Chris Blattman

My brain is shedding neurons (tell me something I don’t know edition)

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.)

4 Responses

  1. Just a tiny point! The “the first 3 years are the only 3 years where you can have any effect” deal in child development is fairly widely recognized to have been overblown, I think. Different parts of the brain “loose neurons” at different rates & the prefrontal cortex (very important for working memory) is probably not at its most developed & efficient until early adulthood. For some kinds of input and some kinds of skills you are going to have a hard time after 3 years old but that is not the end of the story!

  2. this point comes up a lot in the early childhood research (and advocacy), justifying the need for early intervention. the argument mainly goes that after six, you can still have an impact on someone’s cognitive ability, but it requires more sustained attention and is more expensive. (i can send you a ppt if you are interested. it is not my research tho). naturally, this also comes up in the parenting literature as to why you should stimulate your baby and toddler.

    i dont know of any evidence on multitasking, but there seem to be a lot of religious/spiritual professions that it is bad. think about the whole point of meditation; see “the power of now” etc. i skimmed the “now habit” and i think the advice seems plausible (you dont get stuff done if you dont focus and that requires dedicated attention for some time), but of course there are lots of extremely productive people who are very productive and still multitask.

  3. I’m not surprised to hear that there’s no evidence that women are better at multitasking, but don’t you think (and we’re veering dangerously into anecdotal evidence, so I apologize) that women are more *likely* to multitask, abilities aside?

    I’m thinking about a poster I saw once, which depicts a man and a woman making morning coffee, in different houses. The man puts on the coffee, stands beside the pot until it’s finished, and then pours two cups. The woman puts on coffee, empties the cat litter, takes out the garbage, brings in the mail, packs a lunch, etc., and finishes up in time to pour two cups of coffee.

    This is cultural, presumably, related to the second shift and the number of competing priorities that women are juggling.

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