UPDATE | Sam Wang responds to readers’ comments: here, here and here.

Many thanks to Steve Quake for four stimulating articles on some of the dilemmas facing scientists today. He now hands off to Sandra Aamodt and Sam Wang, two neuroscientists famous for their award-winning book, “Welcome to Your Brain: Why You Lose Your Car Keys But Never Forget How to Drive and Other Puzzles of Everyday Life.” Sandra and Sam will be writing their articles together; please welcome them.

Olivia

By Sam Wang and Sandra Aamodt

It’s an honor to be invited to fill in for Olivia. We’ll be writing about slow and fast forces that shape the brain: natural selection, operating relatively slowly over many generations; and environmental influences, whose effects are visible across a few generations or even within one individual’s lifetime.

We’re often asked whether the human brain is still evolving. Taken at face value, it sounds like a silly question. People are animals, so selection pressure would presumably continue to apply across generations.

But the questioners are really concerned about a larger issue: how our brains are changing over time — and whether we have any control over these developments. This week we discuss intelligence and the “Flynn effect,” a phenomenon that is too rapid to be explained by natural selection.

It used to be believed that people had a level of general intelligence with which they were born that was unaffected by environment and stayed the same, more or less, throughout life. But now it’s known that environmental influences are large enough to have considerable effects on intelligence, perhaps even during your own lifetime.

A key contribution to this subject comes from James Flynn, a moral philosopher who has turned to social science and statistical analysis to explore his ideas about humane ideals. Flynn’s work usually pops up in the news in the context of race issues, especially public debates about the causes of racial differences in performance on intelligence tests. We won’t spend time on the topic of race, but the psychologist Dick Nisbett has written an excellent article on the subject.

Flynn first noted that standardized intelligence quotient (I.Q.) scores were rising by three points per decade in many countries, and even faster in some countries like the Netherlands and Israel. For instance, in verbal and performance I.Q., an average Dutch 14-year-old in 1982 scored 20 points higher than the average person of the same age in his parents’ generation in 1952. These I.Q. increases over a single generation suggest that the environmental conditions for developing brains have become more favorable in some way.

What might be changing? One strong candidate is working memory, defined as the ability to hold information in mind while manipulating it to achieve a cognitive goal. Examples include remembering a clause while figuring out how it relates the rest of a sentence, or keeping track of the solutions you’ve already tried while solving a puzzle. Flynn has pointed out that modern times have increasingly rewarded complex and abstract reasoning. Differences in working memory capacity account for 50 to 70 percent of individual differences in fluid intelligence (abstract reasoning ability) in various meta-analyses, suggesting that it is one of the major building blocks of I.Q. (Ackerman et al; Kane et al; Süss et al.) This idea is intriguing because working memory can be improved by training.

Felix Sockwell

A common way to measure working memory is called the “n-back” task. Presented with a sequential series of items, the person taking the test has to report when the current item is identical to the item that was presented a certain number (n) of items ago in the series. For example, the test taker might see a sequence of letters like

L K L R K H H N T T N X

presented one at a time. If the test is an easy 1-back task, she should press a button when she sees the second H and the second T. For a 3-back task, the right answers are K and N, since they are identical to items three places before them in the list. Most people find the 3-back condition to be challenging.

A recent paper reported that training on a particularly fiendish version of the n-back task improves I.Q. scores. Instead of seeing a single series of items like the one above, test-takers saw two different sequences, one of single letters and one of spatial locations. They had to report n-back repetitions of both letters and locations, a task that required them to simultaneously keep track of both sequences. As the trainees got better, n was increased to make the task harder. If their performance dropped, the task was made easier until they recovered.

Each day, test-takers trained for 25 minutes. On the first day, the average participant could handle the 3-back condition. By the 19th day, average performance reached the 5-back level, and participants showed a four-point gain in their I.Q. scores.

The I.Q. improvement was larger in people who’d had more days of practice, suggesting that the effect was a direct result of training. People benefited across the board, regardless of their starting levels of working memory or I.Q. scores (though the results hint that those with lower I.Q.s may have shown larger gains). Simply practicing an I.Q. test can lead to some improvement on the test, but control subjects who took the same two I.Q. tests without training improved only slightly. Also, increasing I.Q. scores by practice doesn’t necessarily increase other measures of reasoning ability (Ackerman, 1987).

Since the gains accumulated over a period of weeks, training is likely to have drawn upon brain mechanisms for learning that can potentially outlast the training. But this is not certain. If continual practice is necessary to maintain I.Q. gains, then this finding looks like a laboratory curiosity. But if the gains last for months (or longer), working memory training may become as popular as — and more effective than — games like sudoku among people who worry about maintaining their cognitive abilities.

Now, some caveats. The results, though tantalizing, are not perfect. It would have been better to give the control group some other training not related to working memory, to show that the hard work of training did not simply motivate the experimental group to try harder on the second I.Q. test. The researchers did not test whether working memory training improved problem-solving tasks of the type that might occur in real life. Finally, they did not explore how much improvement would be seen with further training.

Research on working memory training, as well as Flynn’s original observations, raise the possibility that the fast-paced modern world, despite its annoyances (or even because of them) may be improving our reasoning ability. Maybe even multitasking — not the most efficient way to work — is good for your brain because of the mental challenge. Something to think about when you’re contemplating retirement on a deserted island.

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Clarification: We wrote that in the complex version of the n-back task, test-takers “saw” two sequences of stimuli. In fact, the letter sequence was heard. Thanks to commenter Adam Thomas for pointing this out.

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NOTES:

C. Jarrold and J.N. Towse (2006) Individual differences in working memory. Neuroscience 139 (2006) 39–50.

P.L. Ackerman, M.E. Beier, and M.O. Boyle (2005) Working memory and intelligence: the same or different constructs? Psychological Bulletin 131:30–60.

M.J. Kane, D.Z. Hambrick, and A.R.A. Conway (2005) Working memory capacity and fluid intelligence are strongly related constructs: comment on Ackerman, Beier, and Boyle (2005). Psychological Bulletin 131:66–71.

H.-M. Süss, K. Oberauer, W.W. Wittmann, O. Wilhelm, and R. Schulze (2002) Working-memory capacity explains reasoning ability—and a little bit more. Intelligence 30:261–288.

S.M. Jaeggi, M. Buschkuehl, J. Jonides, and W.J. Perrig (2008) Improving fluid intelligence with training on working memory. Proceedings of the National Academy of Sciences USA 105:6829-6833.

D.A. Bors, F. Vigneau (2003) The effect of practice on Raven’s Advanced Progressive Matrices. Learning and Individual Differences 13:291–312.

P.L. Ackerman (1987) Individual differences in skill learning: An integration of psychometric and information processing perspectives. Psychological Bulletin 102:3–27.