Intelligence had long been believed to be impervious to training. Then two doctoral candidates at the University of Bern, Susanne Jaeggi and Martin Buschkuehl, rocked the world of cognitive psychology by publishing a study that argued the very opposite: A few minutes per day of playing dual n-back, an exercise designed to put maximum strain on working memory, led to significant improvements on tests of intelligence. More than a decade’s worth of peer-reviewed research followed — and, with some caveats, corroborated the gist of the initial findings.
Intelligence Is Subject to Interventions
The discussion around the malleability of intelligence dates back to the late 19th century, when Francis Galton argued that intelligence was strictly hereditary, reflecting a determinism that pervaded cognitive psychology for much of the 20th century. (Note that, when referring to intelligence in this article, we mean fluid intelligence — i.e., the ability to reason though novel problems independently of previously acquired knowledge. This is in contrast to crystallized intelligence, which refers to the knowledge from prior learning and past experiences.)
At some point, however, evidence started accumulating that intelligence may actually be less like the color of your eyes and more like your height: Yes, there is a large genetic component, but interventions such as exercise and nutrition play an important role as well.
It nevertheless came as a shock when, in May 2008, Susanne Jaeggi, Martin Buschkuehl, two doctoral candidates at the University of Bern in Switzerland, published a ground-breaking study in the Proceedings of the National Academy of Sciences which suggested that intelligence can be raised through cognitive training as well. Not only that, but only a few hours were required to obtain significant effects. And the effect seemed to be dosage-dependent: The more people practiced, the stronger the results.
Jaeggi and Buschkuehl’s training regimen consisted of a working memory exercise called dual n-back, which requires memorizing and manipulating visuospatial and auditory-verbal stimuli. The task itself is not new: Since 1958, it had been used to test working memory. But just as push-ups, for example, can be used both to test your physical fitness and to build it, Jaeggi and Buschkuehl tried deploying dual n-back as a way to improve working memory — and, by extension, your intelligence.
There had already been prior research pointing to a link between working memory and intelligence. According to Randall Engle, for example, variations in fluid intelligence largely reflect variations in working memory capacity. Others have argued that working memory constraints impair the development of reading, language, and mathematical skills.
Of course, intelligence is more than just working memory. But consider, for a moment, the analogy of physical training: Regular running, for example, can improve your cycling performance — or indeed any other activity that benefits from an efficient cardiovascular system. Training your working memory to improve your intelligence, in that sense, can be seen as the cognitive analogue to training your cardiovascular system to improve your ability to engage in all kinds of physical activities.
Early Studies on Dual N-Back
In their original study, Jaeggi and Buschkuehl divided 70 participants into a training group that practiced the dual n-back task and a control group that merely took the pre- and post-tests. Within the training group, they further applied four different training settings, which differed in the number of dual n-back sessions, ranging from 8 to 19. The pre- and post-tests consisted of matrix problems that are commonly used in standardized IQ tests. In the pre-tests, participants were able to solve between 9 and 10 matrix questions. In the post-tests, participants from the training group experienced a substantial improvement in their performance. And the more sessions they completed, the better their score: Those that completed 19 training sessions were able to solve an additional 4.4 matrix questions.
The results of this initial study were sensational. But the study was later criticized, correctly, for having several methodological flaws. To cite but one example, the control group was merely a passive one. Could it be that the difference in results was mostly attributable to motivational or “Hawthorne” effects?
Jaeggi and Buschkuehl subsequently conducted additional studies to address these limitations and to explore the link between cognitive training, working memory, and intelligence in greater detail. Among other things, they found that the positive effects of n-back training on intelligence remain remarkably stable over time. In a 2011 study that enrolled 76 elementary and middle school children, for example, they conducted a follow-up test three months after the initial post-test and established that the impact on intelligence remained intact.
Other researchers also chimed in. For example, cognitive training was found to be beneficial for specific segments of the population such as the elderly, individuals with attention deficits, and patients with brain injuries.
Meta-Analyses on Dual N-Back
That being said, not all researchers were able to replicate the findings from Jaeggi and Buschkuehl’s studies. So in 2014, the pair teamed up with Jacky Au and colleagues to conduct a comprehensive meta-analysis. They concluded that the effect of dual n-back was both real and meaningful — about 3 to 4 points on a standardized IQ test.
They also discovered several factors that mediated the effect. For example, monetary rewards were inversely correlated with the extent of the cognitive improvements. This suggests that motivation plays a key role in dual n-back: Unless you are intrinsically motivated, you will lack the “grit” needed to push yourself on what is, after all, a highly stressful task. This seems intuitively plausible: If you visit the gym without intrinsic motivation, for example, you won’t push yourself as hard when doing the physical exercises, and you are bound to build less muscle as a result.
The methodology of this initial meta-analysis was later challenged by other researchers who arrived at different conclusions. The culmination point as of today was a 2017 multi-level analysis by Anna Soveri and colleagues. Covering data from 2,105 individuals, it represents not only the most recent, but also the methodologically most rigorous meta-analysis to date. It concluded that n-back training has indeed a significant positive effect on intelligence.
As for the effect size, the authors calculated a Hedge’s g of 0.16, which they characterize as “small.” This characterization needs to be put into perspective, however. According to a commonly used rule of thumb proposed by Jacob Cohen, a Hedge’s g of around 0.2 should indeed be considered “small.” But, as Cohen himself points out, it very much depends on the context: A “small” reduction in suicide rates, for example, is actually invaluable.
Indeed, it’s astonishing that there is any effect of cognitive training on what had been assumed to be an immutable trait at all. In the words of Dan Hurley, author of an early New York Times article on the implications of Jaeggi and Buschkuehl’s research: “To find that training on a working memory task could result in an increase in intelligence would be cognitive psychology’s equivalent of discovering particles traveling faster than light.”
What’s more, the mean training time of individuals covered in the meta study was a mere 6.67 hours! It would be risible to expect less than 7 hours of practice — not much more than the length of a single school day — to result, say, in a 10% increase in IQ. Again, consider physical exercise for an analogy: It’s well-established that jogging improves your level of fitness. But surely you wouldn’t expect to go from couch potato to Olympic hopeful after 7 hours of running practice.
On balance, it could be argued that there is almost nothing you can do with a time budget of 7 hours that will have as large of an impact on your life as completing a dual n-back program — which is precisely why we decided to build the N-Back Challenge, an app designed to nudge you through 20 sessions of dual n-back in a way that is both fun and scientifically rigorous.
Neuroimaging Studies on Dual N-Back
More recent studies have shifted their attention from whether n-back training has an effect to how that effect is generated. Using modern fMRI technology, these studies are shedding light on the neural changes triggered by the training.
In a study published by Nature in March 2020, for example, Anna Miró-Padilla and colleagues found that n-back training led to decreased activation in the anterior dorsolateral prefrontal cortex, a cerebral change that implies improved neural efficiency and may positively affect untrained tasks that rely on the same cognitive processes. What’s more, these neural changes fully persisted in follow-up tests that were conducted five weeks later.
And in November 2020, in yet another study published by Nature, Tiina Salminen and colleagues found that dual n-back training improves functional connectivity of the right inferior frontal gyrus at rest. I.e., dual n-back training not only affects the task-related neuronal activity, but also neural activation in the resting-state networks of the brain. This is relevant, because resting state functional connectivity is predictive of performance on cognitive tasks in general.
Try It Out for Yourself
If you’re interested in raising your IQ, or staving off age-related cognitive decline, we encourage you to take the N-Back Challenge, available both on iOS and on Android. It’s an n-back app that we’ve built with two main objectives in mind: First, our two founders – both PhDs, one with a focus on neuroscience, the other with a focus on higher education – took pains to ensure that we provide learners with an experience that closely mirrors the design of the scientific studies. This maximizes the probability that, upon completion of the program, you will actually experience the cognitive benefits demonstrated in the research. Second, we try to help you actually get through 20 sessions via a design that’s centered on your commitment to approach the program as a Challenge, with various reward mechanisms to keep you engaged, such as statistics that track your progress, comparisons of your performance against other learners, an opportunity to build up daily “streaks,” and more. This is important, because dual n-back, as you will see, is very exhausting, and it requires a lot of motivation and self-discipline to stick with it. In short: Dual n-back is no fun, but it works!
