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Children who have autism spectrum disorders (ASDs) exhibit impairments in communication and social skills and have restrictive or repetitive interests that limit functioning.
and sensory processing disorder (SPD) is correlated with many diagnostic symptoms of autism and levels of everyday functioning. Better understanding by medical professionals of the impact of SPD and the resources available for identification and treatment may lead to increased functioning and participation for children with autism and their families.
SPD defined
Sensory processing is defined as the brain’s ability to register, organize, and make sense of information received from one’s senses.
Although most children with autism exhibit symptoms of SPD, this condition is also common in children who have other developmental disabilities and may occur in typically developing children.
When sensory processing is dysfunctional, the individual may struggle with behaving in line with the demands of the environment, contributing to broader functional difficulties.
Sensory integration dysfunction: this term was used previously to describe the dysfunctional motor, behavioral, emotional, and attentional responses to sensation that were caused, theoretically, by the brain’s inability to process tactile, visual, olfactory, gustatory, proprioceptive, and/or visual information. The recommended term used to describe this dysfunction is SPD.
SPD: this condition includes sensory-based processing challenges that result in behavioral dysfunction. The condition encompasses impaired processing that affects the ability to modulate (sensory modulation disorders), motor plan (sensory-based motor disorders), and discriminate between the qualities of sensation (sensory discrimination disorders).
Sensory defensiveness: also called sensory overresponsivity. Individuals with this condition have a low threshold for sensation that causes them to avoid or overreact to sensory information. This condition includes tactile defensiveness, gravitational insecurity (extreme sensitivity to vestibular information), and auditory defensiveness.
Occupational therapy–sensory integration: this therapy uses a sensory integration approach to remediate dysfunction associated with SPDs.
To increase diagnostic precision for research and treatment purposes, a unified nosology has been proposed for the discussion of sensory processing dysfunction.
In this nosology, several categories of SPD have been suggested to describe different patterns of behavioral dysfunction: sensory-based motor disorder, sensory discrimination disorder (SDD), and sensory modulation disorder.
Their hierarchical relationships are illustrated in Fig. 1. Sensory-based motor disorder is described as poor motor planning and/or postural instability resulting from ineffectual processing of information from the senses and can present as discoordinated or immature movement patterns. SDD is described as the inability to interpret differences and similarities between information received from the senses. For example, difficulty discriminating visual information may present with inability to distinguish between letters, making acquisition of reading skills a challenge. Sensory modulation disorders are described later and are of particular relevance to a discussion on children with autism.
(From Miller LJ, Anzalone ME, Lane SJ, et al. Concept evolution in sensory integration: a proposed nosology of diagnosis. Am J Occup Ther 2007;61(2):137; with permission.)
Sensory modulation disorder constitutes a cluster of disorders characterized by impairment in the intensity and nature of behavior in response to sensory input.
As a result, the response to sensation is out of synchrony with the demands of the environment, and attentional and emotional regulation is affected. Three subcategories of sensory modulation disorder have been hypothesized: sensory overresponsivity, sensory underresponsivity, and sensory seeking. Although these subcategories are currently hypothetical, physiologic research is emerging to support these distinctions.
Sensory overresponsivity is the subtype of sensory modulation disorder that is characterized by fast, intense, sustained reaction to sensory stimuli that is out of proportion with the situation.
People with sensory overresponsivity are hypothesized to have an unusually low threshold for sensation in any or all of the sensory systems (tactile, vestibular, proprioceptive, visual, olfactory, gustatory, and/or auditory).
As a result, people with sensory overresponsivity may overreact to sensations that are typically not perceived as threatening or even noticed by most people. Symptoms may include inappropriate behavioral outbursts that may be triggered by the feeling of textures on skin (clothing, socks, food on fingertips), movement activities (swinging, riding in the car), and loud or unexpected noises (bell ringing at school, toilet flushing). Often, children with sensory overresponsivity seem to be excessively cautious, become upset with changes in routine, and have difficulty with transitions between activities. These automatic and inappropriate responses prevent effective functioning in daily life tasks. Sensory overresponsivity is often most evident when the person is faced with unexpected or novel situations or during transitions from one activity to another. Insistence on sameness and difficulty in discontinuing or initiating an activity are common behaviors in children with autism that may be related to dysfunctional sensory processing.
Is there a relationship between restricted, repetitive, stereotyped behaviors and interests and abnormal sensory response in children with autism spectrum disorders?.
Symptoms might include not responding when name is called, extreme preference for sedentary activities, and failing to respond to pain. The lack of ability to register sensation may lead to a child being described as unresponsive or unaware of their surroundings, both common concerns in children with autism.
Children with sensory seeking may also engage in dangerous movement activities not in line with their motor skill level or demonstrate disruptive behavior that limits their ability to integrate into classroom or group situations. Sensory-seeking behavior has the potential to cause injury and disrupt the development of meaningful routines and relationships. This could be particularly problematic in children with autism who already have difficulty with relationship formation.
Sensory processing abilities and their relation to participation in leisure activities among children with high-functioning autism spectrum disorder (HFASD).
Sensory modulation disorders of any type can be disruptive to a child’s development. Children with ASD demonstrate high levels of sensory modulation disorders across ages and severity of autism.
The presentation of these symptoms is heterogeneous, with highest incidence of sensory underresponsivity followed by overresponsivity and sensory seeking. Links between sensory modulation disorders and psychological dysfunction may contribute to autism symptom severity and deficits in everyday functioning, in effect, compounding the severity of autism symptoms.
Investigation into the underlying neurologic causes of sensory modulation disorders are ongoing, with significant discoveries emerging. Technological advances have made it possible to measure physiologic functioning related to the behavior observed in response to sensory input. The research into the physiologic correlates of sensory modulation disorders can provide insight into this comorbid condition.
Physiologic evidence for distinction of sensory modulation disorders
In the 1970s, Jean Ayres was one of the first to describe what seemed to be a sympathetic nervous system fight-or-flight reaction to sensation for children demonstrating difficulty modulating their arousal level.
Physiologic measurement tools are now available that make it possible to explore the neurologic correlates of sensory modulation disorder. Using tools such as electrodermal sensors, research is beginning to capture the physiologic response of individuals with behavioral abnormalities to sensory information, implicating the autonomic nervous system in this dysfunction. Two key studies point to differences in sympathetic and parasympathetic response to sensation for children with clinically identified sensory modulation disorder compared with children developing typically.
In a study of the physiologic responses to sensation in children clinically identified with sensory modulation disorder, McIntosh and colleagues
demonstrated connections between different patterns of sensory processing, electrodermal responses (EDR), and functional behavior. The researchers chose EDR as the objective physiologic measure of sympathetic nervous system activity based on prior research that had shown associations of EDR activation with startling or threatening stimuli and during positive and negative emotional events. EDR changes were measured for the study in the context of an innovative space ship–themed protocol, dubbed the Sensory Challenge Protocol, which was designed to present sensory stimulus in a nonthreatening manner. Each of the sensory modalities was stimulated during the protocol (eg, tactile stimulus, feather touched to the skin; vestibular stimulus, child tipped back in the chair; olfactory, smell of wintergreen under nose; auditory and visual, series of bright lights and sounds). The physiologic responses of children who had been identified clinically as having sensory modulation disorder were compared with those of children without such a diagnosis.
The study revealed that there were significantly more children in the sensory modulation disorder group who failed to exhibit EDR response to stimuli than in the typically developing group. This finding tentatively points to a decrease in sympathetic nervous system response in children with sensory underresponsivity. The children who did not respond to the stimulus were then removed from the next analysis. Physiologic evidence for the overresponsivity pattern of dysfunction was provided with the greater response and higher number of responses to sensation in the remaining sensory modulation disorder group. These findings provided physiologic support for the distinction between sensory underresponsivity and sensory overresponsivity. Specifically, as expected, there was both a decrease and an increase in EDR response to sensory stimuli in children with sensory modulation disorder consistent with the clinical presentation of sensory underresponsivity and overresponsivity compared with typically developing children.
These data provided support for the unique physiologic pattern of processing sensory information in children clinically diagnosed with sensory modulation disorder and served as the basis for additional research into the nature and causes of sensory modulation disorder.
A subsequent study provided evidence for indirect implication of the sympathetic nervous system and involvement of the parasympathetic system. Schaaf and colleagues
conducted a pilot study of differences in parasympathetic functioning of children with clinical symptoms of sensory modulation disorder that were age matched to children functioning typically. They used the cardiac vagal tone index as the primary measure of parasympathetic activity based on its demonstrated validity in a variety of clinical populations and age groups for this purpose. Data on cardiac vagal tone were collected during the Sensory Challenge Protocol described earlier.
The results indicated that children with sensory modulation disorder had significantly lower cardiac vagal tone measurements, suggesting that these children have less effective parasympathetic functioning compared with typical controls.
The investigators discussed the implications of sensory modulation disorder on functioning, suggesting that a compromised parasympathetic system may disrupt the child’s ability to maintain a calm focused state in the face of sensations encountered in everyday life.
Impact of sensory modulation disorders on functioning for children with ASD
The functional difficulties associated with the diagnostic symptoms of autism pose daily obstacles for many children. The presence of sensory modulation disorders in these individuals is correlated with and may compound the symptoms of autism. If the child’s sympathetic and parasympathetic systems are not working to allow the maintenance of a calm alert state, this may make participation in meaningful daily activities an even greater challenge.
Sensory modulation disorders, which are associated with many of the symptoms of autism, may compound dysfunction and further decrease life engagement. This includes the relationship between sensory modulation disorders and diagnostic features of autism, such as restrictive/repetitive behaviors and social skill deficits as well as comorbid feeding dysfunction.
Restrictive and Repetitive Behavior
Restricted repetitive behaviors (RRBs) are included as one component of the diagnostic criteria for autism
It has been suggested that these dysfunctional, repetitive, and inappropriate behaviors may represent an effort to relieve stress produced by difficulty in processing sensory information.
Lower-order RRBs include stereotypy, such as hand flapping or self-injurious behavior (eg, head banging, scratching, or biting). These behaviors can be found in children with severe developmental disabilities as well as autism.
These behaviors encompass compulsions, insistence on sameness, and restricted interests. Children with autism sometimes have odd attachments to and/or unusual preoccupation with objects (eg, fascination with spinning the wheels on a toy truck or gazing at ceiling fans). They also can have a narrow range of interests and compulsively try to steer conversation to discussion of these interests. These behaviors can restrict participation in functional activities.
Several studies have provided growing evidence that sensory modulation disorders are highly correlated with and may contribute to the frequency and severity of RRBs.
Is there a relationship between restricted, repetitive, stereotyped behaviors and interests and abnormal sensory response in children with autism spectrum disorders?.
examined the relationships between SPD and stereotyped movement in 221 children with and without developmental disorders (including autism). The researchers used the Short Sensory Profile (SSP) to measure SPD, Stereotyped and Self-Injurious Movement Interview, and Repetitive Behavior Interview to measure potentially related behaviors. They found that the within-group and between-group differences in stereotyped movement could be accounted for by differences in SSP scores.
This relationship between sensory modulation disorders and RRBs may be especially strong for sensory overresponsivity. Chen and colleagues
looked at the relationship between the SSP and the Childhood Routines Inventory (measuring compulsivelike behaviors) in 29 children diagnosed with high functioning autism or Asperger syndrome. The investigators found a significant relationship between the frequency and intensity of behaviors in the Childhood Routines Inventory and tactile, visual, and auditory sensitivity (all constructs included in sensory overresponsivity).
found that children with autism and intellectual disability were significantly more sensitive to sensation and went to greater means to avoid sensation than children with intellectual disability alone. The investigators combined these results with a previous study of the same participants that revealed that stereotyped repetitive behaviors of children with autism are commonly associated with anxiety. The combined results suggested that the use of RRBs might be a result of the child’s effort to relieve anxiety produced by sensory input.
Using repetitive motor movement or demonstrating the need to control the conversation may be an effort to reduce feelings of anxiety resulting from discomfort with sensory stimulation. RRBs can lead to a lack of flexibility and isolation that limits the play repertoire and opportunity to engage with others.
and, here too, the presence of sensory modulation disorders may further amplify these deficits. Several studies have described links between deficits in social competence and/or decreased social participation and sensory modulation disorders. Hilton and colleagues,
for example, found a strong relationship between sensory responsivity and social responsiveness, irrespective of the child’s intelligence quotient score. This relationship was particularly true for the proximal (ie, tactile, oral, and olfactory sense items) and multisense items. The investigators suggested that this made sense given the multisensory and proximal nature of communication and socialization. Similarly, Lane and colleagues
found a clear association between sensory processing dysfunction and impairments in communicative skills. Children with autism and sensory modulation disorders participate less frequently in activities outside the school and home settings and report enjoying those activities less than children with autism who have less prominent sensory modulation deficits.
Sensory processing abilities and their relation to participation in leisure activities among children with high-functioning autism spectrum disorder (HFASD).
Meaningful social engagement is one hallmark of satisfaction with life. Sensory modulation disorders may exacerbate the social deficits found in autism and present increased challenges for the development of meaningful socialization.
Feeding and Eating
Children with ASD frequently demonstrate dysfunction in feeding and eating (ie, food selectivity), and it has been suggested in the literature that this may be related to sensory modulation disorders as well, specifically sensory overresponsivity. In the population of children with autism, 40% to 60% of children have food selectivity, meaning they have a restricted range of foods that they will eat.
Clinicians and parents describe children with autism who choose foods based on their presentation and texture. For example, some children with autism only eat foods of a particular texture, color, or flavor; off a particular plate; and/or with certain utensils.
suggested that food selectivity might be partially a result of sensory modulation disorders. This is in keeping with the fact that children with sensory overresponsivity but who were otherwise developing typically were found in one study
to eat fewer fresh fruits and vegetables and gagged more when eating than those without sensory modulation disorders. Also, children with autism often are very particular about the texture of foods,
which may implicate a lower threshold for sensation in the tactile system. Further investigation is needed to establish the factors associated with food selectivity in the autistic population, including close examination of the link to sensory modulation disorder.
Summary
Sensory modulation disorders have been associated with key diagnostic features of autism and comorbid feeding dysfunction. Researchers and clinicians are just beginning to understand the role of the autonomic nervous system in the behavioral manifestation of sensory modulation disorders in the autistic population. In addition to the functional deficits caused by the symptoms of autism, if the child is unable to maintain physiologic homeostasis due to sensory modulation disorders, little energy may be available for participation in meaningful functional activities that are the cornerstone of quality of life.
When to refer
From time to time, all children experience some difficulty modulating their arousal level in response to sensation from the environment.
When typically developing children are stressed, tired, or overwhelmed, they may tune out or act out when faced with sensory experiences that they usually handle in their stride. However, when a child consistently has a behavioral response to stimuli that is extreme and inconsistent with the demands of the environment, a referral for treatment may be indicated. Children on the autism spectrum, in particular, should be referred as soon as possible so that intervention can begin early. Attending to warning signs (Table 1) can allow for the provision of treatment for possible increases in functioning.
Beyond informal observation, the SSP is a quick and easy screening tool that can help to confirm clinical observations that point to a sensory modulation disorder.
This caregiver questionnaire has 38 items and takes approximately 10 minutes to administer. Using a Likert scale, parents report the frequency of the occurrence of behaviors related to sensory dysfunction. The measure yields results that quantify no, probable, or definite differences in the behavioral output in response to sensory stimulus compared with typically developing children. Knowing the warning signs and investigating further with screening tools can facilitate appropriate referrals to clinicians, such as occupational therapists (OTs), who have training to treat sensory modulation disorders.
Table 1Examples of behaviors associated with sensory modulation disorders
Sensory Overresponsivity
Sensory Underresponsivity
Sensory Seeking
Is upset by tags in clothing and the seam in socks and/or only wears clothing with particular textures Struggles excessively to avoid grooming tasks such as brushing teeth or having nails clipped Hates messy play (eg, finger painting). Becomes very concerned when hands get dirty Covers ears and/or becomes very distressed with loud or unexpected noises Avoids movement activities such as swinging or climbing Is picky about food textures and frequently gags on food or the smell of nonpreferred food Has extreme difficulty with changes in routine, novel activities, and anything unexpected
Does not respond when name is called repeatedly Does not react to injuries and seems to have a very high pain tolerance Often appears disheveled and does not notice food left on face or clothing twisted on body Difficulty with toilet training and has frequent accidents Extreme preference for sedentary activities Does not notice things going on around the room Overstuffs food in mouth
Is in motion from the moment of waking until falling into bed to sleep at night Takes risks during play such as climbing too high, jumping off high surfaces, and moving too quickly for safety Appears driven to touch everything in the environment Frequently crashes and bumps into people and objects Mouths nonfood objects Makes nonfunctional noises Likes spicy or flavorful foods
The treatment includes several overlapping and integrated elements. Components of treatment include remediation for underlying sensory processing dysfunction, environmental modifications to reduce sensory stressors in the environment, and task practice to increase competence in specific skill areas.
Each of these components is addressed briefly in the sections that follow.
Remediation
To remediate the underlying deficits related to sensory modulation disorders, the OT seeks to integrate the client’s sensory system through response to multisensory activities that get increasingly more difficult as the child gains skill. This approach, often called Occupational Therapy–Sensory Integration (OT-SI) has a specific set of elements that must be present for fidelity to be maintained.
The treatment should be designed to involve active client participation in activities that provide enhanced sensation and require the client’s adaptive response. Activities should be client driven and support optimal arousal, leading to the client’s ability to self-regulate during the experience of sensation. Motivation for participation is encouraged through the therapeutic relationship, collaboration on activity choice, and a play context. The child is set up for success and assisted to learn through experiences with sensory stimuli. Through these activities, the goal is for the child to learn to respond appropriately to a variety of sensory stimuli.
Environmental Modification and Tools for Adaptation
In addition to remediation of underlying sensory dysfunction, several other treatment elements may be aimed at increasing functioning of individuals with autism and sensory modulation disorder. OTs, speech and language pathologists, physical therapists, special education teachers, parents, and others may be involved in aspects of treatment of sensory modulation disorders beyond the remedial sensory integration approach.
Different environments (eg, home, school) hold different challenges. In collaboration with parents, the clinician or teacher can provide recommendations for environmental modifications to minimize sensory challenges and capitalize on the child’s strengths.
For example, a child with sensory overresponsivity often has extreme difficulty with changes in routine, making a class field trip very difficult. To decrease the stress associated with this experience, the therapist may write a story describing what the child should expect during the trip,
offer calming music to listen to on the bus ride, and allow the child to take a break in a quiet space with a trusted adult when the experience becomes overwhelming. Environment modifications and support may allow for greater participation in meaningful activities for the child with autism and sensory modulation disorders.
Specific Task Practice
After providing remediation to minimize underlying deficits and modifying the environment to increase the child’s comfort and success, task practice may be necessary for specific skill development.
For example, a child with sensory modulation disorder and autism may have been uncomfortable with sensations associated with self-care tasks and lacked the attention required to practice these skills. As a result, they may experience lack of development in this area. Treatment of sensory modulation disorders requires specific task practice (eg, zipping coat, tying shoes, brushing teeth) using a multisensory approach to increase skill in specific areas.
Sensory Integration Treatment Research
Sensory integration treatment is one of the most frequently used therapies for autism and sensory modulation disorders.
Despite the frequency of use, however, little evidence is available, and there are no adequate-sized high-quality randomized controlled trials to confirm the effectiveness of this approach. Research on OT-SI and associated components described previously for sensory modulation disorders has suffered from lack of uniform terminology, lack of fidelity to sensory integration theory, lack of homogeneity of treatment groups, and lack of sample sizes large enough to detect changes.
Efforts are underway to address these issues. Studies are emerging that use manualized treatment approaches administered by adequately trained providers to ensure that important elements of treatment are upheld.
Better inclusion and exclusion criteria are being developed to ensure that samples include subjects who experience similar dysfunction. For example, Miller and colleagues
completed a pilot randomized control design with the treatment group participating in OT-SI and controls including an activities placebo group and wait-list group. Homogeneous samples were obtained using several clinical measures and physiologic data (ie, EDR to stimuli) to verify sensory modulation dysfunction. Despite the small sample size, the OT-SI group was shown to achieve statistically significant improvement on a measure of goal attainment and on a parental report measure of attention and social skills. High-quality research on the sensory integration treatment approach is emerging, but much work is still needed to determine conclusively the efficacy of this approach.
Summary
Children with autism experience many challenges that affect their ability to function. SPD and, specifically, sensory modulation disorder can compound dysfunction and further inhibit participation in productive activities. Through detection of and referral for sensory modulation disorders, treatment can be accessed. Emerging treatment evidence points to functional gains for autism and sensory modulation disorder that can ease the burden that this combination of symptoms has on the everyday life of children with autism.
References
American Psychiatric Association
Diagnostic and statistical manual of mental disorders.
(Text Revision)4th edition. American Psychiatric Association,
Washington, DC2000
Is there a relationship between restricted, repetitive, stereotyped behaviors and interests and abnormal sensory response in children with autism spectrum disorders?.
Sensory processing abilities and their relation to participation in leisure activities among children with high-functioning autism spectrum disorder (HFASD).
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