6 BRAIN TRAINING

The term “brain training” usually refers to computer games designed to improve mental functions such as attention and working memory. These games are purported to improve such functions—and overall brain health—by exercising the organ, in the same way that physical activity helps to maintain the health of the body.

Today, brain training is a multimillion dollar industry, and there are dozens of companies selling computer games, gadgets, and smartphone applications. Many of these products are targeted toward the aging and elderly, and are purported to improve overall brain health and even reduce the risk of developing Alzheimer’s disease and other forms of dementia. Currently, however, there is very little evidence that brain training products lead to what psychologists call transfer effects: they do lead to significant improvements in the mental abilities needed to perform well at the game, as would be expected, but it is still unclear whether they also improve other, unrelated cognitive functions.¹

Currently, there is very little evidence that brain training products lead to what psychologists call transfer effects.

In October 2014, a large group of eminent researchers issued a joint statement on the subject. “We object to the claim that brain games offer consumers a scientifically grounded avenue to reduce or reverse cognitive decline when there is no compelling scientific evidence to date that they do,” they wrote. “The promise of a magic bullet detracts from the best evidence to date, which is that cognitive health in old age reflects the long-term effects of healthy, engaged lifestyles. In [our] judgement, exaggerated and misleading claims exploit the anxiety of older adults about impending cognitive decline. We encourage continued careful research and validation in this field.”² About one year later, the San Francisco-based brain training company Lumosity was ordered by the U.S. Federal Trade Commission to pay a $2 million settlement for deceiving customers with unfounded claims about the benefits of their products.³

As we have seen, though, the brain is continuously being shaped by our experiences, and there is now plenty of evidence that other types of brain training have significant effects on the organ. Animal research has provided important information about the cellular mechanisms of plasticity induced by training. For example, training rats to make fine-grained time judgments expands the bandwidth sensitivity of auditory neurons, whereas training owl monkeys on a touch discrimination task shrinks the receptive fields of neurons in the primary somatosensory cortex, the part of the brain that processes touch information.

Lasting changes are far harder to study in animals and, until relatively recently, in humans, too. In the past 20 years or so, however, the use of neuroimaging technologies has become widespread, and the number of studies using these methods to investigate the neural consequences of long-term training is growing. With these methods at their disposal, researchers have shown that learning a second language is associated with various anatomical changes in the brain. Similarly, some people spend years or decades acquiring other types of knowledge, skills, or expertise. Such rigorous, long-term training also leads to long-lasting changes in both the structure and function of the brain. Professional athletes, musicians, and the like, are therefore a fascinating natural laboratory for the study of experience-dependent neuroplasticity.⁴

Language Learning

A pioneering 2004 study used voxel-based morphometry to examine the brains of bilingual Europeans and compare them to those of monolinguals. This revealed that bilingualism is associated with increased gray matter density in the left inferior parietal lobule, a region of the brain that has been implicated in a number of important language-related functions, such as phonological working memory (or memory for language sounds), lexical learning, and the integration of information from diverse sources, and so the volume increase may reflect acquisition of second-language vocabulary.

The researchers found that the effect was bigger in early than in late learners: participants who started learning a second European language before the age of 5 exhibited larger volume increases than those who learned later. The extent of the change was also related to individuals’ ability for language learning, such that those who were more proficient at acquiring their second language showed greater increases in gray matter volume than those who found it more difficult.⁵

Subsequent studies have confirmed these initial findings and have also demonstrated that learning a second language is associated with other kinds of anatomical changes, including changes in cortical thickness in brain areas linked to language, as well as changes in the architecture of the white matter tracts that interconnect them. Even short-term language training alters brain structure: various studies show that college students and military interpreters who enrolled in intensive three-month language courses exhibited brain differences compared to controls who had not.

The anatomical changes associated with language learning appear to be reversible, though. One brain scanning study found that adult Japanese speakers who took a six-week English-language course had increased gray matter density, compared to controls, in certain language regions of the brain. Follow-up scans performed a year later revealed even bigger increases in those who had kept up their language practice. In those who had stopped, however, gray matter density in the affected brain regions had returned to pre-training levels.⁶

Unlike commercially available brain training products, language learning does appear to have transfer effects, and evidence that lifelong bilingualism confers certain advantages is beginning to emerge. Bilingualism requires switching between languages and selecting the correct vocabulary, among other tasks that exercise so-called executive functions such as reasoning, task switching, and problem solving. Furthermore, learning a second language apparently has neuroprotective effects; thus it may reduce the risk of Alzheimer’s disease and other neurodegenerative conditions, even when it takes place in later life, by increasing “cognitive reserve”— a somewhat vague term that refers to the mind’s resistance to brain damage.⁷

Musical and Athletic Training

Early neuroimaging studies revealed that long-term training regimes are associated with differences in both gray and white matter. Thus, classical musicians who started training before the age of 7 have a larger corpus callosum than those who started their training later and nonmusical controls. This huge bundle of nerve fibers contains fibers that cross from one side of the brain to the other and coordinates the activity of the limbs.⁸ And the dexterity required of professional violinists is associated with extensive reorganization of finger representation in the primary somatosensory cortex. The representation of the fingers of the left hand in the somatosensory cortex was larger in the musicians than in healthy nonmusical controls, and the difference was more pronounced in those who had started their training at an earlier age. Cortical representation of the right hand, with which string instrument players hold the bow, remained unchanged.⁹

More recent studies provide similar findings. Using a neuroimaging technique called voxel-based morphometry, researchers have shown that professional keyboard players have larger gray matter volumes in motor, auditory, and visuospatial brain regions compared to amateur musicians and nonmusical controls, with the extent of the change again correlated to the length of time as a musician.¹⁰

Others have used diffusion tensor imaging (DTI) to show that piano practice alters the brain’s white matter tracts, and that the effects depend on the age period during which the training took place. The changes are seen in the corpus callosum and in fibers that descend from the sensory and motor cortices, and were most pronounced in professional concert pianists who began training before the age of 7.¹¹ Similarly, karate black belts exhibit significantly larger white matter tracts in the motor cortex and cerebellum than novices and controls, giving them superior motor coordination and enabling them to pack more power into their punches and kicks.¹²

Most of these studies involved recruiting small groups of experts or professionals and comparing the structure or function of their brains with those of amateurs or novices at a single point in time. This cross-sectional experimental design cannot conclusively establish whether any observed differences are the result of training, or whether they reflect anatomical and genetic differences that were present at birth—it may be the case that certain people are born with brains that predispose them to acquiring a particular skill or expertise more easily than others. Distinguishing between these possibilities would require longitudinal studies in which members of each group have their brains scanned repeatedly over a period of months or years.

The few longitudinal MRI studies that have been performed to date do suggest that at least some of the observed differences are indeed due to training. For example, learning to juggle over a period of several months leads to increased gray matter density in the occipitotemporal cortex, which contains motion-sensitive neurons.¹³ It also enlarges the white matter tracts beneath the intraparietal sulcus, which contains brain regions that integrate perceptual and motor information and are critical for controlling and coordinating arm and eye movements.¹⁴

The Knowledge

A series of studies performed on London taxi drivers over the past 15 years provides yet more evidence that mental training can indeed induce anatomical changes to the brain. To qualify as a licensed London taxi driver, trainees undergo years of comprehensive memory training to learn the labyrinthine layout of some 26,000 streets within a six-mile radius of Charing Cross station, the location of thousands of landmarks, and also the quickest way to navigate between any two points in the city.

Prospective taxi drivers typically spend three to four years studying maps and driving around the city, in order to acquire “the Knowledge” of London’s streets. During this time, they also take a set of stringent examinations designed to test their spatial learning of each city district, and are allowed a limited number of attempts at each before progressing on to the next. Only after successfully completing all of these examinations can they qualify and obtain a license to operate one of London’s famous black taxis, and approximately half of those who begin the training fail their examinations or drop out at some point.

In 2000, researchers at University College London published a study showing that gray matter density in the posterior hippocampus is significantly larger in qualified London taxi drivers than in controls. This brain structure is known to be involved in spatial navigation, and the study also showed that its size was closely correlated with the amount of time spent as a taxi driver—the more experienced the driver, the larger was their posterior hippocampus.¹⁵

This study was also a cross-sectional one, so the researchers could not rule out the possibility that the differences they had observed were due to preexisting anatomical differences, but they went on to perform several follow-up studies that confirmed that the changes were indeed due to the prolonged and rigorous training regime. First, they scanned the brains of some London bus drivers, who also navigate London’s streets, along far simpler, predetermined routes, revealing that gray matter density in their hippocampi is not significantly different from that of controls.

Next, the researchers carried out a longitudinal study in which they repeatedly scanned the brains of trainee taxi drivers as they underwent training. Of the 79 trainees enrolled in the study, 39 went on to qualify as taxi drivers, and 20 failed the training but agreed to return for brain scanning nevertheless. Those who qualified exhibited the same increases in gray matter density, but the hippocampi of those who had failed looked no different from those of subjects in the control group.¹⁶

Together, these studies show that the comprehensive memory training required to successfully complete “the Knowledge” induces specific changes in brain anatomy. Just as weightlifting leads to an enlargement of muscle tissue, so too can mental training expand corresponding parts of the brain. This comes at a price, however—qualified London taxi drivers appear to be worse at acquiring new visuospatial information than others, and some researchers suspect that their increasing use of satellite navigation devices could lead to a gradual deterioration of the hippocampus.

Thus, the brain is a highly dynamic organ that adapts to its user’s demands. Intensive training alters the brain in such a way that it begins to execute the appropriate functions more efficiently. Musical and athletic training enhance the execution of the complex sequences of movements needed, and trainees acquiring “the Knowledge” learn how to organize huge amounts of spatial information and then use it effectively. In this way, training optimizes the brain areas and neural pathways involved in performing a given task; as a result, the individual’s performance on that task improves, and the task eventually becomes automatized and effortless.

The available data suggest that gaining expertise in any domain requires at least four hours of training per day for approximately 10 years. Remarkably, there is also compelling evidence that motor imagery—that is, visualizing certain movements in the mind’s eye—can also enhance the learning and execution of certain skills. Thus, imagined movements appear to be equivalent to those that are actually performed, and merely “going through the motions” in one’s mind can lead to the same kind of plastic changes in the brain.¹⁷

Training optimizes the brain areas and neural pathways involved in performing a given task; as a result, the individual’s performance on that task improves, and the task eventually becomes automatized and effortless.

Of Mice and Men

Neuroimaging studies have provided a wealth of information about how prolonged intensive mental training alters the brain, but they tell us nothing about the molecular and cellular mechanisms underlying the observed changes. Experiments performed on rodents show that rigorous training on motor tasks can exert various cellular effects, such as the sprouting and pruning of new dendritic spines and axonal branches. It is impossible to observe equivalent processes in humans, however, both because the resolution of current neuroimaging technologies is far below that needed to visualize them and because the techniques used in mice and rats cannot be applied to studying the human brain.

Increases in gray matter density and volume could be explained by adult neurogenesis. That explanation is particularly attractive in the case of London taxi drivers, since the hippocampus is currently the only region of the human brain that is known to continue generating new neurons throughout life (see chapter 5). But the increases can also be explained by the formation of new dendritic spines and synapses and the sprouting of new axon branches. Increases in the number of glial cells, or the formation of new blood vessels to supply new structures with blood, could also increase gray matter density.

Likewise, changes in white matter structure could be due to various mechanisms, such as the addition and removal of myelin from axons, or alterations in myelin thickness or in the spacing between nodes of Ranvier, all of which would alter the conducting properties of a neuron. Although diffusion tensor imaging is sensitive to variations in myelin, it is not yet sensitive enough to distinguish between these mechanisms.¹⁸

Neuroimaging data can sometimes seem counterintuitive and are often difficult to interpret. One recent study compared brain activity of professional soccer players and swimmers while they performed identical foot movements, and found that the soccer players exhibited less activity in the motor cortical area corresponding to the foot than did the swimmers. The researchers interpreted this as meaning that years of training enable the soccer players to control their foot movements efficiently while also conserving their neural resources.¹⁹

Clearly, the brain is highly flexible, but we are only just beginning to understand the many ways in which it can adapt to the demands placed upon it. Technological advances will allow for increasingly sophisticated ways of imaging the brain, and will surely deepen our knowledge of how different types of training affect brain structure and function.