Neurodevelopmental Function and Dysfunction in the School-Aged Child

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Chapter 29 Neurodevelopmental Function and Dysfunction in the School-Aged Child

A neurodevelopmental function is a basic brain process needed for learning and productivity. Neurodevelopmental variation refers to differences in neurodevelopmental functioning. Wide variations in these functions exist within and between individuals. These differences can change over time and need not represent pathology or abnormality. Neurodevelopmental dysfunctions reflect disruptions of neuroanatomic structure or psychophysiologic function that may be associated with problems related to cognition, academics, and/or behavioral, emotional, social, and adaptive functioning.

Terminology and Epidemiology

The primary manifestation of neurodevelopmental dysfunction is academic disability. Academic disorders have been diagnostically classified by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) and the International Classification of Diseases (ICD) of the World Health Organization. The DSM-IV-TR separates academic disorders into reading disorder, mathematics disorder, and disorder of written expression, and it differentiates these disorders from motor skills disorders and communication disorders. Other diagnostic terms such as dyslexia (reading), dyscalculia (mathematics), or dysgraphia (written expression) are used primarily in neurologic classifications.

Traditionally, the educational system has identified specific learning disabilities (SLD) through the process of psychoeducational testing. Through this process, students experiencing academic problems would be evaluated psychometrically. Typical testing batteries have usually included measures of overall intelligence, academic skills, and adaptive functioning. A student exhibiting a significant discrepancy between scores on tests of intelligence (aptitude) and tests of academic achievement could be classified as a student with an SLD and would subsequently be eligible for special education services (e.g., resource support). The degree of discrepancy required for such classification differs between states and even between school districts. The reauthorization in 2004 of the Individuals with Disabilities Education Act (IDEA) incorporated the Response to Intervention (RTI) model, which does not necessitate that education agencies use the discrepancy model for determining if a student has an SLD. Instead, schools may employ research-based intervention approaches and monitor a student’s response to that intervention before initiating psychoeducational testing. This major shift in educational policy will likely lead to future changes in epidemiologic rates.

Overall estimates of the prevalence of academic disabilities range from 3-10%, with more recent data indicating that approximately 8% of children 3-17 yr of age have, at one point, been identified as having an academic disability. The prevalence rate for disorders of attention (e.g., ADHD; Chapter 30) in this same age span is reported at 7.4%, with boys identified at a significantly higher rate than girls (9.5% and 5.9%, respectively). Prevalence estimates can vary owing to numerous factors, including differences in definitions and criteria used for classification and diagnosis and differences in methods of assessment.

Etiology

Multiple factors underlie neurodevelopmental dysfunctions. These include genetic, medical, psychologic, environmental, and sociocultural influences. Some of the genes that contribute to neurodevelopmental dysfunction have been identified. It is well established that reading disorders can be both familial and heritable; studies have linked some reading disabilities to specific gene loci on chromosomes 6 and 15. Chromosomal abnormalities can lead to unique patterns of dysfunction, such as visual-spatial deficits in girls with Turner’s syndrome or language deficits in persons with fragile X syndrome (Chapter 76). Gene-deletion syndromes such as velocardiofacial syndrome are associated with predictable patterns of neurodevelopmental dysfunction (attention and working memory deficits, with academic difficulties in reading comprehension and mathematics conceptualization).

Perinatal risk factors that have been associated with neurodevelopmental dysfunction include very low birth weight, severe intrauterine growth restriction, perinatal hypoxic-ischemia encephalopathy, and prenatal exposure to alcohol and other drugs (Chapter 90). Increased risk of academic and attention disorders is associated with environmental toxins, including lead (Chapter 702); drugs such as cocaine; infections, such as meningitis and HIV; and brain injury secondary to intraventricular hemorrhage or head trauma. There have been conflicting reports regarding the contribution of persistent otitis media with effusion and associated conductive hearing loss to subsequent language problems.

Psychological influences can also result in and/or exacerbate neurodevelopmental dysfunctions. Some research has postulated that early psychological trauma can result in both structural and neurochemical changes in the developing brain, which may contribute to neurodevelopmental dysfunction. Some findings suggest that the effects of exposure to trauma and/or abuse early in the developmental course can induce disruption of a brain regulatory system with connections in the orbitofrontal cortex and can influence right-hemisphere function with associated risk for problems with information processing, memory, development of academic skills, and overall functioning (e.g., attention and self-regulation). Environmental and sociocultural deprivation can lead to, or potentiate, neurodevelopmental dysfunction. In the child with an academic skills disorder (e.g., reading, written expression, or mathematics), often there are a combination of etiologic factors contributing, and a single cause is seldom ascertained.

Core Neurodevelopmental Functions

The neurodevelopmental processes that are critical for academic success fall within core neurodevelopmental domains.

Sensory and Motor Development

Sensory development (e.g., auditory, visual, tactile, proprioceptive) begins well before birth. This neurodevelopmental process is crucial in helping children experience, understand, and manipulate their environments and is a vital mechanism for basic survival. Through sensory experiences, children’s brains mature as new neuronal pathways are created and existing pathways are strengthened. Sensory development for the school-age child progresses in association with motor development, with the two processes having a symbiotic relationship. Motor movements can be separated into three categories: continuous, discrete, and procedural movements. Of these, procedural movements represent motor functions that are most relevant to daily life (e.g., manipulating utensils).

Motor development can also be broken down into three distinct, yet related, forms of neuromotor ability: fine motor, graphomotor, and gross motor coordination. In school, problems with fine motor function can affect a child’s ability to excel in artistic and crafts activities and can interfere with learning a musical instrument or mastering a computer keyboard. Eye-hand incoordination may be prominent because the child has trouble with the rapid and precise integration of visual inputs with specific motor plans. Some children have difficulty remembering fine motor sequences, such as those required for tying shoelaces. The term dyspraxia relates to difficulty in developing an ideomotor plan and activating coordinated and integrated visual-motor actions to complete a task or solve a motor problem, such as assembling a model.

Graphomotor function refers to the specific motor aspects of written output. Several subtypes of graphomotor dysfunction significantly impede writing. Some students harbor weaknesses of visualization during writing. They have trouble picturing the configurations of letters and words as they write (orthographics). Their written output tends to be poorly legible, with inconsistent spacing between words. Others have weaknesses in graphomotor memory, the ability to recall letter and number forms rapidly and accurately. They labor over individual letters and prefer printing (manuscript) to cursive writing. Some exhibit signs of finger agnosia or weak graphomotor feedback; they have trouble localizing their fingers while they write. As a result, they need to keep their eyes very close to the page and tend to apply excessive pressure to the pencil. Others struggle with graphomotor production deficits. Such students have trouble producing the highly coordinated motor sequences needed for writing and have difficulty assigning writing roles to specific muscle groups in their hands. This phenomenon has also been described as dyspraxic dysgraphia. It is important to emphasize that a child may show excellent fine motor dexterity (as revealed in mechanical or artistic domains) but very poor graphomotor fluency (with labored or poorly legible writing).

Some children exhibit gross motor incoordination. They have problems in processing “outer spatial” information to guide gross motor actions. Affected children are inept at catching or throwing a ball because they cannot form accurate judgments about trajectories in space. Others demonstrate diminished body position sense. They do not efficiently receive or interpret proprioceptive and kinesthetic feedback from peripheral joints and muscles. They are likely to be impaired when activities demand balance and ongoing tracking of body movement. Others are unable to satisfy the motor praxis demands of certain gross motor activities. It is hard for them to recall or plan complex motor procedures (such as those needed for dancing, gymnastics, or swimming). Children with gross motor problems can incur considerable embarrassment in physical education classes. Gross motor weaknesses can lead to social rejection, withdrawal, and generalized feelings of inadequacy.

Language

Language may be the most critical cognitive function humans develop. Brain imaging confirms areas of brain specialization for language development (e.g., for processing of phonological, orthographic, semantic, and syntactic information), along with increased connections and integration between language association areas, dominance of the left hemisphere in language processing, and the presence of “language control” regions. Language dysfunction has been linked to reduced cerebral volume and underactivation in the perisylvian areas, planum temporale, temporal lobes, and frontal lobes.

Disordered language occurs in many forms. Some children have particular problems with phonology (Chapter 32). They experience unclear reception of language sounds and have difficulty discriminating between, and forming associations with, the sounds of their native language. For the brain to process these language sounds, it must, for example, accommodate the very rapid transition (∼30 msec in duration) from the sound k to the uh in kuh. In some cases, affected students have trouble processing these acoustic signals within language sounds rapidly enough. Commonly, a weak phonologic sense has a negative effect on reading, as well as other academic skills. A student with a poor appreciation of language sounds is likely to form unstable associative linkages between those sounds and visual symbols (letter combinations). It can be hard for these students to conceptualize words as made up of language sound segments (phonemes); thus, their ability to break words down into their constituent sounds and then reblend them into pronounceable words is impeded. They can also have problems manipulating language sounds in their minds and blending them to form a word.

Children with semantic deficits have trouble learning the meaning of new words and using words appropriately. Other common language deficiencies include difficulty with syntax (word order), problems with discourse (paragraphs and passages), an underdeveloped sense of metalinguistics (how language works), and trouble with drawing appropriate inferences (supplying missing information) from language. Difficulty with pragmatic language skills, or the social applications of language, can be another significant impediment.

It is important to distinguish between receptive language dysfunctions (problems with auditory comprehension/understanding) and expressive language dysfunctions (problems with speech and language production and/or communication). Children with primarily receptive language problems may have difficulty understanding verbal information, following instructions and explanations, and interpreting what they hear. Expressive language weaknesses can result from problems with speech as well as language. Speech difficulties include oromotor problems affecting articulation, verbal fluency, and naming. Some students have trouble with sound sequencing within words. Others find it hard to regulate the rhythm or prosody of their verbal output. Their speech may be dysfluent, hesitant, and inappropriate in tone. Problems with word retrieval can also thwart expressive language fluency. Despite an adequate vocabulary, affected children have problems in finding exact words when they need them (as in a class discussion). They may show marked hesitation and keep substituting definitions for words (circumlocution). Children with expressive impediments have trouble formulating sentences, using grammar acceptably, and organizing spoken (and possibly written) narratives.

Language weaknesses can also manifest in content areas such as the sciences, which necessitate the processing of dense verbal material in textbooks and the rapid convergent recall of facts, and social studies courses that often entail the use of sophisticated language and verbal abstract concepts (e.g., democracy). Learning foreign languages can be a serious problem. In particular, those with even mild trouble with phonologic awareness, semantics, or syntax in their primary language can have serious problems adding a second language. In contrast, students who possess strong language abilities can make use of their linguistic facility to compensate for any academic problems; it may be possible to verbalize one’s way through a mathematics curriculum, thereby circumventing a tendency to be confused by predominantly nonverbal concepts (ratio, equation, diameter).

Some studies have linked expressive language dysfunction to delinquent behavior. This may be especially true when an expressive language disorder occurs in a context of environmental deprivation or turmoil. To one degree or another, all academic skills are taught largely through language, and thus it is not surprising that children who experience language dysfunction usually have troubled educational careers. Up to 80% of children with academic disabilities have problems that are language-based.

Visual-Spatial and Perceptual Functioning

Vision begins well before birth, with continued development and refinement throughout childhood (Chapter 613). Important structures involved in the development and function of the visual system, beyond the eyes themselves, include the retina, optic cells (e.g., rods and cones), the optic chiasm, the optic nerves, the brainstem (control of automatic responses like pupil dilation), the thalamus (e.g., lateral geniculate nucleus for form, motion, color), and the primary (visual space and orientation) and secondary (color perception) visual processing regions located in and around the occipital lobe. Other brain areas, considered to be outside of the primary visual system, are also important to visual function, helping to process what (temporal lobe) is seen and where it is (parietal lobe). It is now well documented that the left and right cerebral hemispheres interact considerably in visual processes, with each hemisphere possessing more specialized functions including processing of details, patterns, and linear information mediated by the left hemisphere and processing of the gestalt, form, and integrative functions mediated by the right hemisphere.

The function of vision has many components, ranging from basic sensory identification to visual acuity, identification of form, color, and location, perceptual impairments (e.g., depth perception), perception of relative size, foreground and background relationships, and form constancy, to integration of visual information with other functions, such as motor output and development of language and academic skills (e.g., reading, writing, and mathematics). Children with obvious visual impairments are easily identified; many children with more subtle or milder deficits (and even some with more pronounced impairments) are often misidentified and/or missed completely. Indications of visual processing deficits in the school-aged child may be difficulty learning to draw and write and problems with crafts activities. These children often have trouble discriminating between left and right. They might encounter problems recognizing letters and words, resulting in delayed reading, spelling, and writing.

Although many authors have argued that visual-spatial processing dysfunctions are not, in themselves, a common cause of chronic reading disorders, more recent investigations have established that deficits in both orthographic coding (visual-spatial analysis of character-based systems) and phonological processing can contribute to reading disorders. Spelling and writing can emerge as a weakness because children with visual processing problems commonly have trouble with the precise visual configurations of words. In mathematics, these children often have difficulty with visual-spatial orientation, with resultant difficulty aligning digits in columns when performing calculations and/or difficulty managing geometric material. In the social realm, intact visual processing allows a child to make use of nonverbal or physical cues when communicating and interpreting paralinguistics. These functions are also necessary to process proprioceptive and kinesthetic feedback and to coordinate movements during physical activities. Children with visual processing deficits are thus susceptible to problems such as social isolation and withdrawal and consequent behavioral and/or emotional difficulties.

Memory

Memory is a term used to describe the cognitive mechanism by which information is acquired, retained, and recalled. Structurally, some major brain areas involved in memory processing include the hippocampus, the fornix, the temporal lobes, and the cerebellum, with connections in and between most brain regions. The memory system can be partitioned into subsystems based on processing sequences; the form, time span, and method of recall; whether memories are conscious or unconsciously recalled; and the types of memory impairments that can occur.

Once information has been identified (through auditory, visual, tactile, and/or other sensory processes), it needs to be encoded and registered, a mental process that constructs a representation of the information into the memory system. The period of time (typically seconds) during which this information is being held and/or manipulated for registration, and ultimately encoded, consolidated, and retained, is sometimes referred to as working memory (WM). Other descriptors include short-term memory (STM) and immediate memory (IM). Consolidation and storage represent the process by which information in STM is transferred into long-term memory (LTM). Information in LTM can be available for hours or as long as a lifespan. LTMs are generally thought to be housed, in whole or in part, in various brain regions (e.g., the cortex, cerebellum). Ordinarily, consolidation in LTM is accomplished in one or more of four ways: pairing two bits of information (such as a group of letters and the English sound it represents); storing procedures (consolidating new skills, such as the steps in solving mathematics problems); classifying data in categories (filing all insects together in memory); and linking new information to established rules, patterns, or systems of organization (rule-based learning).

Once information finds its way into LTM, it must be accessed. In general, information can be retrieved spontaneously (a process known as free recall) or with the aid of cues (cued or recognition recall). Some other common descriptors of memory include anterograde memory (the capacity to learn from a single point in time forward), retrograde memory (the capacity to recall information that was already learned), and explicit memory (conscious awareness of recall), implicit memory (subconscious recall: no awareness that the memory system is being activated), procedural memory (memory for how to do things), and prospective memory or remembering to remember.

As children proceed through school, the demands for the efficient use of memory progressively increase. By secondary school, rapid and precise recall is heavily emphasized. Children can have trouble with one or more memory mechanism. They might struggle with the initial registration of information in STM. Others might have difficulty storing newly introduced information. Other children might have difficulty accessing (retrieving) information, despite having registered and stored it effectively. Children can experience frustration in their efforts at consolidating information into LTM and/or encounter difficulty with simultaneous recall (retrieval of several facts or procedures at once). Some students exhibit delayed automatization: Not enough of what they have learned in the past is accessible to them instantaneously and with no expenditure of effort. Such skills as forming letters, mastering mathematical facts, and decoding words must ultimately become automatic if students are to make good academic progress.

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