Neurodevelopmental and Executive Function and Dysfunction

Sensory and Motor Function

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. Sensory development progresses in association with environmental exposure and with the development of other cognitive processes, such as motor development. Through sensory experiences, children's brains mature as new neuronal pathways are created and existing pathways are strengthened.

There are three distinct, yet related, forms of neuromotor ability: fine motor, graphomotor, and gross motor coordination. Fine motor function reflects the ability to control the muscles and bones to produce small, exact movements. Deficits in fine motor function can disrupt the ability to communicate in written form, to excel in artistic and crafts activities, and can interfere with learning a musical instrument or mastering a computer keyboard. 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 can significantly impede writing. Children who harbor weaknesses of visualization during writing have trouble picturing the configurations of letters and words as they write (orthographics), with poorly legible written output with inconsistent spacing between words. Others have weaknesses in orthographic memory and may labor over individual letters and prefer printing (manuscript) to cursive writing. Some exhibit signs of finger agnosia and have trouble localizing their fingers while they write, needing to keep their eyes very close to the page and applying excessive pressure to the pencil. Others struggle producing the highly coordinated motor sequences needed for writing, a phenomenon also 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).

Gross motor function refers to control of large muscles. Children with gross motor incoordination often have problems in processing “outer spatial” information to guide gross motor actions. Affected children may be 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 evidence difficulties 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 may be difficult for them to recall or plan complex motor procedures such as those needed for dancing, gymnastics, or swimming.

Language

Language is one of the most critical and complex cognitive functions and can be broadly divided into receptive (auditory comprehension/understanding) and e xpressive (speech and language production and/or communication) functions. Children who primarily experience 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 production and/or problems with higher-level language development. Speech production difficulties include oromotor problems affecting articulation, verbal fluency, and naming. Some children have trouble with sound sequencing within words. Others find it difficult 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 result in difficulty finding exact words when needed (as in a class discussion) or substituting definitions for words (circumlocution).

The basic components of language include phonology (ability to process and integrate the individual sounds in words), semantics (understanding the meaning of words), syntax (mastery of word order and grammatical rules), discourse (processing and producing paragraphs and passages), metalinguistics (ability to think about and analyze how language works and draw inferences), and pragmatics (social understanding and application of language). Children who evidence higher-level expressive language impediments have trouble formulating sentences, using grammar acceptably, and organizing spoken (and possibly written) narratives.

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 often experience problems with academic performance. In fact, some studies suggest that up to 80% of children who present with a specific learning disorder also experience language-based weaknesses. Additionally, the role of language in executive functioning cannot be understated, since language serves to guide cognition and behavior.

Visual-Spatial/Visual-Perceptual Function

Important structures involved in the development and function of the visual system include the retina, optic cells (e.g., rods and cones), the optic chiasm, the optic nerves, the brainstem (control of automatic responses, e.g., 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 located in space (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 left hemisphere processing of details, patterns, and linear information and right hemisphere processing of the gestalt and overall form.

Critical aspects of visual processing development in the child include appreciation of spatial relations (ability to perceive objects accurately in space in relation to other objects), visual discrimination (ability to differentiate and identify objects based on their individual attributes, e.g., size, shape, color, form, position), and visual closure (ability to recognize or identify an object even when the entire object cannot be seen). Visual-spatial processing dysfunctions are rarely the cause of reading disorders, but some investigations have established that deficits in orthographic coding (visual-spatial analysis of character-based systems) can contribute to reading disorders. Spelling and writing can emerge as a weakness because children with visual processing problems usually 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 difficulty managing geometric material. In the social realm, intact visual processing allows a child to make use of visual or physical cues when communicating and interpreting the paralinguistic aspects of language. Secure visual functions are also necessary to process proprioceptive and kinesthetic feedback and to coordinate movements during physical activities.

Intellectual Function

A useful definition of intellectual function is the capacity to think in the abstract, reason, problem-solve, and comprehend. The concept of intelligence has had many definitions and theoretical models, including Spearman's unitary concept of “the g-factor,” the “verbal and nonverbal” theories (e.g., Binet, Thorndike), the 2-factor theory from Catell (crystallized vs fluid intelligence), Luria's simultaneous and successive processing model, and more recent models that view intelligence as a global construct composed of more-specific cognitive functions (e.g., auditory and visual-perceptual processing, spatial abilities, processing speed, working memory).

The expression of intellect is mediated by many factors, including language development, sensorimotor abilities, genetics, heredity, environment, and neurodevelopmental function. When an individual's measured intelligence is >2 standard deviations below the mean (a standard score of <70 on most IQ tests) and accompanied by significant weaknesses in adaptive skills, the diagnosis of intellectual disability may be warranted (see Chapter 53 ).

Functionally, some common characteristics distinguish children with deficient intellectual functioning from those with average or above-average abilities. Typically, those at the lowest end of the spectrum (e.g., profound or severe intellectual deficiencies) are incapable of independent function and require a highly structured environment with constant aid and supervision. At the other end of the spectrum are those with unusually well-developed intellect (“gifted”). Although this level of intellectual functioning offers many opportunities, it can also be associated with functional challenges related to socialization and learning and communication style. Individuals whose intellect falls in the below-average range (sometimes referred to as the “borderline” or “slow learner” range) tend to experience greater difficulty processing and managing information that is abstract, making connections between concepts and ideas, and generalizing information (e.g., may be able to comprehend a concept in one setting but are unable to carry it over and apply it in different situation). In general, these individuals tend to do better when information is presented in more concrete and explicit terms, and when working with rote information (e.g., memorizing specific material). Stronger intellect has been associated with better-developed concept formation, critical thinking, problem solving, understanding and formulation of rules, brainstorming and creativity, and metacognition (ability to “think about thinking”).

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, fornix, temporal lobes, and 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 (typically seconds) during which this information is being held and/or manipulated for registration, and ultimately encoded, consolidated, and retained, is referred to as working memory . Other descriptors include short-term memory and immediate memory . Consolidation and storage represent the process by which information in short-term memory is transferred into long-term memory . Information in long-term memory can be available for hours or as long as a life span. Long-term memories are generally thought to be housed, in whole or in part, in specific brain regions (e.g., cortex, cerebellum). Ordinarily, consolidation in long-term memory is accomplished in 1 or more of 4 ways: pairing 2 bits of information (e.g., a group of letters and the English sound it represents); storing procedures (consolidating new skills, e.g., 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 long-term memory, 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 (capacity to learn from a single point in time forward), retrograde memory (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 . Automatization reflects the ability to instantaneously access what has been learned in the past with no expenditure of effort. Successful students are able to automatically form letters, master mathematical facts, and decode words.