Saturday, October 01, 2005

A Young Mind in a Growing Brain

Building a Bridge Between Brain Science and Education

By: Jay N. Giedd, M.D.

In his widely quoted 1997 article “Education and Neuroscience: A Bridge Too Far?” John Bruer argued that, despite substantial progress in brain research, trying to use its discoveries to shape education policy is both uninformative and misleading. Two new books by prominent scientists, The Learning Brain and A Young Mind in a Growing Brain, take on the formidable challenge of beginning to build this bridge by linking advances in our understanding of the biology of brain maturation to phenomena in other domains, namely education and psychological development. In our era, the term “brain-based” education has been used in many books and has come to encompass many teaching approaches which, in fact, have little basis in brain science. Thus, it is refreshing to see a more rigorous approach to this important frontier. 


rev_v7n4giedd_4The idea for A Young Mind in a Growing Brain was conceived in 1993 when the authors, Harvard University developmental psychologist Jerome Kagan, Ph.D., and Swiss pediatrician Norbert Herschkowitz, M.D., met and recognized the complementary nature of their respective training and personal and professional experiences with infants and children. The fruitfulness of the initial interactions led to an ongoing collaboration. In this book, they integrate our understanding of developmental neurobiology with advances in developmental psychology. 

The intended audience is neuroscientists, psychologists, psychiatrists, pediatricians, and their students. Although parents and teachers may enjoy many aspects of the book, readers outside the field of neuroscience are likely to find the level of biological description daunting. The book is organized into five age categories: prenatal, birth to 6 months, 7 to 12 months, 1 to 2 years, and 2 to 8 years. In each category, psychological phenomena occurring widely across cultures in typically developing children are discussed in relation to simultaneously occurring biological changes. 

For example, between birth and six months, connections formed between the cortex and the spinal motor centers lead to a loss of brain stem reflexes. A spurt of differentiation of dendrite gyrus mossy cells in the hippocampus, a part of the brain associated with memory, allows the formation of what Kagan calls schemata, meaning psychological representations that emerge when an event triggers neuronal activity. Between 7 and 12 months, a growth spurt in the prefrontal cortex underlies the emergence of working memory (the ability to draw on previously formed schemata and relate them to the present event). Maturing of parts of the brain called Wernicke’s and Broca’s areas, between one and two years, permits the acquisition of language. Between two and eight years, with increasingly greater connectivity between brain components, a wide array of capabilities appears, including improved abilities to integrate past and present with future goals. Commenting on development overall, the authors note that “Nature’s plan is, first, to grow the separate parts of the brain, and then to link the components in sets of reciprocal relations.” 


At all of these stages, the physical properties of the maturing brain constrain what is psychologically possible. Biological maturation is always a necessary, but not a sufficient, condition of psychological development, because certain stimuli from the environment are also always required for the biological systems to be fully realized. 

The quest to understand this dynamic relationship between brain maturation and environment in shaping psychological development drives much of current neuroscience research. A Young Mind in a Growing Brain abounds with examples of this relationship. Some psychological developments, such as self-awareness, seem to occur as qualitative leaps; others arrive by more slowly accumulating changes. For example, working memory capacity and the ability to inhibit behaviors improve throughout childhood and adolescence. 

The book concludes with a strong chapter in which the authors reflect on the broadest implications of their material. Some readers will disagree, but most will find thought provoking the section describing the nine properties that distinguish humans from other primates. Four of these properties are uniquely human (inferring thoughts and feelings of others, symbolic language, moral sense, and conscious awareness); the other five are enhanced in humans (working memory, retrieval of past events, future-thinking, inhibition, and attraction to the unfamiliar). 

The authors note that just four extra cycles of cell division in the developing brain—requiring only 72 hours—could make the difference between the 100 billion neurons of humans and the 10 billion neurons of the chimpanzee. They argue compellingly that all our uniquely human or enhanced abilities may reflect the greater size of our prefrontal cortex and the degree of its connectivity with other brain structures. The prefrontal cortex is the most preferentially larger brain area in humans as compared with apes, has the greatest density of dendritic spines, and maintains synaptic pruning longer than other brain areas. All of this bolsters their assertion that the prefrontal cortex is primary in distinguishing human psychological properties. 


Throughout A Young Mind in a Growing Brain, Kagan and Herschkowitz emphasize the limitations of current research methods and caution readers about leaping to a single, unitary interpretation of a given set of facts. 

Consider one example. Much of the literature about assessing an infant’s knowledge is based on observing and measuring how the infant orients itself to an event. Infants usually respond to novel environmental stimuli differently from stimuli to which they have become accustomed. With training, infants can be taught to look in a certain direction when they hear a novel sound. Then, if those infants turn toward a sound, we infer that they detected that the sound was novel. But if an infant does not turn toward a sound, it does not necessarily mean that he did not detect the novelty of the sound. Many things may influence the infant’s reaction: the physical properties of the event, the relation to previously acquired schemata, and pleasure/pain principles. 

In fact, electrical recordings of brain activity by evoked response potentials (ERP) may indicate that the infant’s brain is detecting novelty, but we still may observe no orientating or other behavior. Likewise, ERP changes in adults resulting from hearing a sentence ending with an unexpected word (“the museum walls were lined with cabbage”) were often interpreted as registering the brain’s representation of surprise at the semantic inconsistency—until it was discovered that the ERP pattern occurs even when adults are sleeping and have no conscious reaction to the discrepancy. 

The authors also emphasize that imprecise use of terminology, such as “surprise,” to denote a pattern of neural activity, is more than a trivial annoyance; it can be a serious impediment to understanding and progress in the field. Names of popular emotional concepts borrowed from an ancient vocabulary do not have the precision required for accurate understanding of experimental outcomes. For example, in common usage the word “reward” means receiving something of value for a job well done. In the 20th century, behavioral scientists gave the word a technical denotation by defining reward as any event that increased the probability of a response. The problem is that scientists have learned that many events that meet the technical, behavioral definition of reward do not share a common brain state. Sucrose is “rewarding” to rats, according to the behavioral definition of increasing frequency of response to obtain more, and it increases dopamine in the prefrontal cortex. But, although sucrose plus chocolate is also “rewarding” in the behavioral sense, it increases dopamine in two parts of the brain: the prefrontal cortex and the nucleus accumbens. Applying the same term to characterize these different neuronal patterns leads to imprecise interpretation. Scientists need a new vocabulary to reflect these various levels of psychological functions that can be measured using new research technology. 

Readers interested in this topic will likely enjoy the classic 1927 lecture by Ivan Pavlov “Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex” in which he eloquently and forcefully lays the groundwork for much of the current debate on the relationship between physiology and psychology. 


Another caveat in interpretation raised by Kagan and Herschkowitz concerns the localization of cerebral functions. As with the issue of terminology, much of the confusion stems from lack of clarity about what level of complexity and hierarchical organization is being discussed. Clearly, some degree of localization is present in the brain. The charge of clinical neurology is to “locate the lesion,” and thousands of peer-reviewed papers are published each year about, in some way, the localization of cerebral function. Some systems, such as the auditory cortex’s response to different sound frequencies, are precisely localized, with adjacent frequencies activating adjacent brain areas. But recent reports interpreted as claiming to have found the cerebral “location” of intelligence or humor or morality belie the emergent nature of these complex properties and the concept of distributed neural networks. 

It may be useful to think of the different brain areas like letters of the alphabet. A given letter may be part of many different words, and a given word may be part of many different sentences. Primary functions —such as detection of the frequency of an auditory tone—may be at the letter level, localized to a small area. Most processes of interest to psychologists, however, are at least at the level of words, and many are at the level of sentences or paragraphs. To talk about a single location of these more complex psychological constructs is misleading and hinders progress in research. 

Sorting out which functions are localized is not a trivial process. Some cortical areas may be used not so much for a specific process as for a type of processing. For example, it is not clear that even areas that experimenters and observers have linked with language functions for years (for example, Wernicke’s or Broca’s area) are in fact dedicated to language. They may be specialized for a more general capacity to process rapidly occurring sequential information, of which speech is only one example. Likewise, the fusiform gyrus was widely described as the brain’s “face” area because it is shown to be activated when processing images of faces. Subsequent work, however, has shown that the area is also activated when processing the internal features of automobiles and other objects. 

Another nuance of localization is the brain’s enormous plasticity, especially for dealing with injuries or other trauma occurring early in life. Thus, in blind people reading Braille, so-called “visual areas” of the brain are activated, even though typical somatosensory cortex is toward the middle of the brain and the visual cortex is several centimeters away in the posterior portion of the brain. Children with hydrocephalus who have had large portions of their cerebral cortex damaged in utero also demonstrate the brain’s remarkable ability to relocate functions. 


Like Frith and Blakemore in The Learning Brain, Kagan and Herschkowitz masterfully meet their stated goal of integrating our current understanding of psychological growth with our current understanding of brain development. Particularly admirable is the degree to which all the authors point out limitations of such integration and offer multiple interpretations of the data. Through it all, they firmly establish the principle that emergent psychological functions depend on the maturation of the underlying biology. Future progress in exploring the nexus between psychology and physiology will benefit from developing novel hypotheses from one field that can be tested in the other. Knowledge at the interface of the two disciplines can be complementary and can lead to stronger experimental designs. 

Echoing the sentiments of John Bruer noted in the opening sentence of this review: To date, the astounding advances in our understanding of brain science have had little practical impact on our educational systems—though perhaps a greater, if still minor, impact on the field of psychology. The canyon between brain science and these other disciplines calls for a bridge of monumental proportions. These two books have not built it, but they have made a good start by casting their lines across. They have established contact. There is a long way yet to go before we can say we are connected, but the benefits of applying our understanding of the brain to improving the human condition make this a bridge worth building. 


From A Young Mind in a Growing Brain by Jerome Kagan and Norbert Herschkowitz. © 2005 Jerome Kagan and Norbert Herschkowitz. Reprinted with permission of Lawrence Erlbaum Associates. 

Historians are distinguished by the conceptual frame they impose on their evidence. Some prefer the journalist’s sequential narration of events; others favor a skeptical, sardonic, or optimistic construction of the facts; still others celebrate an aesthetically pleasing coherence of cause-effect relations among events that were independent. We place ourselves to the right of the skeptic and to the left of the Platonist whose ideas shimmer with the gleam of perfect understanding. A wrinkled guru who knows how brains and minds grow might shake his head after reading our arguments and mutter that all we have done is to describe a few approximately temporal correspondences between changes in brain and psychological functions and suggested, with insufficient caution, that the appearance of the latter required the former, although they would not appear unless the proper experiences had intervened. 

The history of science is littered with examples of this easy error. Many were certain that foul air was the villainous culprit when Europe was struck with the plague over 6 centuries ago; others were equally sure that a Jewish curse caused the epidemic. Sixteenth-century naturalists believed that a burned log lost its original weight because it released its store of phlogiston. And only 50 years ago, child psychiatrists were convinced that a mother’s rejecting, aloof attitude could cause her child to show the compromised social and language functions characteristic of autism. 

We have reminded readers repeatedly that brain maturation only constrains the earliest age of appearance of select psychological functions; it does not guarantee the actualization of those functions...The developing brain also modulates the emotions that require new cognitive abilities.

About Cerebrum

Bill Glovin, editor
Carolyn Asbury, Ph.D., consultant

Scientific Advisory Board
Joseph T. Coyle, M.D., Harvard Medical School
Kay Redfield Jamison, Ph.D., The Johns Hopkins University School of Medicine
Pierre J. Magistretti, M.D., Ph.D., University of Lausanne Medical School and Hospital
Helen Mayberg, M.D., Icahn School of Medicine at Mount Sinai 
Bruce S. McEwen, Ph.D., The Rockefeller University
Donald Price, M.D., The Johns Hopkins University School of Medicine
Charles Zorumski, M.D., Washington University School of Medicine

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