Metabolic costs of human brain development

This paper quantifies the unusually high energetic cost of brain development in humans. Brain energy requirements and body-weight growth rate are anti-correlated in childhood. Given these results it would be surprising if nutritional limitations that prevented individuals from achieving their genetic potential in height didn't also lead to sub-optimal cognitive development. Nutritional deprivation likely stunts both mind and body.

See also Brainpower ain't free.

Metabolic costs and evolutionary implications of human brain development
(PNAS doi:10.1073/pnas.1323099111)

Significance
The metabolic costs of brain development are thought to explain the evolution of humans’ exceptionally slow and protracted childhood growth; however, the costs of the human brain during development are unknown. We used existing PET and MRI data to calculate brain glucose use from birth to adulthood. We find that the brain’s metabolic requirements peak in childhood, when it uses glucose at a rate equivalent to 66% of the body’s resting metabolism and 43% of the body’s daily energy requirement, and that brain glucose demand relates inversely to body growth from infancy to puberty. Our findings support the hypothesis that the unusually high costs of human brain development require a compensatory slowing of childhood body growth.

Abstract
The high energetic costs of human brain development have been hypothesized to explain distinctive human traits, including exceptionally slow and protracted preadult growth. Although widely assumed to constrain life-history evolution, the metabolic requirements of the growing human brain are unknown. We combined previously collected PET and MRI data to calculate the human brain’s glucose use from birth to adulthood, which we compare with body growth rate. We evaluate the strength of brain–body metabolic trade-offs using the ratios of brain glucose uptake to the body’s resting metabolic rate (RMR) and daily energy requirements (DER) expressed in glucose-gram equivalents (glucosermr% and glucoseder%). We find that glucosermr% and glucoseder% do not peak at birth (52.5% and 59.8% of RMR, or 35.4% and 38.7% of DER, for males and females, respectively), when relative brain size is largest, but rather in childhood (66.3% and 65.0% of RMR and 43.3% and 43.8% of DER). Body-weight growth (dw/dt) and both glucosermr% and glucoseder% are strongly, inversely related: soon after birth, increases in brain glucose demand are accompanied by proportionate decreases in dw/dt. Ages of peak brain glucose demand and lowest dw/dt co-occur and subsequent developmental declines in brain metabolism are matched by proportionate increases in dw/dt until puberty. The finding that human brain glucose demands peak during childhood, and evidence that brain metabolism and body growth rate covary inversely across development, support the hypothesis that the high costs of human brain development require compensatory slowing of body growth rate.

Height, Flynn Effect, and shared environment

Some interesting examples of shared environmental effects on height.

Atlantic: ... a database of 2,236 British soldiers who served in World War I, and then they looked up their birth records. The soldiers were relatively representative of the male population as a whole—about two-thirds of the 1890 British male birth cohort enlisted. It turns out that subtle differences in their heights hinted at their origins:

Those from white-collar backgrounds were taller: This follows the theory that wealth buys better food and living conditions, and thus greater height in adulthood. The men who hailed from the top two social classes stood a half-inch taller, on average.

The more kids there were in a household, the shorter they were: Not only because there was less food to go around, but also because it made it more likely that there were more people in each bedroom. “Crowding can help spread respiratory and gastrointestinal infections,” Hatton said. “People sneezing on each other, that sort of thing.” Each additional sibling cost the men an eighth of an inch, and having more than one person per bedroom shaved off a quarter-inch.

Children of literate mothers were taller: When mothers couldn’t read, they were less likely to know about the importance of a balanced diet or clean cutlery. The researchers measured the percentage of women by region who were only able to sign their marriage certificates with an X, rather than their name. People from areas with a high percentage of illiterate mothers were a quarter-inch shorter.

People from industrial districts were shorter than those from agricultural areas: Regardless of income, the Dickensian living conditions of 19th century British cities suppressed height by about nine-tenths of an inch.

Average European male height increased 11 centimeters between 1870 and 1970, about a centimeter per decade, or 1.5 SD in a century. Seems suspiciously similar to the Flynn Effect! In addition, over the same period of time average years of schooling went up significantly: e.g., UK 1870 4 years to 1930 7 years (see Appendix A of this paper). Most individuals born 100 years ago experienced significant deprivation by modern standards.

My own view is that there is nothing particularly mysterious about the Flynn Effect: living conditions, nutrition, and availability of education have all improved drastically in the last 150 years. So g scores should have as well. The Flynn Effect can be consistent with high heritability for non-deprived individuals in modern environments.

See also Swedish height in the 20th century and Flynn on the Flynn Effect.

The north-south gradient in average height found in Europe (see figure) may be a consequence of differential selection pressures that vary by region.

Sven Magnus Øen Carlsen

I am curious about what serious chess players think of Elo scores across generations -- is there a Flynn Effect? Current world champ Magnus Carlsen has the highest score of all time. It seems possible that due to computer training today's players are much better than those of the past -- we'll never know how giants like Bobby Fischer would have developed using today's methods. By Elo score Fischer is only 14th on the all-time list!

I thought interest in chess would decline after Deep Blue defeated Kasparov. But apparently the game is still thriving.

The excerpts below are from an old interview in Der Spiegel:

Carlsen: ... my success mainly has to do with the fact that I had the opportunity to learn more, more quickly. It has become easier to get hold of information. The players from the Soviet Union used to be at a huge advantage; in Moscow they had access to vast archives, with countless games carefully recorded on index cards. Nowadays anyone can buy this data on DVD for 150 euros; one disk holds 4.5 million games. There are also more books than there used to be. And then of course I started working with a computer earlier than Vladimir Kramnik or Viswanathan Anand.

SPIEGEL: When exactly?

Carlsen: I was eleven or twelve. I used the computer to prepare for tournaments, and I played on the Internet. Nowadays, children start using a computer at an even earlier age; they are already learning the rules on screen. In that sense I am already old-fashioned. Technological progress leads to younger and younger top players, everywhere in the world.

SPIEGEL: Is being young an advantage in modern chess?

Carlsen: As a young player you have a lot of energy, a lot of strength, you are very motivated. But young players are often not good at defending a position; they cannot cope well when fate turns against them. The fact is simply that experience is a central issue. One of the most important things in chess is pattern recognition: the ability to recognise typical themes and images on the board, characteristics of a position and their consequences. To a certain degree you can learn that while training, but there is nothing like playing routine. I have always made sure to get that. I am only 19, but I have certainly already played a thousand games in the classic style.

This is also interesting:

SPIEGEL: Mr Carlsen, what is your IQ?

Carlsen: I have no idea. I wouldn’t want to know it anyway. It might turn out to be a nasty surprise.

SPIEGEL: Why? You are 19 years old and ranked the number one chess player in the world. You must be incredibly clever.

Carlsen: And that’s precisely what would be terrible. Of course it is important for a chess player to be able to concentrate well, but being too intelligent can also be a burden. It can get in your way. I am convinced that the reason the Englishman John Nunn never became world champion is that he is too clever for that.

SPIEGEL: How that?

Carlsen: At the age of 15, Nunn started studying mathematics in Oxford; he was the youngest student in the last 500 years, and at 23 he did a PhD in algebraic topology. He has so incredibly much in his head. Simply too much. His enormous powers of understanding and his constant thirst for knowledge distracted him from chess.

SPIEGEL: Things are different in your case?

Carlsen: Right. I am a totally normal guy. My father is considerably more intelligent than I am.

Der Spiegel carefully tested Kasparov's IQ at 135, as discussed here. See also The Laskers and the Go master.

Annals of psychometry: adult cognitive skills by country

You may have read (NYTimes; enjoy the 500 expert comments!) about the recent OECD study of adult skills, which showed Americans lagging behind most other advanced countries. The outcomes more or less recapitulate the PISA results, which are produced by the same organization, led by Andreas Schleicher (Without data, you are just another person with an opinion; Schleicher was trained in physics before moving into educational assessment). Studying adults rather than students makes generational differences apparent: young Koreans scored near the top in the world, whereas older Koreans, who grew up in a much poorer country, do less well. This was also true for Finns, but countries like the UK, US and Australia showed almost no difference between the young and old. It would appear that the Flynn Effect has abated for the current adult population in those countries.

The most striking findings in the report to someone already familiar with this kind of country level data, are that:

(I) Job growth in areas requiring superior ability is high, whereas there is almost no growth in other sectors (see figure below and figure 1.3 in the report). The biggest decline in jobs is in manufacturing-related areas, which are characterized by low, but not the lowest, scores. The number of menial jobs, characterized by the lowest scores, held their own. In other words, in developed countries jobs for factory workers declined while maids, gardeners and servants held their own... a grim future of income inequality based on cognitive ability?

(Difference between mean scores of skilled and "elementary" occupations is about 1 population SD -- Table A3.19. This is about the same as mean score difference between college graduates and those that did not reach upper secondary education! Table A3.9 (l))

(II) Scores on numeracy and literacy showed high correlations: 0.8 -- 0.9 in every country. This is much higher than, for instance, M and V correlation on the SAT.

Here are national score ranges for math skills:

This figure shows that Japanese high school graduates have better literacy skills than Italian college graduates. There is plenty more data like this. Interestingly the standard deviations in scores for Japan and Korea are on the low end compared to other countries.

Roughly every fifth Finn and Japanese reads at high levels (Level 4 or 5 on the Survey of Adult Skills). This means, for example, that they can perform multiple-step operations to integrate, interpret, or synthesise information from complex or lengthy texts that involve conditional and/or competing information; and they can make complex inferences and appropriately apply background knowledge as well as interpret or evaluate subtle truth claims or arguments. They are also good at numbers: they can analyse and engage in complex reasoning about quantities and data, statistics and chance, spatial relationships, change, proportions and formulae; perform tasks involving multiple steps and select appropriate problem-solving strategies and processes; and understand arguments and communicate well-reasoned explanations for answers or choices.

How does someone who can't do these things obtain a good college degree? If only 20% of Finns and Japanese can do these things (the largest fraction among all nations), what fraction of US students are ready for serious college work?

Swedish height in the 20th century

Average height of Swedish military conscripts during the 20th century. Looks like an increase of roughly 1 cm per decade or about 1.5 SD in one century. Not unlike the Flynn Effect over the same period.

It was important to generate this curve so that we could properly z score heights of individuals from different birth cohorts. Thanks to my collaborator Laurent Tellier.

Slumdog brainpower

I found the comment below interesting. Currently I think the effective population of India for producing elite brainpower (i.e., comparing to a reference population with average IQ = 100 and access to first world education and training) is roughly 100 million. For China this number might be 300+ million, but we don't feel their presence in the West as strongly because of language barriers and because of the ability of the Chinese economy to absorb many of the high achievers domestically. (Despite all the Chinese scientists and engineers emigrating to the West there are just as many staying at home to develop a continent-sized economy with a space program, high speed trains, tech and defense industry, etc.) Both the China and India numbers should increase drastically in another generation, although see below for challenges confronting India.


See these related posts, or click the India label below.

More where those came from

IIT uber alles

To have and have not

Shanghai from an Indian perspective

Battle for brainpower

Background: I come from Southern India, high achiever, made a pile as they would say, so broadening my attention to study these subjects to understand the cause of our underdevelopment and what we can do about it. I only have experience with Southern India, where I live and travel extensively; I also get to travel the world extensively so I can give detailed comparisons. While I obviously do want to help my country, I am of the "Face Reality As It Is" persuasion, so I don't worry about political correctness of any discussion here.

First, the good news: thanks to better nutrition, I have witnessed IQ go up substantially in the past 30 years. The typical South Indian immigrant you see in the US today (and they do seem to come mostly from the South these days) comes from a vastly lower social scale than the one you saw 40 years ago. The typical immigrant has parents or grandparents who would not be able to function well in Western society, because they lack the cognitive skills. So the Flynn effect seems very visible to me, from my vantage point in South India.

Second, there are even more gains to be had. Malnutrition is slowly going away in the South, but in the North, it is still very very prevalent - we are talking more than 50% of kids malnourished.

Third, a pacific temperament and a traditional respect for authority keeps lower IQ populations from the pervasive social breakdown you see in the US in similarly situated communities. Families are staying intact; if that changes in India in any large scale, I would write India off, because collectively, we Indians are still too dumb to handle "sophisticated" mating behavior (though I think even the Swedish men stay together with their mates to support their kids, in spite of the promiscuous reputation of their society) - I hope our Hindu Gods literally save us on this one!

Now the bad news. Democracy empowers the dumb, probably true everywhere, but truer in India. The elected need to be skillful at manipulating the dumb, so they tend to be smarter than those electing them. Still, all this manipulating exacts a toll. One of the manipulating they do is jobs-for-dumb-constituents, which begets appallingly bad government, particularly at local levels.

This has all sort of bad effects. With such bad local governance, much of India looks like an ungoverned mess - your senses get physically assaulted in almost any urban space in India, disgusting levels of filth and squalor. This is the result of the utter inability to plan, explained by the IQ of those in charge at local levels.

This is more serious than even that. As India urbanizes, we risk going back on Flynn effect, because poor sanitation leads to *urban* malnutrition - not lack of food, but gastrointestinal illness among kids - which lowers IQ. So not having functional lower levels of government puts India's progress at risk. This, I attribute, directly to democracy.

Given these two opposing forces, which was is it going to go? I believe the good edges out the bad, but that would be a hard case to make when you see the filth.

Only good news I can gather is that London and Hong Kong and so on were extremely filthy at a point in their development too.

Psychometrics links

Retired physicist Bob Williams writes: "... I have studied psychometrics and intelligence research for about 17 years and have gotten to know almost all of the current researchers through my membership in the International Society for Intelligence Research. I attend the conferences and discuss the recent studies with the people who have done them."

He sent me the following interesting links:

Summary of research on heritability of intelligence

Diminishing influence of g at high end of ability

Summary of research on evolution of human intelligence


From Williams' notes on ISIR 2007: a discussion with James Flynn:

The interviewer was David Lubinski (Vanderbilt). He started the interview by asking Flynn to tell us about his life. From that point on, Lubinski only managed to get in a dozen or so words. Once the camera started, Flynn launched into an enthusiastic discussion of himself and his ideas. He made a favorable impression from the start by telling us that he grew up in a Catholic family and has become a serious atheist. He also immediately told us of his well known (socialist) political orientation and did not ever attempt to disconnect his political notions from his thoughts about intelligence and the secular rise that bears his name. Flynn speaks clearly and with a loud voice, which was well suited for the interview and later became something of a tool for overpowering people with whom he disagreed. In spite of this, I found him to be very likable, smart, and complicated. He occasionally took positions that were diametrically opposed and admitted that he had done so.

Flynn mentioned his first article (1984), showing a 14 point gain over 30 years (I may have gotten the span wrong, but I think this is correct). In 1987 he published a paper that showed the largest gains were on the Raven’s tests. He has found little, if any, gain in vocabulary. It is well known that FE (Flynn Effect) gains have been greatest in tests of abstract reasoning and least in tests that relate to scholastic items. This contrast immediately suggests that the FE gains have not been g loaded, since g loaded gains would necessarily boost all cognitive tasks. Flynn has not discussed this. I asked him what portion of the gains were g loaded and he went into his history discussion, then finally said “I don’t know.”

Flynn has approached the FE as a matter to be discussed qualitatively, without the support of carefully constructed research studies. Throughout his talk (this was an interview, but it turned into a speech), he described intelligence as a factor with historical variability. His debate with Charles Murray is available on the web and contains the same illustrations that he used in the “interview.” His bottom line is that test items have become easier over time, not because people are more intelligent, but because the items being tested have taken on a more central role in their lives. This makes sense with some test items (vocabulary, for example, but that is one area where he has found little increase), but is not at all apparent with respect to other test items, some of which are unrelated to daily experiences (just look at the list of subtests used in the W-J III).

He mentioned reaction time tests and simply discarded them as not important. This is not so easy to accept, given that a battery of RT tests can produce a very highly g loaded discrimination, yet chronometric measures have not been shown to change over decades. Meanwhile, Flynn was positive about the future of brain imaging and seemed willing to accept future results, even if they support causation that is opposite of his preference. He expects that such research will ultimately find a physiological seat of g. I fully agree, but also find this comment to be in conflict with his arguments from the Dickens-Flynn paper (Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved).

Interestingly, Flynn does not believe that the FE will narrow the B-W IQ gap. Some environmentalists have argued that it will, but no evidence has surfaced to show that after decades of rise, the FE has actually narrowed the gap.

Flynn admitted to having been fired twice and explained that those events prompted him to move to New Zealand. He claims to have defended Larry Summers, James Watson, and Chris Brand. ...In these areas, Flynn shows himself to be both honest and inconsistent. He is inherently likable and extraverted, although I remain of the opinion that he is less interested in discussion than in lecturing. I talked to him for a while at a reception and found him to be pleasant, polite, and sharp.

During his commentary, Flynn said that he favored affirmative action. In fact, he showed a strong interest in finding ways to help blacks overcome various obstacles. When Gottfredson questioned him about affirmative action, he said he is not a fanatic on the subject and admitted that it is unfair to whites. He said that, when employers want to hire a black worker, they are generally unconcerned with whether the employee is outstanding or average.

He attributed at least some of the FE gains to decreasing family size and noted that it cannot go much lower. When I had a chance to talk to him, I asked what portion of the FE gains he believes are g loaded. After repeating his historical perspective, he said “I don’t know.”

From notes on ISIR 2008

Jan te Nijenhuis

The Flynn effect in Korea

• United States FE rate, 3 points per decade.
• Scandinavia, recent slight reversal (IQ decrease).
• Estonia, recent gains.
• Japan, for those born from 1940 to 1965, 7.7 points per decade.
• Korea and Japan, same gains.
• Korea experienced an explosion in education and height of 1.5 to 2.0 SD.

The study involved two formats. One was to use single Raven’s test comparisons for two groups for 1952 and 1982. The other was to test a single group with two tests that were normed 30 years apart. The Koreans gained at about the same rate as did the Japanese, but delayed by 20 to 30 years. The gains have not yet leveled off or reversed.

Some useful references on this topic:

The Structure and Measurement of Intelligence

Genius: the natural history of creativity,

both by Hans Eysenck.

The g-factor, by Arthur Jensen

Flynn on the Flynn effect

Via GNXP, this lecture by James Flynn. The lecture is long but worth reading in full. His discussion of factor loading in the context of the decathalon, 100m speed, hurdling, etc. is excellent and very relevant to the subject of intelligence and its various cognitive components. The Flynn effect refers to a significant increase in raw IQ scores over the last 100 years or so -- equivalent of 30 points or more, in some cases. This raises a number of thorny issues. Were our ancestors idiots? Is IQ really that malleable under environmental influence (contrary to recent twin studies)? Is the principal component identified as "g" actually time dependent? See Flynn's answers below. A couple of comments: (i) Dramatic gains are seen only in certain areas of intelligence (see table from Sailer discussion), which are plausibly the areas in which modern life provides much more stimulation. (ii) Average people 100 years ago were massively deprived by modern standards -- much more than we could ever reproduce in a modern twin study. US GDP per capita is 10x higher now, and average years of schooling has increased dramatically. It's not surprising that a child who only received (say) 6 years of formal schooling would be far behind someone with 12. Modern twin studies only include kids raised in a much smaller range of environments -- no twin in any recent study had less than the legally mandated US high school education. With a smaller range of environmental effects, the genetic component plays a larger role, leading to the high (.5-.7 or so) heritability result for IQ (similar to height). (Flynn notes: In the America of 1900, adults had an average of about 7 years of schooling, a median of 6.5 years, and 25 percent had completed 4 years or less.) (iii) The analogy with height is quite appropriate. While taller parents tend to have taller children (i.e., height is heritable), we've seen siginificant gains in average height as nutrition and diet have improved. (iv) I think Flynn would agree that variance in adult IQ must have been much larger in the past. People like Newton or Thomas Jefferson obviously had tremendously more exposure to ideas and abstract thinking than a kid on the farm with little or no education, few books, no TV and no radio. The Flynn effect does not imply that the great geniuses of the past were necessarily inferior to those of today.

Lecture by Professor James Flynn at The Psychometrics Centre, Cambridge Assessment, University of Cambridge, 15th December 2006 Naming the paradoxes (1) The factor analysis paradox: Factor analysis shows a first principal component called "g" or general intelligence that seems to bind performance on the various WISC subtests together. However, IQ gains over time show score gains on the WISC subtests occurring independently of one another. How can intelligence be both one and many? (2) The intelligence paradox: If huge IQ gains are intelligence gains, why are we not stuck by the extraordinary subtlety of our children's conversation? Why do we not have to make allowances for the limitations of our parents? A difference of some 18 points in the average IQ over two generations ought to be highly visible. (3) The MR paradox: In 1900, the average IQ scored against current norms was somewhere between 50 and 70. If IQ gains are in any sense real, we are driven to the absurd conclusion that a majority of our ancestors were mentally retarded. (4) The identical twins paradox: Twin studies show that genes dominate individual differences in IQ and that environmental effects are feeble. IQ gains are so great as to signal the existence of environmental factors of enormous potency. How can environment be both so feeble and so potent? The solutions in shorthand (1) The WISC subtests measure a variety of cognitive skills that are functionally independent and responsive to changes in social priorities over time. The inter-correlations that engender "g" are binding only when comparing individuals within a static social context. (2) Asking whether IQ gains are intelligence gains is the wrong question because it implies all or nothing cognitive progress. The 20th century has seen some cognitive skills make great gains, while others have been in the doldrums. To assess cognitive trends, we must dissect "intelligence" into solving mathematical problems, interpreting the great works of literature, finding on-the-spot solutions, assimilating the scientific world view, critical acumen, and wisdom. (3) Our ancestors in 1900 were not mentally retarded. Their intelligence was anchored in everyday reality. We differ from them in that we can use abstractions and logic and the hypothetical to attack the formal problems that arise when science liberates thought from concrete referents. Since 1950, we have become more ingenious in going beyond previously learned rules to solve problems on the spot. (4) At a given time, genetic differences between individuals (within a cohort) are dominant but only because they have hitched powerful environmental factors to their star. Trends over time (between cohorts) liberate environmental factors from the sway of genes and once unleashed, they can have a powerful cumulative effect.

Are we getting smarter? Why?

It is well known that raw scores on IQ tests have been increasing at a rate of what would be about 3 IQ points per decade (the so-called Flynn effect). This means that, were the result of the test not rescaled so that the average is 100 by definition, the average IQ would have risen to 130 over the last century - i.e., the average person today scores better than all but 2 percent or so of the population in 1900. Malcolm Gladwell discusses this effect and its possible causes in this week's New Yorker, reviewing a new book claiming that modern society, with its fast-paced multimedia entertainment (including video games, computers, TV, etc.) actually improves our cognitive skills.

Gladwell: "Twenty years ago, a political philosopher named James Flynn uncovered a curious fact. Americans—at least, as measured by I.Q. tests—were getting smarter. This fact had been obscured for years, because the people who give I.Q. tests continually recalibrate the scoring system to keep the average at 100. But if you took out the recalibration, Flynn found, I.Q. scores showed a steady upward trajectory, rising by about three points per decade, which means that a person whose I.Q. placed him in the top ten per cent of the American population in 1920 would today fall in the bottom third. Some of that effect, no doubt, is a simple by-product of economic progress: in the surge of prosperity during the middle part of the last century, people in the West became better fed, better educated, and more familiar with things like I.Q. tests. But, even as that wave of change has subsided, test scores have continued to rise—not just in America but all over the developed world. What’s more, the increases have not been confined to children who go to enriched day-care centers and private schools. The middle part of the curve—the people who have supposedly been suffering from a deteriorating public-school system and a steady diet of lowest-common-denominator television and mindless pop music—has increased just as much. What on earth is happening? In the wonderfully entertaining “Everything Bad Is Good for You” (Riverhead; $23.95), Steven Johnson proposes that what is making us smarter is precisely what we thought was making us dumber: popular culture.

...As Johnson points out, television is very different now from what it was thirty years ago. It’s harder. A typical episode of “Starsky and Hutch,” in the nineteen-seventies, followed an essentially linear path: two characters, engaged in a single story line, moving toward a decisive conclusion. To watch an episode of “Dallas” today is to be stunned by its glacial pace—by the arduous attempts to establish social relationships, by the excruciating simplicity of the plotline, by how obvious it was. A single episode of “The Sopranos,” by contrast, might follow five narrative threads, involving a dozen characters who weave in and out of the plot. Modern television also requires the viewer to do a lot of what Johnson calls “filling in,” as in a “Seinfeld” episode that subtly parodies the Kennedy assassination conspiracists, or a typical “Simpsons” episode, which may contain numerous allusions to politics or cinema or pop culture. The extraordinary amount of money now being made in the television aftermarket—DVD sales and syndication—means that the creators of television shows now have an incentive to make programming that can sustain two or three or four viewings.

...It doesn’t seem right, of course, that watching “24” or playing a video game could be as important cognitively as reading a book. Isn’t the extraordinary success of the “Harry Potter” novels better news for the culture than the equivalent success of “Grand Theft Auto III”? Johnson’s response is to imagine what cultural critics might have said had video games been invented hundreds of years ago, and only recently had something called the book been marketed aggressively to children: (Johnson) Reading books chronically understimulates the senses. Unlike the longstanding tradition of gameplaying—which engages the child in a vivid, three-dimensional world filled with moving images and musical sound-scapes, navigated and controlled with complex muscular movements—books are simply a barren string of words on the page. . . .

Books are also tragically isolating. While games have for many years engaged the young in complex social relationships with their peers, building and exploring worlds together, books force the child to sequester him or herself in a quiet space, shut off from interaction with other children. . . .

But perhaps the most dangerous property of these books is the fact that they follow a fixed linear path. You can’t control their narratives in any fashion—you simply sit back and have the story dictated to you. . . . This risks instilling a general passivity in our children, making them feel as though they’re powerless to change their circumstances. Reading is not an active, participatory process; it’s a submissive one.

He’s joking, of course, but only in part. The point is that books and video games represent two very different kinds of learning. When you read a biology textbook, the content of what you read is what matters. Reading is a form of explicit learning. When you play a video game, the value is in how it makes you think. Video games are an example of collateral learning, which is no less important."