How do adult brains develop? By strategically losing neurons.
There are almost twice as many interneuronal connections (synapses) in the frontal lobes of a two-year-old as there are in those of a twenty-year-old, yet the two-year-old has a much poorer working memory.
From the age of two, synaptic density gradually decreases, reaching the adult level somewhere around the age of twelve. After a period of early overproduction, neurons, connectors, and synapses disappear with alarming speed. The fiber system connecting the two cerebral hemispheres loses 900,000 axons per day during the first three months.
It is difficult to explain why capacity should increase when neurons disappear, but it is conceivable that the reinforcement of important connections and the deterioration of unimportant connections combine to improve the structure of the brain.
That is Torkel Klingberg in The Overflowing Brain. The nub of the book: the biggest bottleneck in human mental power is probably working memory–the ability to hold our attention, avoid distraction, juggle different instructions and information in our head, and multi-task.
I now understand much better the implications of my hyper-short attention span. Limit mental power it may, but I can take solace that it probably makes me a better blogger.
I’m learning about the brain, something called executive function, plus working memory for an upcoming project with street youth in Monrovia. These are some of the most impulsive, time-inconsistent people I’ve met. A behavioral economist colleague and I are going to see if we can actually shift behavior (and welfare) by changing preferences (as opposed to the usual economic approach, the commitment device). A Harvard neuropsychologist friend recommended Klingberg’s book. (Readers: other recommendations?)
If nothing else, I was very surprised to learn there isn’t a shred of evidence for the oft-made claim that women are biologically better multi-taskers than men. All urban legend.
(In case you’re keeping score: Evolutionary Psychologists 2, Stephen Jay Gould 4,326.)