I am frequently asked - "Does this child have an attention deficit disorder, or is it a sensory integration disorder?" I generally respond that I don't know what either ADHD or sensory integration disorders are.
There is a fundamental problem that we have in diagnostic evaluation: professions have created 'disorders' before there is an understanding of the mechanisms underlying the disorders. This opens up the possibility for criticism because we begin calling 'disorders' by names and then have no basis for backing up our opinions. I still feel relatively comfortable stating that I don't know what ADHD or sensory integration dysfunctions are. This confuses people who are looking for answers but I believe it to be the most honest response that is possible for this question.
I believe that there are multifactorial reasons why children behave the way they do. Some of those reasons are neurologically based and some are behaviorally based. I wanted to focus on the neurobiology of arousal and attention mechanisms as a starting point.
A discussion on the topics of arousal and attention first requires an operational definition of the terms. William James wrote that "Everyone knows what attention is. It is the taking possession by the mind in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought...It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrained state." (James, 1890, p. 403). Current theorists are now challenging this perspective on attention and are identifying models of attention that focus on parallel processing or multitasking abilities (Pashler, 1998).
The construct of attention is dependent on the construct of arousal. Arousal is often equated with consciousness, which has also been defined in many different ways. Primary and secondary consciousness, from Edelman and Tononi’s perspective (2000), does not seem to have a single point of residence in the nervous system, but instead is regulated by the interaction of several centers. However, from a more specific and limited definition that has clinical utility, some specific structures can be considered that contribute to arousal level.
Review of the neurological structures governing arousal/attention and their interrelationships.
The reticular activating system is the center for all arousal except for smell (Dodd & Castellucci, 1991, p. 517). Bilateral destruction of the ascending reticular formation projections to the midline and intralaminar nuclei of the thalamus is known to cause coma (Kelly, 1991, pp. 815-816).
The hypothalamus is also important for regulating autonomic responses to arousing stimuli. There are specific and measurable behaviors associated with arousal and orientation toward novel stimuli. These include pupillary dilation, vasoconstriction of the limbs, vasodilation of the head, increased electrodermal activity, and cardiorespiratory regulation (DeGangi & Porges, 1990, pp. 7-8).
The limbic system is also important in the arousal/attention process by coordinating autonomic, somatic, and behavioral systems (p. 15). People who have limbic system damage may have difficulties with qualitative analysis of incoming stimuli causing inattention, overattention, or inability to functionally interpret the meaning or importance of the stimuli.
The reticular activating system, hypothalamus, and limbic systems and their associated functions are closely coordinated in a pattern of inhibition and feedback loops between the cortex and the lower structures (p. 13). A functional overview of the mechanism associated with arousal/attention includes receiving the initial stimulation, regulation of arousal and sensory registration, activation of the alerting and orienting responses, and then selective attention or inattention. All of these functions occur under cortical direction, both directly and indirectly.
Hypothesized location of the neurological disorder
The neurological basis of ADHD has been debated for the last several decades. Some researchers hypothesize that the frontal lobes of patients with ADHD may be involved, as this is the site of cortical control over lower brain arousal and orienting functions (Blum & Mercugliano, 1997, p.451). It is thought that catecholamine neurotransmitters such as dopamine and norepinepherine are deficient because stimulant medications that are prescribed for the disorder are known to increase the availability of these neurotransmitters (p. 451). Other studies indicate that size of selected brain structures may be decreased in some children who have ADHD (p. 451). Some researchers have identified that subcortical structures are implicated in the ADHD disorder (Kinomura, Larssen, Gulyas, & Roland, 1996). Some professionals suggest that ADHD is more of a behavioral style than a diagnostic entity with a specified or identifiable location of neurological deficit (Chess & Thomas, 1987). Still other physicians openly question the validity of the diagnosis ADHD, suggesting that there is no such disorder at all (Victoroff, 2000).
Specific symptoms of dysfunction
According to the DSM-IV (APA, 1994) diagnostic criteria for attention deficit hyperactivity disorder include both symptoms of inattention and symptoms of hyperactivity or impulsivity. These symptoms must be present for at least six months and of a degree that is maladaptive and inconsistent with developmental level. Additionally, these symptoms must appear prior to the age of seven, must be present in more than one setting, and not due to any other confounding disorder.
Despite these clear criteria for diagnosing ADHD, many children are not identified with this disorder until they are school-aged. Prior to this time they may be identified as having a regulatory disorder, as described by DeGangi (2000).
Difficulties with maintaining sustained attention are especially problematic when the child enters elementary school. During these early school years the child may have difficulties with complying with classroom rules and routines (Blum & Mercugliano, 1997, p. 450). As children get older, social concerns are more prevalent. In the majority of people who have ADHD, symptoms persist into adolescence and adulthood (p. 450). This causes long term and chronic occupational dysfunction. Children who have attention deficit hyperactivity disorder are more likely to have co-morbid conduct and mood disorders (p. 450).
Etiology of ADHD
Some researchers now believe that ADHD may be a genetic disorder (Todd, 2000). ADHD as defined by DSM-IV criteria includes a clinical spectrum of disorders that may have multiple etiologies. Common to these disorders is the symptom of inattention.
Evidence suggests that attention is a neuropsychological function and that disorders of attention are biologically based. Epidemiological data, the measured effectiveness of selected pharmacological intervention, and neuroimaging all continue to contribute to the current understanding of this disorder. Despite a substantial amount of research and popular attention in the media there is still no commonly agreed on cause of the disorder or universally accepted intervention protocols.
Implications for Occupational Performance
Regulation of attention and arousal is a basic requirement for human function. DeGangi and Porges state that "when a person is actively engaged in voluntary attention, functional purposeful activity and learning can occur" (p. 6). Attention deficit disorder is the most common neurodevelopmental disorder of childhood, with an estimated prevalence of 3%-5% among school-age children and a male to female ratio of 4:1 -9:1 (Blum & Mercugliano, 1997, p. 449).
The disorder has a significant impact on the academic participation of many children. A basic model for understanding the relationship between arousal and performance is described by Lane (2001, p. 133). In this model, performance is most notably decreased in periods of excessively high or excessively low arousal; peak performance is noted during times of moderate arousal. Optimal arousal is necessary for achieving appropriate function for attention getting, attention holding, and attention releasing, as originally described by Cohen (1972).
On the most basic level of development, arousal and attention are best measured by tools such as the Neonatal Behavioral Assessment Scale (Brazelton, 1995). This scale includes measures of arousal, state organization, habituation, and attending. Brazelton (1995) states that certain aspects of infant functioning should only be measured when the child is in an optimal state of arousal and attending.
Similar tools are not readily available to evaluate the impact of arousal and attention on the occupational performance of older children. However, behavioral observations can be made as a part of other standardized tests.
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