fusion power to work first.

The world's first fully superconducting tokamak is soon to produce a discharge of ionized gas or plasma.

If all goes as planned, China's Experimental Advanced Superconducting Tokamak (EAST) project will make its first plasma in the next few weeks.

EAST uses superconducting coils to create a magnetic field that confines plasma inside a doughnut-shaped vessel known as a tokamak. The behaviour of the plasma should shed light on the potential of nuclear fusion as an energy source.

Conventional experimental fusion machines use copper coils, or a combination of copper and superconducting coils, to trap the hot plasma. But copper coils heat up and need to be cooled down regularly, thus limiting operating time. EAST has only superconducting coils so it can be operated continuously.

The mechanism for the detection of sour tastes has been explained, but also of interest in this article is this first sentence from the abstract.

Mammals taste many compounds yet use a sensory palette consisting of only five basic taste modalities: sweet, bitter, sour, salty and umami

Umami? I'm not the only one who would be confused, hence in the same sentence they explain it is the taste of monosodium glutamate or MSG. I never realized it was a distinct taste. Anyway, here's their result from the abstract:

We have used a combination of bioinformatics, genetic and functional studies to identify PKD2L1, a polycystic-kidney-disease-like ion channel4, as a candidate mammalian sour taste sensor. In the tongue, PKD2L1 is expressed in a subset of taste receptor cells distinct from those responsible for sweet, bitter and umami taste. To examine the role of PKD2L1-expressing taste cells in vivo, we engineered mice with targeted genetic ablations of selected populations of taste receptor cells. Animals lacking PKD2L1-expressing cells are completely devoid of taste responses to sour stimuli. Notably, responses to all other tastants remained unaffected, proving that the segregation of taste qualities even extends to ionic stimuli.

They also found that other areas of the body use the channel specificall for detecting a lower or acidic pH. This paper may seem to be on a silly topic, but it really is an extremely good example of a thorough and interesting piece of work.

In Nature News, Kendall Powell covers the current neurological understanding of the teenage brain. The literature suggests that while a teen brain is much like an adult's, it isn't quite there yet. Specifically, teens need to recruit a lot more brain power to restrain impulses and make decisions than adults do, possibly explaining their tendency to make obvious, and often dangerous mistakes.

The 14-year-old has a very simple decision to make. When he sees a light out of the corner of his eye he is supposed to ignore it and keep looking straight ahead. It seems extraordinarily easy — even eight-year-olds can do it correctly half of the time — but it requires reigning in a natural impulse to look. And every parent of a teenager knows that reigning in impulses is not their strong suit.

In this simple test, the teenager performs as well as adults do. But a peek inside his head reveals that he puts a lot more work into it. His brain uses a whole host of frontal regions — those involved in planning and executing actions — that adults ignoring something in their peripheral vision just don't need.

"The adolescent brain is acting like an adult brain doing something much more difficult. An adolescent can look so much like an adult, but cognitively, they are not really there yet," says Bea Luna, a neuroscientist at the University of Pittsburgh Medical Center in Pennsylvania. It is her brain scans that have revealed this tendency for teenagers to 'overuse' their frontal brain regions when stopping themselves from looking at the light

Further, evidence does exist that girls brains undergo the maturation to an adult brain sooner than boys.

The NIMH research team, led by Jay Giedd, has made a movie of normal brain changes from ages 5 to 20 (ref. 3). It reveals that the grey matter thickens in childhood but then thins in a wave that begins at the back of the brain and reaches the front by early adulthood (see graphic, below). The process completes itself sooner in girls than in boys. This corresponds to a long-held assumption that adolescence sees the prefrontal cortex regions that handle executive functions 'waking up' and to the conventional wisdom that girls mature faster in this respect.

This process seems to occur through a refining and selection of neural pathways through myelination, essentially coating selected neural pathways with insulation, that facilitates transduction of signals through neurons.

As grey matter thins, white matter is being gained, as layers of insulating myelin are added to the axon connections between nerve cells. George Bartzokis, a neuroscientist at the University of California, Los Angeles, has found that such 'myelination' follows an inverted 'U' shape over our lifetimes, peaking at around age 50 (ref. 6). The teen years are on the early stages of the steep upward curve of myelination.

Bartzokis see this as facilitating connections between different parts of the brain: if you want to retrieve pertinent information quickly to make a decision, he argues, you don't want a supercomputer "but rather a fast Internet". Information held in different centres of the brain has to be 'online' or retrievable, and retrieving lots of it quickly requires increased processing speed and bandwidth. Myelination provides this by increasing the speed of signals travelling along axons and decreasing the time to the next nerve impulse.

But that's not all, functional MRI of teen brains says some of the reason they behave as they do is that they have a lower threshold for pleasure than children or adults.

Other functional studies link changes in the brain to teenagers' increased appetite for fast cars and other dangerous thrills. B. J. Casey's group at Weill Medical College of Cornell University in New York has measured brain activity in subjects who perform a simple task and then get small, medium or large rewards for performing correctly. In adolescents given a medium or large reward, a centre in the brain called the nucleus accumbens reacted more strongly than in children or adults8. That looks like an exaggeratedly positive reaction. When given the small reward, the teenage accumbens response decreased below that of children and adults — as if the small reward represented no reward at all in the teen's view.

All interesting stuff, this week's edition is worth a full read.