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CHAPTER III

RELATED LITERATURE

This chapter consists of overview and related literatures related to ADHD,

causes of ADHD, relationship between vestibular system & sensory processing

and ADHD intervention, which is divided in to following sub topics:

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3.1 Causes of ADHD

3.2 Diagnostic criteria for ADHD

3.3 Types of ADHD

3.4 Role of vestibular system in sensory processing

3.5 Relationship between Sensory processing and ADHD

3.6 Intervention for ADHD

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Attention deficit hyperactivity disorder (ADHD) is a neurobiological

disorder that affects the emotions, behavior, and cognitive state of 4%7% of

children worldwide (Spencer, Biederman, & Mick, 2007). Symptoms include

inattention, impulsivity, and hyperactivity, and they often persist into adulthood.

The longterm emotional, social, educational, and occupational implications of

ADHD are profound and well documented (Cermak, 2005). It is the most

commonly studied and diagnosed psychiatric disorderin children, affecting

about 3 to 5 percent of children globally and is diagnosed in about 2 to 16

percent of school-aged children.It is a chronic disorder with 30 to 50 percent of

those individuals diagnosed in childhood continuing to have symptoms into
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adulthood. Adolescents and adults with ADHD tend to develop coping

mechanisms to compensate for some or all of their impairments.It is estimated

that between two and five percent of adults live with ADHD. ADHD is diagnosed

two to four times more frequently in boys than in girls. Its symptoms can be

difficult to differentiate from other disorders, increasing the likelihood that the

diagnosis of ADHD will be missed.

2.1 Causes of ADHD:

ADHD has traditionally been viewed as a problem related to attention,

stemming from an inability of the brain to filter competing sensory inputs such

as sight and sound. Recent research, however, has shown that children with

ADHD do not have difficulty in that area. Instead, researchers now believe that

children with ADHD are unable to inhibit their impulsive motor responses to

such input (Barkley, 1997; 1998a). It is still unclear what the direct and

immediate causes of ADHD are, although scientific and technological advances

in the field of neurological imaging techniques and genetics promise to clarify

this issue in the near future. Most researchers suspect that the cause of ADHD

is genetic or biological, although they acknowledge that the childs environment

helps determine specific behaviors.

(a) Brain dysfunction:

Current research indicates the frontal lobe, basal ganglia, caudate

nucleus, cerebellum, as well as other areas of the brain, play a significant role

in ADHD because they are involved in complex processes that regulate

behavior (Teeter, 1998). These higher order processes are referred to as
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executive functions. Executive functions include such processes as inhibition,

working memory, planning, self-monitoring, verbal regulation, motor control,

maintaining and changing mental set and emotional regulation. According to a

current model of ADHD developed by Dr. Russell Barkley, problems in

response inhibition is the core deficit in ADHD. This has a cascading effect on

the other executive functions listed above (Barkley, 1997).

(b) Heredity:

Heredity is the most common cause of ADHD. Most of research about

the heritability of ADHD comes from family studies, adoption studies, twin

studies and molecular genetic research.

Family Studies: If a trait has a genetic basis we would expect the rate

of occurrence to be higher with the biological family members (e.g., brown-eyed

people tend to have family members with brown eyes). Dr. Joseph Biederman

(1990) and his colleagues at the Massachusetts General Hospital have studied

families of children with ADHD. They have learned that ADHD runs in families.

They found that over 25% of the first-degree relatives of the families of ADHD

children also had ADHD, whereas this rate was only about 5% in each of the

control groups. Therefore, if a child has ADHD there is a five-fold increase in

the risk to other family members.

Adoption Studies: If a trait is genetic, adopted children should

resemble their biological relatives more closely than they do their adoptive

relatives. Studies conducted by psychiatrist Dr. Dennis Cantwell compared

adoptive children with hyperactivity to their adoptive and biological parents.


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Hyperactive children resembled their biological parents more than they did their

adoptive parents with respect to hyperactivity.

Twin Studies: Another way to determine if there is a genetic basis for a

disorder is by studying large groups of identical and non-identical twins.

Identical twins have the exact same genetic information while non-identical

twins do not. Therefore, if a disorder is transmitted genetically, both identical

twins should be affected in the same way and the concordance ratethe

probability of them both being affectedshould be higher than that found in

non-identical twins. There have been several major twin studies in the past few

years that provide strong evidence that ADHD is highly heritable. They have

had remarkably consistent results in spite of the fact that they were done by

different researchers in different parts of the world. In one such study, Dr.

Florence Levy and her colleagues studied 1,938 families with twins and siblings

in Australia. They found that ADHD has an exceptionally high heritability as

compared to other behavioral disorders. They reported an 82 percent

concordance rate for ADHD in identical twins as compared to a 38 percent

concordance rate for ADHD in non-identical twins.

Molecular Genetic Research: Twins studies support the hypothesis of

the important contribution that genes play in causing ADHD, but these studies

do not identify specific genes linked to the disorder. Genetic research in ADHD

has taken off in the past five years. This research has focused on specific

genes that may be involved in the transmission of ADHD. Dopamine genes

have been the starting point for investigation. Two dopamine genes, DAT1 and

DRD4 have been reported to be associated with ADHD by a number of


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scientists. Genetic studies revealed promising results, and we should look for

more information about this soon.

(c) Exposure to Toxic Substances:

Researchers have found an association between mothers who smoked

tobacco products or used alcohol during their pregnancy and the development

of behavior and learning problems in their children. A similar association

between lead exposure and hyperactivity has been found, especially when the

lead exposure occurs in the first three years. Nicotine, alcohol, and lead can be

toxic to developing brain tissue and may have sustained effects on the behavior

of the children exposed to these substances at early ages.

2.2 Diagnostic criteria for ADHD:

I. A) Six or more of the following symptoms of inattention have

persisted for at least six months to a degree that is maladaptive and

inconsistent with the developmental level:

Inattention

1. Often does not give close attention to details or makes careless

mistakes in schoolwork, work, or other activities.

2. Often has trouble keeping attention on tasks or play activities.

3. Often does not seem to listen when spoken to directly.


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4. Often does not follow instructions and fails to finish schoolwork, chores,

or duties in the workplace (not due to oppositional behavior or failure to

understand instructions).

5. Often has trouble organizing activities.

6. Often avoids, dislikes, or doesn't want to do things that take a lot of

mental effort for a long period of time (such as schoolwork or

homework).

7. Often loses things needed for tasks and activities (e.g. toys, school

assignments, pencils, books, or tools).

8. Is often easily distracted.

9. Is often forgetful in daily activities.

B.Six or more of the following symptoms of hyperactivity-impulsivity

have been present for at least 6 months to an extent that is disruptive and

inappropriate for developmental level:

Hyperactivity

1. Often fidgets with hands or feet or squirms in seat.

2. Often gets up from seat when remaining in seat is expected.

3. Often runs about or climbs when and where it is not appropriate

(adolescents or adults may feel very restless).

4. Often has trouble playing or enjoying leisure activities quietly.


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5. Is often "on the go" or often acts as if "driven by a motor".

6. Often talks excessively.

Impulsivity

1. Often blurts out answers before questions have been finished.

2. Often has trouble waiting one's turn.

3. Often interrupts or intrudes on others (e.g., butts into conversations or

games).

II. Some symptoms that cause impairment were present before age 7

years.

III. Some impairment from the symptoms is present in two or more settings

(e.g. at school/work and at home).

IV. There must be clear evidence of significant impairment in social, school,

or work functioning.

V. The symptoms do not happen only during the course of a Pervasive

Developmental Disorder, Schizophrenia, or other Psychotic Disorder.

The symptoms are not better accounted for by another mental disorder

(e.g. Mood Disorder, Anxiety Disorder, Dissociative Disorder, or a

Personality Disorder).

2.3 Types of ADHD:

Based on DSM IV criteria , three types of ADHD are identified.


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1. ADHD, Combined Type:

If both criteria Inattention and Hyperactive-Impulsivity are met for

the past 6 months

2. ADHD, Predominantly Inattentive Type:

If criterion Inattention is met but criterion Hyperactivity-Impulsivity

is not met for the past six months

3. ADHD, Predominantly Hyperactive-Impulsive Type:

If Criterion Hyperactivity-Impulsivity is met but Criterion Inattention

is not met for the past six months.

2.4 Role of vestibular system in sensory processing:

Ayres has postulated that the vestibular system exerts important

influence on sensory integration because it is one of the earliest neuronal

systems to develop and because it has multiple connections throughout the

nervous system. This system has many interconnections with almost every

other part of the brain. The vestibular system has among its functions the

maintenance of equilibrium, direction of eye gaze, and maintenance of a plane

of vision dependent upon head position. These are primarily made possible by

vestibular system modification of underlying muscle tone, and through

neuromuscular reflexes. In its operation, the system helps the organism to

know whether various sensory stimuli are associated with body movements or

with environmental factors. Motor function and enhanced body awareness is

affected by the vestibular systems role in facilitating impulse flow from the

muscle spindle. Information from the vestibular end-organs, the extra-ocular


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muscles and vision help individuals to distinguish whether their head is moving,

their eyes are moving or that something in the environment is moving.

Coordinated movement is thus dependent upon vestibular sensory input.

The main functions of the Vestibular system include:

1. Postural tone, extensor muscle tone, neck contraction, equilibrium

reactions, righting reactions and postural background movements as part of

the Postural System. Postural responses provide background for more

skilled and planned activity

2. Compensatory Eye Movements, stabilisation of the visual field, spatial

perception as part of the Visual System.

3. Body Scheme and the orientation of ones body to the environment

4. Autonomic Nervous System (ANS)

5. Modulation/Arousal: Modulation is the process of increasing or reducing

a neural activity to keep that activity in harmony with all the other

functions of the nervous system. The vestibular system contributes a

considerable amount to the energising/activating/exciting or

inhibiting/calming properties of the Reticular Activating System. When

facilitatory and inhibitory forces acting on the vestibular system are not in

balance, disorganisation occurs.

6. The Lymbic System is the part of the cerebral hemispheres that

generates emotionally based behaviour. Gravitational security, which

results from a well integrated vestibular system, is a foundation upon

which we build our interpersonal relationships. If a childs relationship to

the earth is not secure, then a lot of other relationships fail to develop

optimally.


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7. Influences of the digestive tract: When there is more vestibular input that

the brain can organise, the digestive centres is the brainstem become

disorganised. This stops movement of food through the digestive tract

and causes a feeling of nausea. Children who process vestibular input

inefficiently also frequently have difficulty in developing bowel and

bladder control.

Neuro-Anatomical Overview of the Vestibular System

The vestibular system is a bilateral system, each side consisting of the

peripheral end-organ, the vestibular part of the eighth cranial nerve, the

vestibular nuclei and the vestibular afferents and efferents. The peripheral end-

organ is part of the inner ear, specifically the three semicircular canals, the

utricle and the saccule. According to another source, this system is known to

perform three major functions in man: control of posture, control of eye

movements and conscious perception of space. The Vestibular receptors are

hair cells in two structures within the inner ear. The one type of receptor that is

situated in the Otolith organs, responds to linear movement and the force of

gravity. These receptors consist of tiny calcium carbonate crystalsattached to

hairlike neurons. Gravity pulls these crystals downward to press on and move

hairlike cells, which then activates the nerve fibres on the vestibular nerve.

This nerve carries vestibular input to the vestibular nuclei of the brain stem.

Because gravity is always present, the gravity receptors send a perpetual

stream of vestibular messages. When the head moves in any direction that

changes the pull of gravity upon the calcium carbonate crystals, the vestibular

input from the gravity receptors changes the information in the vestibular

system. The gravity receptors are also sensitive to bone vibration that shakes


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the crystals. The second type of vestibular receptor lies in the semicircular

canals. These receptors respond to angular movement of the head and

responds best to transient, quick movements. The activity of these receptors

provides tonic input to the central nervous system about movement and the

position of the head in space. These pathways projects to the vestibular nuclei

in the brainstem, and from there to the

Cerebellum for ongoing control of eye and head movements and

posture.These connections with the reciprocal which means that not only

does the vestibular system send information to the cerebellum, but the

connection is being reciprocated by information form the cerebellum.

Oculomotor nuclei for fixing of the eyes as the head and body moves.

This is the underlying of the vestibular-ocular reflex and nystagmus

Spinal Cord, as it influences the muscle tone and is responsible for

ongoing postural adjustments in response to how the body is moving

Thalamus and Cortex where the integration with somatosensory inputs

takes place which plays a significant role in the individuals perception of

motion and spatial orientation.( Nancy Raubenheimer, 2009)

A child with a vestibular hyposensitivity will need stronger input and will

seek more extreme motion such as fast and high swinging, roller coasters, and

strong bouncing. The input, though extreme to a normal sensory system, may

register as mild or normal to the hyposensitive child, who may be characterized

as a thrill-seeker. Symptoms of mild attentional difficulties can be exacerbated

when paired with underlying sensory issues, but hyperactivity can also be


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reduced with vestibular stimulation (Dunn & Bennett, 2002 (out of order in

references)).

2.5 Relationship between Sensory Processing and Attention

Deficit Hyperactivity disorder:

Sensory processing is the ability to respond appropriately to neural

stimuli, and Sensory Processing Disorder (SPD), also known as Sensory

Integration Dysfunction (SID), occurs when the process of regulating and

organizing sensory input is impaired, (Miller, Anzalone, Lane, Cermak, & Osten,

2007 (et al.)). Information is sensed normally but perceived abnormally. With

Attention Related Difficulties (ARD), the efficiency of the executive function

(controlling activation, focus, effort, emotion, memory, and action) is decreased

and neural circuitry is impaired (Brown, 2007). Disturbances in the prefrontal

cortex could explain clusters of related symptoms of motor difficulties and

ADHD (Cruddace & Riddell, 2006). Its not surprising that about 50% of children

with ARD also exhibit difficulty regulating and organizing sensory information

and have motor control problems (Mangeot, 2001 (listed differently in

regferences); Pitcher, Piek & Hay 2003; Yochman, 2006 Mangeot, 2001 (listed

differently in regferences).

The sensory processing and attention mechanisms of the brain are the

same (Dunn & Bennett, 2002) and integration of the vestibular, tactile, and

proprioceptive senses leads to the ability to organize, concentrate, and to

exhibit self-control (Ayers, 2005). Many of the symptoms of SPD are also

underlying neurological factors related to ADHD, indicating co-morbidity (Dunn


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& Bennett, 2002; Harvey & Reid, 2003; Mangeot, et al., 2001). Given these

factors, supporting and developing the sensory system is likely to have a

positive effect on the symptoms of ADHD

2.6 Intervention for ADHD:

a) Behavioural Approaches:

Behavioural approaches represent a broad set of specific interventions

that have the common goal of modifying the physical and social environment to

alter or change behaviour (AAP, 2001). They are used in the treatment of

ADHD to provide structure for the child and to reinforce appropriate behaviour.

Those who typically implement behavioural approaches include parents as well

as a wide range of professionals, such as psychologists, school personnel,

community mental health therapists, and primary care physicians. Types of

behavioral approaches include behavioral training for parents and teachers (in

which the parent and/or teacher is taught child management skills), a

systematic program of contingency management (e.g. positive reinforcement,

time outs, response cost, and token economy), clinical behavioral therapy

(training in problem-solving and social skills), and cognitive-behavioral

treatment (e.g., self-monitoring, verbal self-instruction, development of problem-

solving strategies, self-reinforcement) (AAP, 2001; Barkley, 1998b; Pelham,

Wheeler, & Chronis, 1998). In general, these approaches are designed to use

direct teaching and reinforcement strategies for positive behaviors and direct

consequences for inappropriate behaviour. Of these options, systematic

programs of intensive contingency management conducted in specialized

classrooms and summer camps with the setting controlled by highly trained


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individuals have been found to be highly effective (Abramowitz, et al., 1992;

Carlson, et al., 1992; Pelham & Hoza, 1996). A later study conducted by

Pelham, Wheeler, and Chronis (1998) indicates that two approachesparent

training in behavior therapy and classroom behavior interventionsalso are

successful in changing the behavior of children with ADHD. In addition, home-

school interactions that support a consistent approach are important to the

success of behavioral approaches.

The research results on the effectiveness of behavioral techniques are

mixed. While studies that compare the behavior of children during periods on

and off behavior therapy demonstrate the effectiveness of behavior therapy

(Pelham & Fabiano, 2001), it is difficult to isolate its effectiveness. The

multiplicity of interventions and outcome measures makes careful analysis of

the effects of behavior therapy alone, or in association with medications, very

difficult (AAP, 2001). A review conducted by McInerney, Reeve, and Kane

(1995) confirms that the effective education of children with ADHD requires

modifications to academic instruction, behavior management, and classroom

environment. Although some research suggests that behavioral methods offer

the opportunity for children to work on their strengths and learn self-

management, other research indicates that behavioral interventions are

effective but to a lower degree than treatment with psychostimulants (Jadad,

Boyle, & Cunningham, 1999; Pelham, et al., 1998).

b)Pharmacological Approaches :

Pharmacological treatment remains one of the most common, yet most

controversial, forms of ADHD treatment. It is important to note that the decision

to prescribe any medicine is the responsibility of medicalnot educational


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professionals, after consultation with the family and agreement on the most

appropriate treatment plan. Pharmacological treatment includes the use of

psychostimulants, antidepressants, anti-anxiety medications, antipsychotics,

and mood stabilizers (NIMH, 2000). Stimulants predominate in clinical use and

have been found to be effective with 75 to 90 percent of children with ADHD

(DHHS, 1999). Stimulants include Methylphenidate (Ritalin),

Dextroamphetamine (Dexedrine), and Pemoline (Cylert). Other types of

medication (antidepressants, anti-anxiety medications, antipsychotics, and

mood stabilizers) are used primarily for those who do not respond to stimulants,

or those who have coexisting disorders.

Researchers believe that psychostimulants affect the portion of the brain

that is responsible for producing neurotransmitters. Neurotransmitters are

chemical agents at nerve endings that help electrical impulses travel among

nerve cells. Neurotransmitters are responsible for helping people attend to

important aspects of their environment. The appropriate medication stimulates

these underfunctioning chemicals to produce extra neurotransmitters, thus

increasing the childs capacity to pay attention, control impulses, and reduce

hyperactivity. Medication necessary to achieve this typically requires multiple

doses throughout the day, as an individual dose of the medication lasts for a

short time (1 to 4 hours). However, slow- or timed-release forms of the

medication (for example, Concerta) may allow a child with ADHD to continue to

benefit from medication over a longer period of time. Doctors, teachers, and

parents should communicate openly about the childs behavior and disposition

in order to get the dosage and schedule to a point where the child can perform

optimally in both academic and social settings, while keeping side effects to a


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minimum. If it is determined that the child should receive medication during the

school day, it is important to develop a plan to ensure that medication is

administered in accordance with the plan. Although the positive effects of the

stimulant medication are immediate, all medications have side effects.

Adjusting the dosage of the medicine can diminish some of these side effects.

Some of the more common side effects include insomnia, nervousness,

headaches, and weight loss. In fewer cases, subjects have reported slowed

growth, tic disorders, and problems with thinking or with social interaction

(Gadow, Sverd, Sprafkin, Nolan, & Ezor, 1995). Medication also can be

expensive, depending upon the medicine prescribed, the frequency of

administration, and the subsequent frequency of refills. Stimulant medicines do

not normalize the entire range of behavior problems, and children under

treatment may still manifest higher levels of behavioral problems than their

peers (DHHS, 1999). Nonetheless, the American Academy of Pediatrics (AAP)

finds that at least 80 percent of children will respond to one of the stimulants if

they are administered in a systematic way. Under medical care, children who

fail to show positive effects or who experience intolerable side effects on one

type of medication may find another medication helpful. The AAP reports that

children who do not respond to one medication may have a positive response

to an alternative medication, and concludes that stimulants may be a safe and

effective way to treat ADHD in children (AAP, 2001).

c) Multimodal Approaches:

Research indicates that for many children the best way to mitigate

symptoms of ADHD is the use of a combined approach. The Multimodal

Treatment Study of Children with ADHD (MTA)is the longest and most


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thorough study of the effects of ADHD interventions (MTA Cooperative Group,

1999a, 1999b). The study followed 579 children between the ages of 7 and 10

at six sites nationwide and in Canada. The researchers compared the effects of

four interventions: medication provided by the researchers, behavioral

intervention, a combination of medication and behavioral intervention, and no-

intervention community care (i.e., typical medical care provided in the

community). Of the four interventions investigated, the researchers found that

the combined medication/behavior treatment and the medication treatment

work significantly better than behavioral therapy alone or community care alone

at reducing the symptoms of ADHD. Multimodal treatments were especially

effective in improving social skills for students coming from high-stress

environments and children with ADHD in combination with symptoms of anxiety

or depression. The study revealed that a lower medication dosage is effective

in multimodal treatments, whereas higher doses were needed to achieve

similar results in the medication-only treatment.

Researchers found improvement in the following areas after using a

multimodal intervention: child anxiety, academic performance, oppositional

behavior, and parent-child interaction. Positive results also were found in

school-related behavior when multimodal treatment is coupled with improved

parenting skills, including more effective disciplinary responses, and

appropriate reinforcements (Hinshaw, et al., 2000). These findings were

replicated across all six research sites, despite substantial differences among

sites in their samples sociodemographic characteristics. The studys overall

results appear to apply to a wide range of children and families identified as in

need of treatment services for ADHD (NIMH, 2000). Other studies demonstrate


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that multimodal treatments hold value for those children for whom treatment

with medication alone is not sufficient (Klein, Abikoff, Klass, Ganeles, Seese, &

Pollack, 1997).

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