In our presentation at the 2006 annual meeting of the American Academy of Child and Adolescent Psychiatry, we suggested that child psychiatrists who come across a child with the profile of the following hypothetical case should consider whether the child may have deficits that are not currently covered by DSM-IV nosology: either a nonverbal learning disability (NVLD) or a sensory processing disorder (SPD).
David is an 11-year-old boy with a history of attention-deficit/hyperactivity disorder (ADHD) and a learning disability in mathematics. He has been treated with stimulants and atomoxetine. With medication he has an improved attention span and decreased motor activity, yet both his teachers and his parents note some significant behavioral problems that they attribute to ADHD. David is not oppositional but has a tendency to be inflexible once routines are established and can get into conflicts if changes occur. He will lash out impulsively if someone bumps into him, followed by sincere remorse. He is slow to pick up on social cues but is not distant from others. For example, he interrupts the conversations of others and seems surprised by the negative response from those he interrupts. He prefers larger clothes and fidgets if collars and sleeves are "too tight."
Considering whether a child may have an NVLD or SPD is a "road less traveled" for many behavioral professionals. These disorders may be best thought of as a group of developmentally based higher cortical problems, often in the nondominant hemisphere, that affect a number of functional systems but have no basis in spoken or written language.
Nonverbal learning disabilities
A number of NVLDs have been separately recognized over the years, including disorders of motor control (dyspraxia), visual-spatial processing, mathematics (dyscalculia), music (amusia), memory, executive function, and socioemotional cognition and behavior. Conceptually, these disorders have areas of commonality but are defined primarily by the single symptom of concern. Nevertheless, they all appear to have defects in emotional recognition and expression, social interaction, spatial concepts, prosody (the variation in vocal pitch and rhythm that conveys shades of meaning), and attention.
Because of these common threads, a number of authors have defined a broad-based disorder that involves deficits in executive self-regulation and integrating spatial relationships based in the prefrontal and frontal cortex of the nondominant hemisphere. Therefore, many terms for these disorders may be found in the literature, including NVLD,1,2 right hemisphere deficit,3-5 and developmental socioemotional processing disorder.6
Prefrontal dysfunction results in impairment of executive cortical functions that are used to direct behavior toward a goal and to sustain that behavior over time. Prefrontal dysfunction also inhibits the ability to screen out distractions. While not officially recognized as a learning disability, the Interagency Committee on Learning Disabilities acknowledged the importance of these functions in modifying or amplifying impairments in other cognitive areas. Clinically, the impairment of executive function is increasingly recognized as a disorder that can be diagnosed and treated with intervention strategies.7,8
Frontal lobe executive function
Frontal lobe executive function is divided into 3 specific areas that have general neuroanatomic correlates. The dorsolateral circuit has broad neuroanatomic connections from a large area of the lateral cortex and is the most important for executive function. It subserves cognitive regulation necessary for working memory, organization, planning, problem solving, environmental monitoring, self-awareness, attention, mental flexibility, and abstract reasoning. This circuit specifically controls initiative and initiation, disinhibition, and shifting of cognitive activity.
Behavioral regulation is controlled through the orbitofrontal cortex with deep connections to the basal ganglia complex. Behavioral regulation involves initiation of behavioral responses, inhibition of automatic responses, and delay of immediate gratification (impulse control), sustaining of behavioral and motor response, and anticipation of future consequences.
Finally, the medial cortex through the anterior cingulate circuit with links to the limbic system is responsible for emotional regulation; it modulates emotional arousal, expression of mood, and self-soothing strategies. All of these functions impact internal emotional processes and how they are expressed in a social and environmental context. Behavior may be repetitive and obsessive because of an inability to modify the behavior to fit different social contexts. Conversely, children may be overly dependent on immediate social or environmental cues to guide their behavior and may act based on these cues without reflecting on the appropriateness of their action in a broader social context.
Executive functions show gradual maturation into adolescence, especially attention and response inhibition. NVLDs have greater significance as the child ages and increased function in these systems, particularly the dorsolateral circuit, is expected. Executive processing deficits suggesting NVLD have been found in some children with ADHD as well as in children with conduct disorder and episodic dyscontrol involving both emotion and aggression. These children with NVLD often show a more complex behavioral and cognitive disorder than is expected in children with typical ADHD.
While children with NVLD may be inattentive in most areas, there may be problems in some areas with over- focused or compulsive behavior suggestive of obsessive-compulsive disorder. These children often have problems with transitions and, thus, prioritizing; they are impulsive, moody, and impatient without a clear ability to prioritize or organize. In some situations they are underaroused even as they appear to be restless and talkative. Careful behavioral history and clinical observations of patterns of behavior suggesting an NVLD are often more important for making the initial diagnosis than performing neuropsychological tests, which can determine the full range and degree of executive deficits.9,10
The right hemisphere
The right hemisphere subserves a variety of complex and often interrelated functions. It is dominant for attention and orientation. It is critical for visual-spatial perception and analysis as well as for integrating that information into cognitive processes and learning. Language pragmatics and prosodics are governed by a major right-sided network that is as broadly represented and as complex as the better-known language systems of the dominant hemisphere. Lastly, the right hemisphere is critical for environmental interaction, because it modulates the social and emotional responses to external stimuli. These functions may be affected in isolation, but more often impairment exists in varying combinations that produce complex and, at times, puzzling social, behavioral, and learning profiles.
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