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Research into Learning Disabilities - National Ins
RESEARCH IN LEARNING DISABILITIES AT THE NICHD
CONTRIBUTIONS FROM SCIENTISTS, SUPPORTED BY THE
NATIONAL INSTITUTE OF CHILD HEALTH AND HUMAN DEVELOPMENT
G. Reid Lyon, Ph.D.
Human Learning and Behavior Branch
Center for Research for Mothers and Children
National Institute of Child Health and Human Development
National Institutes of Health
6100 Building, Room 4BO5 9000 Rockville Pike, Bethesda, MD 20892
(301) 496-6591
Fax (301) 402-2085
INTRODUCTION
Learning disabilities (LD) encompass a wide range of
disorders in listening, speaking, reading, writing, and
mathematics that are frequently accompanied by comorbid deficits
in attention and social behavior. Current estimates indicate that
children with LD compose between seven to 10 percent of the
school-aged population and represent over half of the children
who receive special education services in the United States.[1]
Despite this frequency of occurrence, LD remains one of the
least understood yet most disabling conditions that affect both
children and adults. This is unfortunate since learning
disabilities are extremely deleterious to the development
of children in general, and the negative effects of LD go well
beyond school failure. For example, poor peer relationships,
decrements in self-concept, poor post-school adjustment, and
limited placed occupational opportunities are some of the known
outcomes of LD.
A number of influences have contributed to persistent
difficulties in diagnosing and treating LD. In fact, until
research programs supported by the National Institute of Child
Health and Human Development (NICHD) and the Natural Sciences and
Engineering Council of Canada to study learning disabilities
began to lead to major discoveries during the past decade, the
consensus in the biological and behavioral sciences was that the
field of LD lacked scientific validity and clinical utility.[2,3]
To better understand the difficulties that have plagued the LD
field and the NICHD's programmatic response to alleviate them, a
brief review of both problems and progress in the field is
presented in the following sections. Emphasis is placed on
discussing the role of the National Institutes of Health (NIH) in
general, and NICHD in particular, in stimulating and supporting
systematic, prospective longitudinal research to best understand
how to classify, define, and treat LD. As mentioned above,
additional reference will also be made to the outstanding work of
Stanovich and Siegel in LD and reading disorders supported by the
Canadian government.[3] Readers should note that comprehensive
sources on these topics have recently been published.[1,4,5]
IMPEDIMENTS TO SCIENTIFIC DEVELOPMENTS IN LEARNING DISABILITIES:
AN HISTORICAL PERSPECTIVE
Historically, a number of influences have contributed to
difficulties in validating scientifically the construct of
LD.[1,3] First, the field's limitations as a clinical science
can be related to its brief tenure as a recognized category of
disability. Specifically, LD as a federally designated
condition, has been in existence only since 1968.[6] Thus, there
has not been time to collect and consolidate the necessary
observations under experimental conditions that could lead to a
better understanding of the critical diagnostic markers and
treatment interventions that have a known probability of success.
Second, many different theoretical and conceptual views are
offered to explain LD and these views clearly reflect the
multidisciplinary nature of the field.[2] Learning disabilities
are considered the legitimate concern of many disciplines and
professions, including education, psychology, neurology,
neuropsychology, optometry, psychiatry, and speech and language
pathology, to name a few. Each of these professions has focused
on different aspects of the child or adult with LD, so that
there exist highly divergent ideas, and frequently contentious
disagreements about the importance of etiology, diagnostic
methods, intervention methods, and professional roles and
responsibilities. Unfortunately, from the perspective of
developing a valid definition and classification system for
LD, such variation in views and beliefs results in differences in
the numbers of children identified and their characteristics. In
turn, conducting research on samples of children with ostensible
LD who vary widely in diagnostic and demographic characteristics
provides little opportunity for the replication and
generalization of findings - the cornerstones of scientific
inquiry.
Third, many diagnostic and treatment decisions about
individuals with LD have been based on technically inadequate
tests and measures. Recent comprehensive reviews [4] suggest that
fewer than one-third of the psychometric tools used in the
diagnosis of LD meet criteria for adequate norms, reliability,
and validity. As important, the valid assessment of change over
time, and change as a function of treatment, is very difficult to
accomplish at present because few instruments have the scaling
properties to satisfy conditions for the measurement of
individual growth curves.[4]
Fourth and by far the most significant and persistent problem
impeding progress in the field of LD has been the difficulty in
establishing a precise inclusionary definition and a
theoretically based classification system that provides [1] a
framework for the identification of different types of LD, and
[2] a framework for recognizing distinctions and
interrelationships (comorbidities) between LD and other learning
disorders to include attention deficit disorders, general
academic under-achievement, mental retardation. and emotional
disturbance. The precise characterization of LD has been hindered
on the one hand by associating learning disabilities with the
concept of aptitude-achievement discrepancy and on the other hand
by conducting "single-shot" studies on "school-identified" or
"clinic-referred" samples of children.[1,2,3,4] The assumption
that an aptitude (typically assessed using intelligence tests)
achievement discrepancy is a (clear diagnostic marker for LD or
can be considered a pathognomonic sign is at best premature, and
at worst invalid. [2,3,7] Such an assumption is based on the
premise that individuals who display an IQ-achievement
discrepancy are indeed different from individuals who do not with
respect to phenotypic variables such as information processing
characteristics and response to intervention, and genotypic
features such as differences in the heritability of the disorder
or its neurophysiological signature. As will be pointed out
later, a major thrust of the NICHD efforts in the study of LD has
been to evaluate the efficacy of discrepancy in defining learning
disabilities by systematically comparing "discrepant" versus
"non-discrepant" low achieving children on both phenotypic and
genotypic variables [7].
The study of individuals identified a priori as LD by school
or clinic criteria within the context of single investigations or
cross-sectional designs have also significantly hampered efforts
to develop a valid definition and classification system for
learning disabilities. It has been pointed out many times that
schools and clinics lack consistency in the way in which LD is
diagnosed. A child can literally be "cured" of an LD condition
simply by moving across state boundaries or by changing schools
within the same community.[1,2] Such variability in sample
characteristics prohibits replication and generalization of find-
ings - a severe impediment to the development of any clinical
science. Moreover, "single-shot" investigations that compare
children achieving normally with children with LD on
one or more dependent variables of interest at one point in time
ignores the developmental nature of learning and change over
time, and how such change interacts with information
processing characteristics, teacher characteristics, different
interventions, and classroom climates. As such, limited
information is available on the developmental course of LD, and
how children may display different characteristics at different
points in time.
The foregoing brief review provides the rationale for the
development of the NICHD research programs in learning
disabilities. Prior to the initiation of the programs, much of
our research-based thinking about LD was predicated on
information obtained from ambiguously defined school-identified
samples of children who were administered technically inadequate
tests. Frequently the research problem was further confounded by
the tendency to interpret these test data in the context of
invalid theoretical and conceptual frameworks. Finally, the
majority of studies carried out with individuals with LD were not
informed by a longitudinal, developmental perspective. It has
been within this context of scientific need that the NICHD has
systematically developed a portfolio of individual research
initiatives, program projects, and Learning Disability Research
Centers (LDRCS) to define and classify LD, and to obtain new
knowledge related to etiologies, developmental trajectories, and
interventions for learning disabilities. The following sections
provide a review and analysis of the major findings of the
NICHD-supported research projects with an eye toward identifying
additional future research needs and directions.
THE ROLE OF THE NICHD IN THE PLANNING AND CONDUCT OF RESEARCH IN
LEARNING DISABILITIES
By way of background, the Health Research Extension Act of 1985
(P.L. 99-158) mandated the establishment of an Interagency
Committee on Learning Disabilities (ICLD) for the express purpose
of addressing the persistent problems in identifying a valid
classification system and a definition for LD. More specifically,
the ICLD was charged with the task of reviewing and assessing
Federal research priorities, activities, and findings regarding
LD. The NICHD was designated the lead agency for this
congressional initiative. With respect to legislative and
administrative action, the ICLD was required to make
recommendations to increase the effectiveness of research on LD
and to improve the dissemination of findings, and to prioritize
research efforts in the causes, diagnosis, treatment, and
prevention of learning disabilities. Following a comprehensive
review of extant data and information related to the study of
LD,[8] the ICLD concluded that:
"...collaborative, integrated, and coordinated
multidisciplinary approaches to research questions, such as
could be undertaken on university campuses in large program
projects and in specialized research centers of excellence,
would be the most appropriate way to increase the
effectiveness of this research ... A major goal of this
research should be the development of a classification
system that more clearly defines and diagnoses LD, conduct
disorders, and attention deficit disorders, and their
interrelationships. Such information is prerequisite to the
delineation of homogeneous subgroups and the delineation of
more precise and reliable strategies for treatment,
remediation, and prevention that will increase the
effectiveness of both research and therapy. [8]"
Within this context, the NICHD proceeded to develop Requests for
Applications (RFAS) for Program Projects in 1985, Learning
Disability Research Centers (LDRC's) in 1987,[9] and
treatment/intervention research projects in 1993. By way of
background, the Program Project research award is an NIH funding
mechanism that can support at least three discrete, yet closely
related and synergistic projects. The LDRC's are funded via
Specialized Research Center Grants that provide support for both
the synergistic research projects and supporting core service
projects. This type of mechanism is used to stimulate research in
a given field by encouraging collaborative, interdisciplinary
research.
In response to the Program Project RFA, five program
Projects were awarded by the NICHD. The recipients were Dr. John
DeFries and his research group at the University of Colorado, Dr.
Frank Wood and his team at the Bowman Gray School of Medicine,
Dr. Herbert Lubs and his colleagues at the University of Miami,
Dr. Bennett Shaywitz and his collaborators at Yale University and
the University of Houston (led by Dr. Jack Fletcher), and Dr.
Albert Galaburda and his group at Beth Israel Hospital and
Harvard University. In response to the LDRC RFA, three centers
were established; one at Johns Hopkins University under the
leadership of Dr. Martha Denckla, another at Yale University
(also directed by Shaywitz) and one at University of Colorado
(also directed by DeFries). In response to the
treatment/intervention research RFA, one research program was
established at Florida State University under the direction of
Dr. Joseph Torgesen, and one at The University of Houston lead by
Dr. Barbara Foorman. These longitudinal intervention studies are
in the beginning phases and data are not yet available.
A brief overview of the major goals and objectives of the
NICHD Program Projects and LDRC's is provided in the following
sections. Individual Program Projects (Bowman Gray, Miami, Beth
Israel/Harvard) will be summarized first followed by a review of
the research programs that have been awarded an LDRC (Johns
Hopkins) and both a Program Project and an LDRC (Colorado, Yale).
This overview will be followed by sections which provide a
synthesis of the major discoveries made by the research programs
in targeted areas of inquiry (i.e., classification/definition,
reading and language related processes, attention, genetics,
neurophysiology/neuroimaging, and treatment/intervention).
Readers should note that comprehensive reviews of the goals and
findings from each of the projects and centers, written by each
of the principle investigators and their research teams, can be
found in Duane and Gray (1991) [5], Lyon et al.,[1] Fletcher et
al.,[7] and Lyon.[4]
THE NICHD RESEARCH PROGRAMS IN LEARNING DISABILITIES PROGRAM
PROJECTS
The Bowman Gray Program Project is designed to study childhood
reading disability with an eye toward developing a definition and
subtyping system for dyslexia.[5] Within this context, research
studies have been, and continue to be, conducted to [1] identify
an appropriate combination of measures in the first grade that
can define dyslexia and predict reading performance throughout
the later grades, [2] determine whether Attention Deficit
Disorder (ADD) has an independent impact on reading development
and disorders, [3] develop the most powerful combination of
linguistic (e.g., phonological, naming) tasks that can be used to
chart the developmental course of reading and reading disability,
[4] identify the efficacy of code-emphasis reading approaches
versus context-based reading approaches with well-defined groups
of reading disabled children, [5] study regional cerebral blood
flow and positron emission tomographic activation signatures that
are correlated with specific linguistic and cognitive parameters
in a unique sample of adult dyslexics, first seen as children by
Mrs. June Orton, and [6] externally validate distinctions between
dyslexia and ADD using event-related potential electrophysiology.
The University of Miami Program Project has completed its
first five years of investigations to identify inherited subtypes
of specific dyslexia via both behavioral genetic studies and
genetic linkage analyses, and to further characterize these
subtypes by psychophysical, behavioral, and neuroimaging studies.
More specifically, Dr. Lubs and his group have attempted to
define the chromosomal location of the several genes that produce
autosomal dominantly inherited dyslexia. Project goals were
addressed through scientific experiments in three major areas.[4]
In the first area, the Miami group designed and conducted linkage
studies to delineate the location of chromosomes and chromosome
bands of several genes that could be specifically related to a
different phenotypic expressions of dyslexia. In the second area
of investigation, psychophysical and neuropsychological tasks
were administered to dyslexic subjects to delineate information
processing and cognitive profiles that could be used to validate
genetically different subtypes. In the third area, Magnetic
Resonance Imaging and Positron Emission Tomography studies were
carried out in an attempt to identify unique neurophysiological
signatures for dyslexic subtypes.
The Beth Israel/Harvard Program Project has as a primary
goal the development of an understanding of the relationships
between subtle abnormalities of brain development and specific
childhood learning disabilities to include dyslexia. The ultimate
goal of the research is to identify the causes of such neural
anomalies, and thus the neurobiological causes of LD and
dyslexia. [5] Within this context, Dr. Galaburda and his
colleagues have sought to develop an animal model of brain
development that provides a window on how cortical abnormalities
occur during ontogenesis and how such abnormalities affect
behavior. Major efforts have also been deployed to delineate the
cytoarchitectonic organization and the chemoarchitectonics of
those brain regions implicated in developmental dyslexia. In
addition, several investigations are underway to specify
immunological variables responsible for anatomical and behavioral
anomalies in human and animal brain.
The Johns Hopkins LDRC represents a multidisciplinary research
effort designed to understand the neurodevelopmental bases of LD.
Dr. Denckla and her associates pursue this complex research task
through four major lines of research.[4,9] In one project, the
Johns Hopkins group is attempting to discover the causes of
nonverbal LD via behavioral, neuropsychological and neuroimaging
studies of LD individuals and individuals with neurofibromatosis.
A second Project is designed to examine the spectrum and severity
of social deficits in female children who are heterozygous for
the Fragile X genetic anomaly and to investigate the relationship
of these deficits to specific cognitive, linguistic, and
neuropsychological problems observed in LD individuals without
Fragile X. A third line of research is designed to investigate
the relationship between Tourette Syndrome and ADD using both
genetic and neuropsychological procedures. The fourth project is
designed to develop assessment methods to differentiate between
hard to remediate dyslexic children versus children who respond
to intervention. This project is also designed to identify the
most powerful predictors of dyslexia and intervention approaches
that have a high probability of success with disabled readers.
The Colorado Program Project and LDRC. The Colorado Program
Project has been composed of four interrelated projects designed
[1] to assess the genetic etiology of reading disability, and, in
particular, the heritability of phonological and orthographic
skills, [2] to identify the specific language and perceptual
skills that are critical for the development of fluent reading
skills, [3] to determine whether reading disability is correlated
with deficiencies in the immunological system, and [4] to conduct
genetic linkage analyses to localize, if possible, specific genes
implicated in the expression of reading disability. [4,5,9]
With the Colorado LDRC, Dr. DeFries and his group extend the
research carried out in the Program Project by increasing sample
sizes and developing creative behavioral genetic analytic
methodologies to assess the genetic and environmental etiologies
of deficient component phonological, orthographic, reading skills
in reading disability. Within this context, genetic linkage
analysis is being employed to search for major genes and
quantitative trait loci that influence learning disabilities. In
addition, a treatment/intervention project is being conducted
with 100 twin pairs of disabled readers in an effort to dis-
cover reading subtype/dimension by treatment interactions.
The Yale University Program Project and LDRC. The Yale
University Program Project is designed to address major questions
related to the definition, etiology, developmental course, and
biological/neurophysiological bases for dyslexia.[4,5,9] The Yale
studies are unique in that they are being carried out with the
largest longitudinal cohort of reading disabled children in North
America. As such, Dr. Shaywitz and his associates are continuing
to obtain major findings that are not biased by the vagaries of
studying school-identified or clinic-referred samples. In Project
I of the Program Project, the longitudinal cohort is studied to
identify [1] whether distinct subtypes of dyslexia exist, [2]
whether subtypes are stable over time, [3] whether dyslexia
constitutes a developmental lag versus a fixed deficit in
reading, neurolinguistic, and cognitive skills, [4] whether
deficits in single word reading are attributable to a combination
of deficits in phonological and orthographic processes, and [5]
whether positive or negative outcomes of dyslexia are associated
with sociodemographic factors, the nature and severity of the
reading disability, co-morbidity, and self-esteem.
In Project 2, a well defined group of children with early
language disorders is studied to assess the development of
reading-related language skills (e.g., phonological aware-
ness) and to determine how particular early language impairments
relate to the emergence of different types of reading disability.
In Project 3, dyslexic, math disabled, and nondisabled boys and
girls are followed and studied as they pass through puberty in
order to assess the effects of specific endocrinological
influences on reading, cognitive, and neurolinguistic skills.
Finally in Project 4 of the Program Project, the Yale group is
employing state-of-the-art Functional Magnetic Resonance
neuroimaging technology to examine brain structures and brain
functions in well defined groups of dyslexic children as the
children carry out tasks designed to assess reading, phonological
awareness, orthographic decision making, and phonological
decision making skills.
The Yale University LDRC has been charged with the complex
task of developing a comprehensive classification system for the
range of common disorders that can influence school performance.
A major focus of the Center is the development of a
classification system for children with attention and
oppositional/conduct disorders with and without learning disabil-
ities. In addition, one large project within the Center is tasked
with the continued in-depth epidemiological study of 414 reading
disabled children, now entering the ninth grade, who were
originally identified during kindergarten. This ongoing
investigation continues to provide data relevant to the stability
and generalizability of learning disability subtypes over time.
MAJOR FINDINGS AND CONCLUSIONS
A number of independent and replicated discoveries relevant
to learning disabilities in general, and dyslexia in particular,
have been obtained through the research efforts at each of the
NICHD Program Projects and LDRC'S, as well as through the
Stanovich and Siegel research programs funded by the Canadian
government. Selected important discoveries will be highlighted
here according to major domains of study, and those programs
obtaining the findings will be indicated in parentheses. Due to
limitations on the number of references that could be used for
this paper, readers are encouraged to peruse the edited sources
cited for both an overview of the research, an analysis of other
important discoveries, and citations for specific studies.
CLASSIFICATION/DEFINITION
o The definition and classification of learning disabilities
and dyslexia must be accomplished within a longitudinal
developmental framework that does not require adherence to
a priori assumptions reflected in current definitions. Further a
valid definition can best be developed by studies that
investigate representative groups of children over time and that
document how differences among children emerge, change, and
influence further development (Bowman Gray,[5] Yale [1,4,5 7]).
o Current exclusionary definitions of learning disabilities
appear to be invalid, particularly in the area of reading
disabilities and particularly when discrepancy formulae are used
(Yale[7]).
READING AND LANGUAGE RELATED PROCESSES
o Reading disabilities (dyslexia) affect at least 10 million
children, or approximately 1 child in 5 [Yale [9,10]).
o While schools identify approximately four times as many boys
as girls as reading disabled, longitudinal and epidemiological
studies show that as many girls are affected as boys (Bowman
Gray, [5,9] Colorado,[4,9,11] Miami,[5,9] Yale [2,5,7,12]).
o Reading disability reflects a persistent deficit rather than
a developmental lag in linguistic and reading skills.
Longitudinal studies show that of the children who are reading
disabled in the third grade, 74 percent remain disabled in the
ninth grade [Yale,[1,4,7,10] Stanovich & Slegel[3]).
o The practice of distinguishing between disabled readers with
an IQ-Achievement discrepancy and those without a discrepancy
appears invalid.[3,7] More specifically, children with and
without a discrepancy do not differ in the information processing
subskills (phonological and orthographic coding) that are
necessary for the reading of single words.[3] Likewise genetic
and neurophysiological studies have not indicated differential
etiologies for reading disabled children with and without
discrepancies. [1,3,4,7] It remains to be seen whether a
discrepancy between achievement and IQ is a worthwhile predictor
of choice of, or response to, intervention.
o Children with reading disability differ from one another and
from other readers along a continuous distribution, and do not
aggregate together in a distinct "hump" at the tail of the
distribution as once thought (Bowman Gray,[5] Colorado,[4,5]
Yale, [1,4,7,10] Stanovich & Siegel [3]).
o The ability to read and comprehend depends upon rapid and
automatic recognition and decoding of single words and slow and
inaccurate decoding are the best predictors of difficulties in
reading comprehension (Bowman Gray,[5] Colorado, [5,11] Johns
Hopkins,[4] Yale [1,3,5,7].
o The ability to decode single words accurately and fluently
is dependent upon the ability to segment words and syllables into
abstract constituent sound units (phonemes). Deficits in
phonological awareness reflect the core deficit in dyslexia
(Bowman Gray,[5] Colorado,[4,5,11] Johns Hopkins,[4] Miami,[5]
Yale [4,7].
o The best predictor of reading ability/disability from
kindergarten and first grade test performance is phoneme
segmentation ability (Bowman Gray[5,9]) . However there may be
different predictors for different component reading skills. For
example, rapid naming ability may predict word identification
while tasks assessing phonological awareness best predicts
word attack skills (Bowman Gray[5]).
ATTENTION
o A precise classification of ADD with and without
hyperactivity is not yet available. A classification methodology
that assesses internal and external validity of dimensional and
categorical models must be applied to the issue (Yale[1,4]).
o ADD and reading g disability often co-exist, but the two
disorders are distinct and separable (Bowman Gray,[5,9] Yale
[4,5,9].
o ADD occurs more frequently in males and ADD exacerbates the
severity and cognitive morbidity of reading deficits. Since ADD
and reading deficits often co-occur, more males are typically
identified as reading disabled, spuriously inflating the gender
ratio in favor of males (Bowman Gray,[5,9] Miami[9]).
o The effects of ADD on cognitive functioning are variable
with primary deficits in rote verbal learning and memo . ADD
appears relatively unrelated to naming and phonemic awareness
tasks (Bowman Gray[5,9]).
GENETICS
o A multiple regression analytic procedure has been developed
by DeFries and his colleagues that allows for the analysis of the
genetic etiology of individual differences in component language
and reading skills. This is a unique and flexible methodology
that can be used to assess differential genetic and environmental
effects (Colorado [4,5,9,13]).
o There is strong evidence for genetic etiology of reading
disability, with deficits in phonological awareness reflecting
the greatest degree of heritability (Colorado [4,5,13]).
o There appears to be at least one type of reading disability
that can be linked to the HLA region of Chromosome 6 reflecting
an association with autoimmune disorders (Colorado,[5,9] Miami
[9]). Recent evidence obtained from twin and kindred siblings
with severe deficits in reading performance show strong evidence
for a Quantitative Trait Locus on chromosome 6 (Colorado [13]).
NEUROANATOMY, NEUROPHYSIOLOGY, AND NEUROIMAGING
o Several types of brain pathology, including microdysgenesis
(Ectopias), cell loss, and abnormalities of the corpus callosum
are present in a number of strains of immune defective mice.
There is a similarity between the brain lesions seen in the mouse
model and in humans with dyslexia (Beth Israel/Harvard[5,9]).
o At the macroscopic level, atypical neural organization in
dyslexic individuals is suggested by absence of the normal
left-greater-than-right asymmetry in the posterior temporal
planum (Beth Israel/Harvard[5,9]).
o There is converging evidence from anatomical microstructure
studies, gross morphology studies, and neuroimaging studies that
the phenotypic expression in dyslexia is related to anomalous
organization of tissue and processing systems subserved within
the posterior left hemisphere (Beth Israel/Harvard [5,9], Bowman
Gray[5,9]).
o Regional Blood Flow studies indicate that the poor reading
development in dyslexics is associated with less activation than
normal in the left temporal region with atypically increased
activation in the region of the angular gyrus (Bowman Gray[5,9]).
o Positron Emission Tomographic studies indicate that dyslexic
adults have greater than normal activation in regional metabolic
values in the occipital (lingual) and pre-frontal regions of the
cortex (Miami[9]).
TREATMENT/INTERVENTION
o Disabled readers do not readily acquire the alphabetic code
when learning to read due to deficiencies in the processing
of phonological processing. As such, disabled readers must
be presented highly structured, explicit and intensive
instruction in phonics rules and the application of the
rules to print (Bowman Gray [5,9]).
o Longitudinal data indicate that systematic structured
phonics instruction results in more favorable outcomes in
reading than does a context-emphasis (Whole Language)
approach (Bowman Gray [5,9].
o Dyslexic readers who have been remediated and who are at
normal to near normal reading levels in adulthood continue
to display atypical neural processing as assessed by
regional cerebral blood flow studies. This finding suggests
that initial neuropathology remains stable over time,
despite remediation, and that compensatory mechanisms may be
developed (Bowman Gray [5,9]).
FUTURE RESEARCH DIRECTIONS IN LD
In addition to the research initiatives and programs described
above, the NICHD is developing and expanding programs and plans
in area of treatment/intervention for LD children and in the area
of cognitive neuroscience and neuroimaging. Each of these areas
of inquiry are described briefly.
TREATMENT/INTERVENTION
Review of the literature related to reading disabilities and
other learning disabilities indicates that no single
treatment/intervention approach or method is likely to yield
clinically significant, long-term, therapeutic gains with
children diagnosed with LD.[1,2] Unfortunately, to date, there
exists scant scientific support for the use of particular inter-
ventions or combinations of interventions with different types of
learning disabilities. Because of this, the NICHD has recently
launched a major research effort to determine which treatment
methods or combinations of methods, provided in which setting,
have the most effective impact on well defined domains of child
functioning, for how long, and for what reasons. Within this
context, two highly controlled and well designed Longitudinal
prospective intervention studies with LD children are now being
supported at the Florida State University under the direction of
Dr. Joseph Torgesen and the University of Houston under the
direction of Dr. Barbara Foorman. Additional
treatment/intervention initiatives are being planned at this
time.
COGNITIVE NEUROSCIENCE AND NEUROIMAGING
There exists a critical need to understand how the human brain is
organized for complex behaviors, and to know more specifically
how the child with LD and the normal learner differ with respect
to central nervous system functioning. In addition, it is impor-
tant for us to understand how such physiological and
neuroanatomical differences are related to indices of
heritability and environmental influences. Our ability to assess
brain-behavior relationships in an accurate, yet noninvasive
manner, is improving significantly as we begin to employ dramatic
new advances in neuroimaging technology. For instance,
The Shaywitz group at Yale is moving forward with the application
of Functional Magnetic Resonance Imaging studies with reading
disabled and nor al children. In addition, Dr. Allen Reiss and
his colleagues at Johns Hopkins are designing imaging software
that will allow different sites to compare neuroimaging data and
how best to register functional brain information with structural
brain information. These projects, as well as initiatives
being planned, should serve to provide the empirical foundation
necessary to not only understand the limits of individual
variability in brain structure and function, but to identify the
neurobiological underpinnings of learning disabilities.
SUMMARY
The NICHD has been, and will continue to be responsive to the
critical research needs in LD and related disorders. As an index
of the heightened research activity in this arena, consider that
NICHD support for projects related to learning and language dis-
abilities has increased from $1.75 million in 1975 to over $15
million in 1993-a cumulative total of approximately $80 million.
Given the significant discoveries made by the Program Projects,
LDRC's and individual research grants supported through these
increases, the money clearly has been well spent. Within the past
10 years, NICHD research has identified the major cognitive
mechanisms underlying dyslexia and other learning disabilities
and how the assessment of these mechanisms can help to predict
the onset, developmental course, and outcomes of such disorders.
Moreover, NICHD scientists have contributed substantially to an
understanding of how the genome, the brain, and the environment
interact to produce individual variations in learning. Given this
knowledge, we are hopeful that the newly funded
treatment/intervention projects will provide guidance with
respect to ameliorating the devastating effects of learning
disabilities on both children and adults.
REFERENCES
1 .Lyon GR, Gray DB, Kavanagh, JF, et al (Eds): Better
Understanding Learning Disabilities: New Views from Research and
Their Implications for Education and Public Policies.
Baltimore, Brookes, 1993.
2. Moats, LC, Lyon GR: Learning disabilities in the United
States: Advocacy science, and the future of the field. J Learn
Disab 1993; 26:282-294.
3. Stanovich KE, Siegel LS: Phenotypic performance profile of
children with reading disabilities: A regression-based test of
the phonological-core variable-difference model. J Ed Psych
1994; 86:24-53.
4. Lyon GR (Ed): Frames of Reference for the Assessment of
Learning, Disabilities: New Views on Measurement Issues.
Baltimore, Brookes, 1994.
5. Duane DD, Gray DB (Eds): The Reading Brain: The Biological
Basis of Dyslexia. Parkton, MD: York, 1991.
6. National Advisory Committee on Handicapped Children: Special
Education for Handicapped Children. Washington, D.C., Department
of Health, Education, and Welfare, 1968.
7. Fletcher JM, Shaywitz SE, Shankweller DP, et al: Cognitive
profiles of reading disability: Comparisons of discrepancy and
low achievement definitions. J Ed Psych 1994; 86:6-23.
8. Kavanagh JF, Truss TJ (Eds): Learning Disabilities:
Proceedings of the National Conference. Parkton, MD: York, 1988.
9. Lyon GR: Research in Learning Disabilities (Tech. Rep.).
Bethesda MD: National Institute of Child Health and Human
Development, 1991.
10. Shaywitz SE, Escobar MD, Shaywitz, BA et al.: Evidence that
dyslexia may represent the lower tail of a normal distribution of
reading disability. N Engl J Med 1992; 326:145-150.
11. Olson R, Forsberg H, Wise B et al.: Measurement of word
recognition, orthographic, and phonological skills, in Lyon GR
(Ed): Frames of Reference for the Assessment of Learning
Disabilities: New Views on Measurement Issues. Baltimore,
Brookes, 1994, pp 243-278.
12. Shavwitz SE, Shaywitz, BA, Fletcher, JM et al.: Prevalence of
reading disability in boys and girls: Results of the Connecticut
longitudinal study. JAMA 1990; 264:998-1002.
13. Cardon LR, DeFries JC, Fulker DW et al.: Quantitative trait
locus on chromosome 6 predisposing to reading disability. Science
(in press).
14. Gray DB, Kavanagh JF (Eds): Biobehavioral Measures of
Dyslexia. Parkton, MD: York.
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