Work In Progress - How Much Do We Really Know About The Brain? | Inside The Teenage Brain | FRONTLINE (2024)

What are we learning about the brain's development as a result of new imagingtechnologies, such as functional magnetic resonance imaging?

Fischer: Functional MRI (fMRI) tells us about the location of majorbrain activity during a behavior, including not only in the cortex but alsostructures farther down in the brain. While fMRI gets the most publicity,several other new techniques make equally important contributions. Themagnetoencephalogram (MEG) and the classical electroencephalogram (EEG) givethe best information about brain activity over time as well as connectionsbetween cortical regions. The MEG tells us about brain activity in much thesame way as the EEG, indicating the activity of neural networks in real time;but it gives more information than the EEG about deeper structures. Coherenceanalysis of EEG or MEG tells which parts of the brain are connected to eachother by analyzing similarities in brain activity patterns. Combininginformation from these and other sources provides a much more complete portraitof brain functioning than has ever been possible.

Greenough: The principal news based upon both newer techniques like fMRIand other technologies is that the brain is a very dynamic place and continuesto be so throughout development and even into adulthood. New synapticconnections continue to form between neurons throughout life. Patterns ofmyelination [the process by which brain cells are covered with a fatty whitesubstance called myelin, which aids in the transmission of information betweencells], while perhaps most dynamic from early development through adolescence,continue to change at least into the 4th decade of life. And blood vessels,the brain capillary networks in particular, respond to long-term changes indemand throughout much of adult life. Perhaps most exciting is that at leastsome regions of the brain continue to generate new neurons in adulthood, andthose neurons appear to participate in the learning and memory process.Scientists first made these observations in animals and subsequently confirmedthem in humans.

Thompson: These new imaging techniques provide extremely detailedpictures of the living brain, revealing how it grows and how its functionchanges though the teenage years, often in ways no one suspected.

Before brain imaging was invented, autopsy studies showed that older childrenhad more of a fatty substance, called myelin, on their brain cells. This speedsup the electrical transmission of information between brain cells and isthought to make the brain more efficient as we go through the teen years.Earlier studies also revealed an exuberant growth of connections in the firsttwo years of life, with a slow elimination of connections thereafter.

Now, imaging technologies let us visualize even more remarkable changes in thebrains of children and teens. Using MRI scans, we can watch teenagers' brainschange in miraculous patterns as they grow up. We recently created the firstmaps of brain growth in individual children and teens. To our surprise, anextraordinary wave of tissue growth spread through the brain, from front toback, between the ages of three and 15. Frontal brain circuits, which controlattention, grew fastest from ages three to six. Language systems, which are furtherback in the brain, underwent a rapid growth spurt around the age of 11 to 15,and then drastically shut off in the early teen years. This language systemgrowth is interesting, as it corresponds to the end of a period when we arethought to be most efficient at learning foreign languages. Perhaps the biggestsurprise of all was how much tissue the brain loses in the teen years. Justbefore puberty, children lost up to 50 percent of their brain tissue in their deepmotor nuclei -- these systems control motor skills such as writing, sports, orpiano. This loss moves like a wildfire into the frontal lobes in late teens. Wethink it is a sign of rapid remodeling of brain tissue well into the teens andbeyond.

In short, MRI scans provide the detail necessary to chart brain growth inindividual children, and we are seeing new growth spurts, and surprising lossesof cells much later than originally thought. It is as if a light has now lit upa huge landscape, and researchers are only just beginning to see the landmarksand features for the first time.

Siegel: Imaging techniques have provided a revolutionary new view intohow the activation of neural circuits in the brain give rise to mentalprocesses, such as memory, emotion, decision-making, and reasoning. Thecorrelation of brain structure and function with the more subjective, butequally real, mental processes that define the mind enables us to deepen ourunderstanding of how systems of neurons within the brain may give rise to howsystems of neurons between brains function. This "interpersonal neurobiology"of understanding how the interaction of brain and human relationships shapeswho we are is an exciting possibility in this new era of systems neuroscience.

How much do we know about the relationship between the anatomy or biology ofthe brain and behavior?

Fischer: We know much more because we are only now able to examine manydimensions of brain functioning in thriving human beings. Still, we do not knowvery much!

Key to our understanding is how the brain functions as a system -- for example,how neural networks grow and function across brain regions. Most of the recentadvances in brain science have involved knowledge of the biology of singleneurons and synapses, not knowledge of patterns of connection and other aspectsof the brain as a system. In time the new imaging techniques will helpscientists and educators to understand how brain and behavior work together,but we have a very long way to go.

Greenough: One thing that we know is that changes in the synapticconnections between neurons, whether involving newly-generated neurons in somebrain regions or only pre-existing neurons in others, are a key part of thememory process.

Thompson: Interestingly, a surprising amount is already known. We know alot about how the brain is organized anatomically and functionally. We knowwhich parts are responsible for specific functions, such as spatial memory,emotion, vision, and language. We know a fair amount about how brain cellsdevelop, how they speak to each other, what molecules are involved in learningand memory, and how they may be altered by disease or medication.

In looking at human brain development, several new techniques are now greatlyaccelerating our understanding of brain and behavior. Functional MRI, forexample, is a new type of imaging technique that lets you see how, and where,the brain activates in response to learning new information, recognizing a facerather than just seeing a face, or learning new languages. These techniquesallow you to find out exactly what changes in the brain when some types ofinformation are learned, or when we perform different tasks such as speaking,or when we are ill.

Siegel: We are just beginning to identify how systems in the brain worktogether in an integrated fashion to create complex mental processes. Themind, which can be defined as a process that regulates the flow of energy andinformation, emanates from the activation of neuronal circuits. This flow,however, occurs not only within the skull, but also between two skulls (as in a"relationship"), and among many skulls (as in a family, or as in the Internet).For this reason, it is crucial in understanding the mind and its developmentthat we embrace the exciting findings from brain science while exploring thereality that brain and mind are not the same. Since energy and information canflow beyond the boundaries of the skin-defined self, mind is a process that isbeyond merely brain anatomy and biology. Behavior, and the mental processesthat motivate it, are a product of the interface of the neurophysiologicalprocesses of the body and the interpersonal processes, of relationships,family, community, and the larger culture. These ideas are explored in my bookThe Developing Mind (Siegel, 1999). Recently, we have started aninterdisciplinary research and education program at UCLA called the Center forCulture, Brain, and Development.

What are the most exciting or promising areas of research into braindevelopment and learning and memory -- particularly pertaining toadolescents?

Siegel: The tremendously exciting findings of significant brainreorganization during the adolescent years has enabled us to begin to addresssome very important questions in a new light:

• Why do psychiatric illnesses so often emerge for the first time inadolescence?
• How and why do changes in brain function and structure correlate withadolescent cognitive and behavioral changes?
• Are there ways of examining our cultural approach to adolescence in a newlight given the pruning and re-structuring of brain circuits during the teenyears?

Regarding learning and memory, the relationships among factual andautobiographical memory suggest that we may be well served to have studentsintegrate knowledge of the semantic (factual world) with self-knowledge(autonoesis) for more lasting and better remembered knowledge structures. Thehippocampus has long been known as an important structure for explicit memory.Recent findings indicate that in some traumatized individuals, the hippocampusmay become damaged -- possibly by way of excessive stress hormone, cortisol,secretion. This finding suggests that the legacy of trauma may then createcognitive impairments making school even more stressful for children who haveexperienced various forms of abuse or neglect. Awareness of these findingscan help clinicians, educators, and policymakers to rethink how they approachindividuals who have been victims of trauma.

The prefrontal cortex has an anatomic location that enables it tointegrate a wide array of neural circuits into a functional whole. Thisprocess of integration enables the prefrontal area to play a central role incomplex mental processes that emerge as the child grows. The dorsolateralprefrontal region is crucial for focal attention and working memory. Theventromedial prefrontal regions, also known as the orbitofrontal cortex becauseit sits behind the orbit of the eyes, is a crucial area involved in a widearray of processes such as social cognition (understanding the minds ofothers), attuned communication, self-regulation, response flexibility (takingin data, pausing, reflecting, and coming up with an adaptive, flexibleresponse), and autobiographical memory and self-awareness.

The development of the prefrontal region may be responsive to patterns ofsocial communication during the early years of life, and perhaps across thelife span. Findings from recent studies of the changes in theadolescent brain point to the "off-line" status of this important integrativeregion. These findings may help us to gain insights into why teenagers act theway they so often do. As one of my patients said after doing an action withlittle thought -- "Don't forget, I am a teenager right now!" Action withoutreflection may often be a sign that the prefrontal cortex's response flexibilityfunction is off-duty.

Fischer: Adolescents' brains show major developmental change,which new research is beginning to unravel. Behavioral scientists havedocumented in the last 25 years that adolescents undergo massive changes incognitive and emotional capacities, and that these changes continue at leastthrough early adulthood, well beyond the teen years. Brain scientists are nowdiscovering similar changes in the brain. An essential question is how themajor changes in brain connection and organization during adolescence and earlyadulthood relate to the established changes in cognitive capacities.

New cognitive capacities emerge at 10, 15, 20, and 25 years, in which youngpeople become capable of using abstract concepts skillfully and relating themto each other in successively more complex ways. Younger children cannot useabstractions flexibly but instead reduce them to concrete instances andmemorized definitions. At 9 to 10 years children become able to constructflexible abstract concepts, such as conformity, responsibility, and theoperation of multiplication; but when they try to relate two abstractions toeach other, they muddle them together. At about age 15 they can build flexiblerelations between a pair of abstractions and thus stop muddling them so badly.At age 19 or 20 they can build complex relations among multiple abstractions,and at 25 they can connect systems of abstractions to understand principlesunderlying them. Each of these developments involves the capacity to build anew kind of understanding, but that capacity is evident only in areas whereyoung people work to construct their understanding -- the new abilities do notappear in all skills but only in those where the individual demonstratesoptimal performance. A major challenge for neuroscientists is to understand howthese emerging capacities relate to brain changes.

Thompson: My own view is that we now have an exciting array oftechniques that are beginning to tell us, in exquisite detail, how the braingrows, and what changes to expect in healthy children and teens. We are alsojust beginning to compare these recently discovered brain changes with changesin autistic children, children with learning or communication disorders, andteenagers with emotional or psychiatric disorders.

The imaging techniques have tremendous promise for understanding how theseenigmatic features of development emerge in healthy children and teens.Large-scale studies are now helping us exploit this technology and build abetter picture of how the brain develops. Sometimes they reveal unsuspectedfeatures, such as the wave of brain tissue loss in the teen years. By studyingthis remodeling process, we hope to shed light on how this process might goawry in diseases that can strike in adolescence, such as schizophrenia.

But I think a second revolution in our understanding will come when we begin tobridge these brain imaging techniques with the powerful tools of the "HumanGenome Project." In a recent study, we reported the first maps to visualize howgenes affect brain structure -- in other words, which parts of the brain'shardware do we inherit from our parents, and which parts can change most inresponse to learning experiences and stimulation? A key focus is studyingfamilies of genes that are implicated in building our brains, and learningexperiences that restructure them. As you read this, your brain is remodelingitself, but we know extremely little about what precisely is causing thechanges. By developing new techniques to bridge imaging and genetics, a secondrevolution in our understanding will come. Only then we will go from observingbrain changes in detail to understanding their causes. This in turn is likelyto shed light on how developmental disorders might respond to new therapies,and what is happening in the healthy teenage brain.

What do you think are the difficulties and risks inherent in trying totranslate neuroscience research into public policy for communities or advicefor parents? What are the potential benefits?

Fischer: Ultimately neuroscience research will contribute enormously toour knowledge about raising and educating children, but right now we know toolittle to build public policy or advice on brain findings.

In contrast to neuroscience, cognitive science and developmental science aremore mature, making enormous contributions to knowledge in the last 50 years.Much policy and advice can be based on that research, but neuroscience is tooyoung to provide such specific guidance.

For example, in just the last few years basic "facts" about brain developmenthave been overturned: Scientists believed that no new synapses or neurons couldgrow in adult brains, but recent research has challenged those beliefs,documenting the growth of both new neurons and new synapses in adults.Extensive research is required to understand how brains function and develop,to get beyond our current primitive state of knowledge.

When neuroscience connects to scientific knowledge about cognition anddevelopment, it can be helpful in a global way, supporting the cognitivedevelopmental knowledge; but it cannot provide specific guidance on its own.With the excitement of the remarkable advances in biology and neuroscience inrecent decades, people naturally want to use brain science to inform policy andpractice, but our limited knowledge of the brain places extreme limits on thateffort. There can be no "brain-based education" or "brain-based parenting" atthis early point in the history of neuroscience!

Thompson: So long as research findings are interpreted carefully, thereare enormous benefits to be gained. As we find out more about how the braindevelops, our medical knowledge is enhanced, and the efficacy of new therapiescan be evaluated in developmental disorders. A second goal is to helpunderstand how we can optimally learn throughout life: in childhood, and in theteen years, are there are key times for learning specific skills? Is there abiological basis to support teaching children certain skills, such asmathematics, or foreign languages, at specific times? These are excitingquestions. However, surprisingly little is known on these topics. Programs areemerging to help explore these questions scientifically. A potential danger isthat findings from brain research can be overstretched, or used prematurely, tosupport particular learning aids, or commercial products. Parents shouldevaluate such claims with caution. Nonetheless, answers are likely to come fromeducators, parents and brain researchers working together on these questions,which may have substantial implications for social and educational policy.

Intriguingly, we know a lot more about factors that impair brain development,such as alcohol, drug abuse, and emotional deprivation, than about factors thatpromote healthy development or optimal learning. It is of paramount importancethat we are aware, as a society, of the harmful effects on brain developmentthat result from drug and alcohol abuse in the teenage years, and, in manycountries worldwide, from malnutrition. These are key areas in whichneuroscience research can provide backing, as well as supplementaryinformation, to help guide policies that address these problems.

Siegel: I have been tremendously excited about the translation offindings not just in neuroscience, but in a wide range of academic disciplinesstudying development, such as anthropology, child psychology, linguistics, andsystems theory, for the non-scientific audience. It has been deeply rewardingto first become immersed in these scientific fields, explore their similaritiesand differences, and then find the convergence of findings despite theirdifferences in concepts, research methodologies, and vocabulary. The"consilience" (E.O. Wilson's term from the book of the same name, 1998) offindings enables an integrated view of the mind, brain, and human relationshipsto emerge. I have been amazed at how this interpersonal neurobiology of thedeveloping mind has been useful to clinicians as well as parents, educators,clergy, and public policy makers. In recent publications, I have tried tooffer some practical suggestions as to what the translation and integration ofthese scientific fields can offer.

There are many ways of exploring the implications for policy or education innoting the important connections among memory, emotion, relationships.Experience matters as the mind emerges from how the genetically programmedmaturation of the nervous system responds to ongoing experience. Genes andexperiences shape how neurons become connected to one another. One risk ofover-interpreting the importance of experience can be found in the simplistic and potentially harmful suggestion for early and excessive amounts of sensorystimulation during infancy. Attachment research suggests that infantsthrive not on excessive stimulation, but rather on forms of collaborativecommunication within interpersonal relationships that appear to promoteemotional well-being. This collaborative, contingent form of communication canbe taught to parents. The roots of possible difficulties parents experiencewith this form of communication can also be explored to enhance the nurturingand compassionate connections parents have with their own children. Theintegration of a systems view of neuroscience to understanding and promotingthe development of children and adolescents has huge potential benefits forpolicy and practice.

More Information
For more on the challenges of applying neuroscientific research to publicpolicy, see "The 'Zero to Three' Debate"

Greenough: The results of neuroscience research cannot be translatedinto policy by itself. We have many sources of information regarding brain andbehavioral development and learning. The best context for policy development isa team of individuals that collectively has expertise in child and adolescentdevelopment (especially developmental psychology), education, medicine (e.g.,child psychiatry) and neuroscience. Working together to interpret the researchand formulate policies that reflect the fullest possible knowledge of thedevelopment process, reasoned and valid policies can be proposed. A volumethat comprises such an interdisciplinary report is "From Neurons toNeighborhoods: The Science of Early Childhood Development" published by theNational Academy of Sciences. The potential benefits of policies that benefitor optimize human development are enormous, ranging from the economic effectsof having a vastly more effective workforce to the societal and medical effectsof a population that is as a whole better adapted to the demands of the 21stcentury lifestyle.