The Economist looks at Blossoming brains:
By about the age of six, the human brain is as big as it is ever going to be. That may surprise most grown-ups, who notice that children do not display the mental agility of adults (even though many fancy their own little angels are geniuses). Children can remember facts but are less good at recalling the context in which those facts are relevant. And they are easily swayed from long-term goals. Even when youngsters try their hardest they cannot wait 15 minutes for two biscuits if they can scoff one now instead. But as people grow, their brains change. Before full volume is attained, the pruning starts. Grey matter gets picked away at different rates in different parts of the organ. Brain cells form white matter as their arms become covered in fatty sheaths that, like the plastic insulation around a metal wire, stop electrical signals leaking out as they zip along the nerve cells. As the grey matter diminishes, the white matter steadily increases. Which is why the brain can mature from an organ of overwhelmingly short-range connections into one with many long-distance links, as Bradley Schlaggar and his colleagues at Washington University, in St Louis, have found.Dr Schlaggar likes to create diagrams of brain function using a technique called graph theory that is used, among other things, to analyse demand on power grids and the structure of the Internet. He asks volunteers to lie in brain scanners and to think about whatever they wish. Then he tries to identify which parts of the brain are simultaneously active — or almost so. Where activity exceeds certain statistical thresholds, he plots a line between those bits of the brain on his diagrams.
This approach has led Dr Schlaggar to suggest why it is that adults can better resist impulses that derail long-term goals in children. His work is based on an idea by his colleague Steven Petersen, who recently developed the hypothesis that two networks, rather than two areas of the brain (as the mainstream theory has it), keep the adult mind concentrated on long-term achievement.
Dr Petersen and his colleagues identified 39 regions of the brain that were active when university students applied themselves to ten different tasks, each with varying levels of surprise built in. Whether the students were listening to repetitive sounds and trying to predict when the next tone would come, or pushing the correct button if pairs of words were matched or mismatched in their meanings, some consistent synchronisation emerged. Seven of the 39 regions looked busy when the brain was pursuing a successful strategy and maintaining a consistent effort. Eleven other parts chipped in when that strategy slipped up and some innovation was needed for the student to complete the task. Dr Petersen postulated that the first seven regions form one network, which he calls the “cingulo-opercular network”, and the second 11 form another, the “frontoparietal network”.
Dr Schlaggar next wondered how the connections within these two networks might develop. So he turned to a second group, made up of children and teenagers, and asked them to think about whatever they liked while he scanned the blood flow inside the same 39 regions of their brains and calculated which parts were acting in unison.
What he found came as a shock. In the 49 children, aged seven to nine, the two networks were always bound into a single web; in the 43 adolescents, some of those connections had been undone; and in his 47 adult volunteers, aged over 21, the brain regions fired as two distinct networks. Moreover, the web of activity inside the children’s heads depicted the cingulo-opercular (sustaining) network as being clamped inside the frontoparietal (rapidly adapting) one, suggesting why it is that youngsters grab one biscuit now rather than wait for two later. Both studies were published recently in the Proceedings of the National Academy of Sciences.