FRONTLINE asked four prominent psychologists and neuroscientists to answer some
questions about the extent of our knowledge of the brain and its
development -- connections between the anatomy of the brain and behavior, new
directions for research, and how close we are to translating new findings into
advice for parents or educators.
+ What are we learning about the brain's development as a result of new imaging
technologies such as functional magnetic resonance imaging?
+ How much do we know about the relationship between the anatomy or biology of
the brain and behavior?
+ What are the most exciting or promising areas of research into brain
development and learning and memory -- particularly pertaining to
+ What do you think are the difficulties and risks inherent in trying to
translate neuroscience research into public policy for communities or advice
for parents? What are the potential benefits?
What are we learning about the brain's development as a result of new imaging
technologies, such as functional magnetic resonance imaging?
Fischer: Functional MRI (fMRI) tells us about the location of major
brain activity during a behavior, including not only in the cortex but also
structures farther down in the brain. While fMRI gets the most publicity,
several other new techniques make equally important contributions. The
magnetoencephalogram (MEG) and the classical electroencephalogram (EEG) give
the best information about brain activity over time as well as connections
between cortical regions. The MEG tells us about brain activity in much the
same way as the EEG, indicating the activity of neural networks in real time;
but it gives more information than the EEG about deeper structures. Coherence
analysis of EEG or MEG tells which parts of the brain are connected to each
other by analyzing similarities in brain activity patterns. Combining
information from these and other sources provides a much more complete portrait
of brain functioning than has ever been possible.
Greenough: The principal news based upon both newer techniques like fMRI
and other technologies is that the brain is a very dynamic place and continues
to be so throughout development and even into adulthood. New synaptic
connections continue to form between neurons throughout life. Patterns of
myelination [the process by which brain cells are covered with a fatty white
substance called myelin, which aids in the transmission of information between
cells], 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 in
demand throughout much of adult life. Perhaps most exciting is that at least
some regions of the brain continue to generate new neurons in adulthood, and
those neurons appear to participate in the learning and memory process.
Scientists first made these observations in animals and subsequently confirmed
them in humans.
Thompson: These new imaging techniques provide extremely detailed
pictures of the living brain, revealing how it grows and how its function
changes though the teenage years, often in ways no one suspected.
Before brain imaging was invented, autopsy studies showed that older children
had more of a fatty substance, called myelin, on their brain cells. This speeds
up the electrical transmission of information between brain cells and is
thought to make the brain more efficient as we go through the teen years.
Earlier studies also revealed an exuberant growth of connections in the first
two years of life, with a slow elimination of connections thereafter.
Now, imaging technologies let us visualize even more remarkable changes in the
brains of children and teens. Using MRI scans, we can watch teenagers' brains
change in miraculous patterns as they grow up. We recently created the first
maps of brain growth in individual children and teens. To our surprise, an
extraordinary wave of tissue growth spread through the brain, from front to
back, between the ages of three and 15. Frontal brain circuits, which control
attention, grew fastest from ages three to six. Language systems, which are further
back 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 system
growth is interesting, as it corresponds to the end of a period when we are
thought to be most efficient at learning foreign languages. Perhaps the biggest
surprise of all was how much tissue the brain loses in the teen years. Just
before puberty, children lost up to 50 percent of their brain tissue in their deep
motor nuclei -- these systems control motor skills such as writing, sports, or
piano. This loss moves like a wildfire into the frontal lobes in late teens. We
think it is a sign of rapid remodeling of brain tissue well into the teens and
In short, MRI scans provide the detail necessary to chart brain growth in
individual children, and we are seeing new growth spurts, and surprising losses
of cells much later than originally thought. It is as if a light has now lit up
a huge landscape, and researchers are only just beginning to see the landmarks
and features for the first time.
Siegel: Imaging techniques have provided a revolutionary new view into
how the activation of neural circuits in the brain give rise to mental
processes, such as memory, emotion, decision-making, and reasoning. The
correlation of brain structure and function with the more subjective, but
equally real, mental processes that define the mind enables us to deepen our
understanding of how systems of neurons within the brain may give rise to how
systems of neurons between brains function. This "interpersonal neurobiology"
of understanding how the interaction of brain and human relationships shapes
who 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 of
the brain and behavior?
Fischer: We know much more because we are only now able to examine many
dimensions of brain functioning in thriving human beings. Still, we do not know
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 recent
advances in brain science have involved knowledge of the biology of single
neurons and synapses, not knowledge of patterns of connection and other aspects
of the brain as a system. In time the new imaging techniques will help
scientists 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 synaptic
connections between neurons, whether involving newly-generated neurons in some
brain regions or only pre-existing neurons in others, are a key part of the
Thompson: Interestingly, a surprising amount is already known. We know a
lot about how the brain is organized anatomically and functionally. We know
which parts are responsible for specific functions, such as spatial memory,
emotion, vision, and language. We know a fair amount about how brain cells
develop, how they speak to each other, what molecules are involved in learning
and memory, and how they may be altered by disease or medication.
In looking at human brain development, several new techniques are now greatly
accelerating our understanding of brain and behavior. Functional MRI, for
example, 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 face
rather than just seeing a face, or learning new languages. These techniques
allow you to find out exactly what changes in the brain when some types of
information 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 work
together in an integrated fashion to create complex mental processes. The
mind, which can be defined as a process that regulates the flow of energy and
information, 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 development
that we embrace the exciting findings from brain science while exploring the
reality that brain and mind are not the same. Since energy and information can
flow beyond the boundaries of the skin-defined self, mind is a process that is
beyond merely brain anatomy and biology. Behavior, and the mental processes
that motivate it, are a product of the interface of the neurophysiological
processes of the body and the interpersonal processes, of relationships,
family, community, and the larger culture. These ideas are explored in my book
The Developing Mind (Siegel, 1999). Recently, we have started an
interdisciplinary research and education program at UCLA called the Center for
Culture, Brain, and Development.
What are the most exciting or promising areas of research into brain
development and learning and memory -- particularly pertaining to
Siegel: The tremendously exciting findings of significant brain
reorganization during the adolescent years has enabled us to begin to address
some very important questions in a new light:
- Why do psychiatric illnesses so often emerge for the first time in
- How and why do changes in brain function and structure correlate with
adolescent cognitive and behavioral changes?
- Are there ways of examining our cultural approach to adolescence in a new
light given the pruning and re-structuring of brain circuits during the teen
Regarding learning and memory, the relationships among factual and
autobiographical memory suggest that we may be well served to have students
integrate knowledge of the semantic (factual world) with self-knowledge
(autonoesis) for more lasting and better remembered knowledge structures. The
hippocampus has long been known as an important structure for explicit memory.
Recent findings indicate that in some traumatized individuals, the hippocampus
may become damaged -- possibly by way of excessive stress hormone, cortisol,
secretion. This finding suggests that the legacy of trauma may then create
cognitive impairments making school even more stressful for children who have
experienced various forms of abuse or neglect. Awareness of these findings
can help clinicians, educators, and policymakers to rethink how they approach
individuals who have been victims of trauma.
Kurt W. Fischer
Fischer is Charles Bigelow Professor of Education and Human Development and
director of the Mind, Brain, & Education Program at the Harvard Graduate
School of Education. His work focuses on the organization of behavior and the ways it changes,
especially cognitive development, social behavior, emotions, and brain bases.
William T. Greenough
Swanlund Professor of Psychology, Psychiatry, and Cell and Structural Biology
and director of the Center for Advanced Study at the University of Illinois,
Greenough is an authority on the effects of experience and learning on the
structure and function of the mammalian brain. His work on the effects of
enriched-environment rearing on brain structure in the 1970s and early
1980s revolutionized thinking about brain plasticity, and serves as the primary
basis for the current belief that memory involves the formation and
modification of the synapses through which nerve cells communicate.
Siegel, the author of The Developing Mind: How Relationships and the
Brain Interact to Shape Who We Are (Guilford, 1999), is an associate clinical professor at UCLA's School of Medicine. He also is co-investigator at UCLA's Center for Culture, Brain, and Development, and director of the Center for Human Development in Los Angeles.
Thompson is assistant professor of neurology at UCLA's Lab of Neuro-Imaging &
Brain Mapping Division. He worked with Dr. Jay Giedd on the research into the changing frontal cortex of the adolescent brain. His research also
encompasses new brain-mapping technologies, studies of Alzheimer's and
schizophrenia, and neuro-oncology.
The prefrontal cortex has an anatomic location that enables it to
integrate a wide array of neural circuits into a functional whole. This
process of integration enables the prefrontal area to play a central role in
complex mental processes that emerge as the child grows. The dorsolateral
prefrontal region is crucial for focal attention and working memory. The
ventromedial prefrontal regions, also known as the orbitofrontal cortex because
it sits behind the orbit of the eyes, is a crucial area involved in a wide
array of processes such as social cognition (understanding the minds of
others), attuned communication, self-regulation, response flexibility (taking
in data, pausing, reflecting, and coming up with an adaptive, flexible
response), and autobiographical memory and self-awareness.
The development of the prefrontal region may be responsive to patterns of
social communication during the early years of life, and perhaps across the
life span. Findings from recent studies of the changes in the
adolescent brain point to the "off-line" status of this important integrative
region. These findings may help us to gain insights into why teenagers act the
way they so often do. As one of my patients said after doing an action with
little thought -- "Don't forget, I am a teenager right now!" Action without
reflection may often be a sign that the prefrontal cortex's response flexibility
function is off-duty.
Fischer: Adolescents' brains show major developmental change,
which new research is beginning to unravel. Behavioral scientists have
documented in the last 25 years that adolescents undergo massive changes in
cognitive and emotional capacities, and that these changes continue at least
through early adulthood, well beyond the teen years. Brain scientists are now
discovering similar changes in the brain. An essential question is how the
major changes in brain connection and organization during adolescence and early
adulthood relate to the established changes in cognitive capacities.
New cognitive capacities emerge at 10, 15, 20, and 25 years, in which young
people become capable of using abstract concepts skillfully and relating them
to each other in successively more complex ways. Younger children cannot use
abstractions flexibly but instead reduce them to concrete instances and
memorized definitions. At 9 to 10 years children become able to construct
flexible abstract concepts, such as conformity, responsibility, and the
operation of multiplication; but when they try to relate two abstractions to
each other, they muddle them together. At about age 15 they can build flexible
relations 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 principles
underlying them. Each of these developments involves the capacity to build a
new kind of understanding, but that capacity is evident only in areas where
young people work to construct their understanding -- the new abilities do not
appear in all skills but only in those where the individual demonstrates
optimal performance. A major challenge for neuroscientists is to understand how
these emerging capacities relate to brain changes.
Thompson: My own view is that we now have an exciting array of
techniques that are beginning to tell us, in exquisite detail, how the brain
grows, and what changes to expect in healthy children and teens. We are also
just beginning to compare these recently discovered brain changes with changes
in autistic children, children with learning or communication disorders, and
teenagers with emotional or psychiatric disorders.
The imaging techniques have tremendous promise for understanding how these
enigmatic features of development emerge in healthy children and teens.
Large-scale studies are now helping us exploit this technology and build a
better picture of how the brain develops. Sometimes they reveal unsuspected
features, such as the wave of brain tissue loss in the teen years. By studying
this remodeling process, we hope to shed light on how this process might go
awry in diseases that can strike in adolescence, such as schizophrenia.
But I think a second revolution in our understanding will come when we begin to
bridge these brain imaging techniques with the powerful tools of the "Human
Genome Project." In a recent study, we reported the first maps to visualize how
genes affect brain structure -- in other words, which parts of the brain's
hardware do we inherit from our parents, and which parts can change most in
response to learning experiences and stimulation? A key focus is studying
families of genes that are implicated in building our brains, and learning
experiences that restructure them. As you read this, your brain is remodeling
itself, but we know extremely little about what precisely is causing the
changes. By developing new techniques to bridge imaging and genetics, a second
revolution in our understanding will come. Only then we will go from observing
brain changes in detail to understanding their causes. This in turn is likely
to 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 to
translate neuroscience research into public policy for communities or advice
for parents? What are the potential benefits?
Fischer: Ultimately neuroscience research will contribute enormously to
our knowledge about raising and educating children, but right now we know too
little to build public policy or advice on brain findings.
In contrast to neuroscience, cognitive science and developmental science are
more mature, making enormous contributions to knowledge in the last 50 years.
Much policy and advice can be based on that research, but neuroscience is too
young to provide such specific guidance.
For example, in just the last few years basic "facts" about brain development
have been overturned: Scientists believed that no new synapses or neurons could
grow 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 and
development, it can be helpful in a global way, supporting the cognitive
developmental knowledge; but it cannot provide specific guidance on its own.
With the excitement of the remarkable advances in biology and neuroscience in
recent decades, people naturally want to use brain science to inform policy and
practice, but our limited knowledge of the brain places extreme limits on that
effort. There can be no "brain-based education" or "brain-based parenting" at
this early point in the history of neuroscience!
Thompson: So long as research findings are interpreted carefully, there
are enormous benefits to be gained. As we find out more about how the brain
develops, our medical knowledge is enhanced, and the efficacy of new therapies
can be evaluated in developmental disorders. A second goal is to help
understand how we can optimally learn throughout life: in childhood, and in the
teen years, are there are key times for learning specific skills? Is there a
biological basis to support teaching children certain skills, such as
mathematics, or foreign languages, at specific times? These are exciting
questions. However, surprisingly little is known on these topics. Programs are
emerging to help explore these questions scientifically. A potential danger is
that findings from brain research can be overstretched, or used prematurely, to
support particular learning aids, or commercial products. Parents should
evaluate such claims with caution. Nonetheless, answers are likely to come from
educators, 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 that
promote healthy development or optimal learning. It is of paramount importance
that we are aware, as a society, of the harmful effects on brain development
that result from drug and alcohol abuse in the teenage years, and, in many
countries worldwide, from malnutrition. These are key areas in which
neuroscience research can provide backing, as well as supplementary
information, to help guide policies that address these problems.
Siegel: I have been tremendously excited about the translation of
findings not just in neuroscience, but in a wide range of academic disciplines
studying development, such as anthropology, child psychology, linguistics, and
systems theory, for the non-scientific audience. It has been deeply rewarding
to first become immersed in these scientific fields, explore their similarities
and differences, and then find the convergence of findings despite their
differences in concepts, research methodologies, and vocabulary. The
"consilience" (E.O. Wilson's term from the book of the same name, 1998) of
findings enables an integrated view of the mind, brain, and human relationships
to emerge. I have been amazed at how this interpersonal neurobiology of the
developing mind has been useful to clinicians as well as parents, educators,
clergy, and public policy makers. In recent publications, I have tried to
offer some practical suggestions as to what the translation and integration of
these scientific fields can offer.
There are many ways of exploring the implications for policy or education in
noting the important connections among memory, emotion, relationships.
Experience matters as the mind emerges from how the genetically programmed
maturation of the nervous system responds to ongoing experience. Genes and
experiences shape how neurons become connected to one another. One risk of
over-interpreting the importance of experience can be found in the simplistic and potentially harmful suggestion for early and excessive amounts of sensory
stimulation during infancy. Attachment research suggests that infants
thrive not on excessive stimulation, but rather on forms of collaborative
communication within interpersonal relationships that appear to promote
emotional well-being. This collaborative, contingent form of communication can
be taught to parents. The roots of possible difficulties parents experience
with this form of communication can also be explored to enhance the nurturing
and compassionate connections parents have with their own children. The
integration of a systems view of neuroscience to understanding and promoting
the development of children and adolescents has huge potential benefits for
policy and practice.
Greenough: The results of neuroscience research cannot be translated
into policy by itself. We have many sources of information regarding brain and
behavioral development and learning. The best context for policy development is
a team of individuals that collectively has expertise in child and adolescent
development (especially developmental psychology), education, medicine (e.g.,
child psychiatry) and neuroscience. Working together to interpret the research
and formulate policies that reflect the fullest possible knowledge of the
development process, reasoned and valid policies can be proposed. A volume
that comprises such an interdisciplinary report is "From Neurons to
Neighborhoods: The Science of Early Childhood Development" published by the
National Academy of Sciences. The potential benefits of policies that benefit
or optimize human development are enormous, ranging from the economic effects
of having a vastly more effective workforce to the societal and medical effects
of a population that is as a whole better adapted to the demands of the 21st
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