Example of how visual, auditory and somatosensory information merge into multisensory integration representation in the superior colliculus
Sensory processing disorder (SPD; also known as sensory integration dysfunction) is a condition that exists when multisensory integration is not adequately processed in order to provide appropriate responses to the demands of the environment.
The senses provide information from various modalities, vision, audition, tactile, olfactory, taste, proprioception, vestibular system; that humans need to function. Sensory processing disorder is characterized by significant problems to organize sensation coming from the body and the environment and manifested by difficulties in the performance in one or more of the main areas of life: productivity, leisure and play or activities of daily living. Different people experience a wide range of difficulties when processing input coming from a variety of senses, particularly tactile (p.e. finding fabrics itchy and hard to wear while others do not), vestibular (e.g. experiencing motion sickness while riding a car) and propioceptive (having difficulty grading the force to hold a pen in order to write).
Sensory integration was defined by occupational therapist Anna Jean Ayres in 1972 as "the neurological process that organizes sensation from one's own body and from the environment and makes it possible to use the body effectively within the environment".
Sensory processing disorders are classified into three broad categories: sensory modulation disorder, sensory based motor disorders and sensory discrimination disorders.
Sensory modulation disorder (SMD) consists of over-responding, or under-responding to sensory stimuli or seeking sensory stimulation. Sensory modulation refers to a complex central nervous system process by which neural messages that convey information about the intensity, frequency, duration, complexity, and novelty of sensory stimuli are adjusted. Subtypes are over-responsivity, under-responsivity and sensory craving (seeking) This group may include a fearful and/or anxious pattern, negative and/or stubborn behaviors, self-absorbed behaviors that are difficult to engage or creative or actively seeking sensation.
Sensory discrimination disorder (SDD), or incorrect processing of sensory information. Incorrect processing of visual or auditory input, for example, may be seen in inattentiveness, disorganization, and poor school performance. Subtypes are: visual, auditory, tactile, taste/smell, position/movement, interoception.
Signs and symptoms
Symptoms may vary according to the disorder's type and subtype present. SPD can affect one sense or multiple senses. While many people can present one or two symptoms, Sensory Processing Disorder has to have a clear functional impact on the person's life.
People suffering from over-responsivity might:
Dislike textures such as those found in fabrics, foods, grooming products or other materials found in daily living, to which most people would not react. This dislike interferes with normal function.
Avoid crowds and noisy places
Motion sickness (not related to other medical explanations)
Refuse normal skin contact interactions (kissing, cuddling or hugging) due to negative experience of touch sensation (not to be confused with shyness or social difficulties)
Feel seriously discomforted, sick or threatened by normal sounds, lights, movements, smells, tastes, or even inner sensations such as heartbeat.
Be picky eaters
Have sleep disorders (waking up to minor sounds, problems getting sleep because of sensory overload)
Find it difficult to self calm, feel constantly under stress
People suffering from under-responsivity:
Show extreme difficulties waking up
Appear unreactive and slow
Be unaware of pain and/or other people
Might appear deaf even when auditory function has been tested
Child might be difficult being toilet trained, unaware of being wet or soiled
People suffering from sensory craving might:
Seek or make loud, disturbing noises
Climb, jump and crash constantly
Seek "extreme" sensations
Suck on or bite clothing, fingers, pencils, etc.
People suffering from sensory motor based problems might:
Appear slow and uncoordinated
Feel clumsy, slow, poor motor skills or handwriting
Have poor posture
Poor posture with Anterior pelvic tilt
Children might be delayed in crawling, standing, walking or running.
Become verbose to avoid motor tasks
People suffering from sensory discrimination problems might:
Drop things constantly
Have poor handwriting
Difficulty dressing and eating
Use inappropriate force to handle objects
Other signs and symptoms
Poorly integrated balance and rightning reflexes
Low muscle tone patterns in extensor versus gravity and flexor versus gravity muscle systems
The mid-brain and brain stem regions of the central nervous system are early centers in the processing pathway for multisensory integration, these brain regions are involved in processes including coordination, attention, arousal, and autonomic function. After sensory information passes through these centers, it is then routed to brain regions responsible for emotions, memory, and higher level cognitive functions. Sensory Processing Disorders not only affects interpretation and reaction to stimuli at the midbrain areas, but impact several higher functions. Damage in any part of the brain involved in multisensory processing can cause difficulties to adequately process stimuli in a functional way.
Current research in sensory processing is focused on finding the genetic and neurological causes of SPD. EEG and measuring event-related potential (ERP) are traditionally used to explore the causes behind the behaviors observed in SPD. Some of the proposed underlying causes by current research are:
Differences in tactile and auditory over responsivity show moderate genetic influences, with tactile over responsivity demonstrating greater heritability. Bivariate genetic analysis suggested different genetic factors for individual differences in auditory and tactile SOR.
People with sensory over-responsivity might have increased D2 receptor in the striatum, related to aversion to tactile stimuli and reduced habituation. In animal models, prenatal stress significantly increased tactile avoidance.
Studies using event-related potentials (ERPs) in children with the sensory over responsivity subtype found atypical neural integration of sensory input. Different neural generators could be activated at an earlier stage of sensory information processing in people with SOR than in typically developing individuals. The automatic association of causally related sensory inputs that occurs at this early sensory-perceptual stage may not function properly in children with SOR. One hypothesis is that multisensory stimulation may activate a higher-level system in frontal cortex that involves attention and cognitive processing, rather than the automatic integration of multisensory stimuli observed in typically developing adults in auditory cortex.
Recent research found an abnormal white matter microstructure in children with SPD, compared to typical children and those with other neurological disorders such as autism and ADHD.
Diagnosis is primarily arrived at by the use of standardized tests, standardized questionnaires, expert observational scales, and free play observation at an occupational therapy gym. Observation of functional activities might be carried at school and home as well. Some scales that are not exclusively used in SPD evaluations are used to measure visual perception, function, neurology and motor skills.
Several therapies have been developed to treat SPD.
Sensory integration therapy
Vestibular system is stimulated through hanging equipment such as tire swings
The main form of sensory integration therapy is a type of occupational therapy that places a child in a room specifically designed to stimulate and challenge all of the senses.
During the session, the therapist works closely with the child to provide a level of sensory stimulation that the child can cope with, and encourage movement within the room. Sensory integration therapy is driven by four main principles:
Just right challenge (the child must be able to successfully meet the challenges that are presented through playful activities)
Adaptive response (the child adapts his behavior with new and useful strategies in response to the challenges presented)
Active engagement (the child will want to participate because the activities are fun)
Child directed (the child's preferences are used to initiate therapeutic experiences within the session)
Sensory processing therapy
This therapy retains all of the above-mentioned four principles and adds:
Intensity (person attends therapy daily for a prolonged period of time)
Developmental approach (therapist adapts to the developmental age of the person, against actual age)
Test-retest systematic evaluation (all clients are evaluated before and after)
Process driven vs. activity driven (therapist focuses on the "Just right" emotional connection and the process the reinforces the relationship)
Parent education (parent education sessions are scheduled into the therapy process)
"joie de vivre" (happiness of life is therapy's main goal, attained through social participation, self-regulation, and self-esteem)
Combination of best practice interventions (is often accompanied by integrated listening system therapy, floor time, and electronic media such as Xbox Kinect, Nintendo Wii, Makoto II machine training and others)
Some of these treatments (for example, sensorimotor handling) have a questionable rationale and no empirical evidence. Other treatments (for example, prism lenses, physical exercise, and auditory integration training) have had studies with small positive outcomes, but few conclusions can be made about them due to methodological problems with the studies. Although replicable treatments have been described and valid outcome measures are known, gaps exist in knowledge related to sensory integration dysfunction and therapy. Empirical support is limited, therefore systematic evaluation is needed if these interventions are used.
Children with hypo-reactivity may be exposed to strong sensations such as stroking with a brush, vibrations or rubbing. Play may involve a range of materials to stimulate the senses such as play dough or finger painting.
Children with hyper-reactivity may have trouble calming down prior to going to sleep. Exposing the child to peaceful activities such as quiet music, gentle rocking, yoga, or deep breathing in a softly lit room can help calm them and ease them to sleep.
Treats and rewards may be used to encourage children to tolerate activities they would normally avoid.
While occupational therapists using a sensory integration frame of reference work on increasing a child's ability to adequately process sensory input, other OTs may focus on environmental accommodations that parents and school staff can use to enhance the child's function at home, school, and in the community. These may include selecting soft, tag-free clothing, avoiding fluorescent lighting, and providing ear plugs for "emergency" use (such as for fire drills).
There is a growing evidence base that points to and supports the notion that adults also show signs of sensory processing difficulties. In the United Kingdom early research and improved clinical outcomes for clients assessed as having sensory processing difficulties is indicating that the therapy may be an appropriate treatment. The adult clients show a range of presentations including autism and Asperger's syndrome, as well as developmental coordination disorder and some mental health difficulties. Therapists suggest that these presentations may arise from the difficulties adults with sensory processing difficulties encounter trying to negotiate the challenges and demands of engaging in everyday life.
It is estimated that up to 16.5% of elementary school aged children present elevated SOR behaviors in the tactile and/or auditory modalities. However, this figure might represent an understimation of Sensory Over Responsivity prevalence, since this study did not include children with developmental disorders or those delivered preterm, who are more likely to present it.
This figure is, nonetheless, larger than what previous studies with smaller samples had shown: an estimate of 5–13% of elementary school aged children. Incidence for the remaining subtypes is currently unknown.
Relationship to other disorders
Because comorbid conditions are common with sensory integration issues, a person may have other conditions as well. People who receive the diagnosis of sensory integration dysfunction may also have signs of anxiety problems, ADHD, food intolerances, behavioral disorders and other disorders.
Autistic spectrum disorders and difficulties of sensory processing
Sensory processing disorder is a common comorbidity with autism spectrum disorders. Although responses to sensory stimuli are more common and prominent in autistic children and adults, there is no good evidence that sensory symptoms differentiate autism from other developmental disorders. Differences are greater for under-responsivity (for example, walking into things) than for over-responsivity (for example, distress from loud noises) or for sensory seeking (for example, rhythmic movements). The responses may be more common in children: a pair of studies found that autistic children had impaired tactile perception while autistic adults did not.
The Sensory Experiences Questionnaire has been developed to help identify the sensory processing patterns of children who may have autism.
SPD and ADHD
It is speculated that SPD may be a misdiagnosis for persons with attention problems. For example, a student who fails to repeat what has been said in class (due to boredom or distraction) might be referred for evaluation for sensory integration dysfunction. The student might then be evaluated by an occupational therapist to determine why he is having difficulty focusing and attending, and perhaps also evaluated by an audiologist or a speech-language pathologist for auditory processing issues or language processing issues. Similarly, a child may be mistakenly labeled "Attention deficit hyperactivity disorder (ADHD)" because impulsivity has been observed, when actually this impulsivity is limited to sensory seeking or avoiding. A child might regularly jump out of his seat in class despite multiple warnings and threats because his poor proprioception (body awareness) causes him to fall out of his seat, and his anxiety over this potential problem causes him to avoid sitting whenever possible. If the same child is able to remain seated after being given an inflatable bumpy cushion to sit on (which gives him more sensory input), or, is able to remain seated at home or in a particular classroom but not in his main classroom, it is a sign that more evaluation is needed to determine the cause of his impulsivity.
SPD is in Stanley Greenspan’s Diagnostic Manual for Infancy and Early Childhood and as Regulation Disorders of Sensory Processing part of the The Zero to Three’s Diagnostic Classification. but is not recognized in the manuals ICD-10 or in the recently updated DSM-5. However, unusual reactivity to sensory input or unusual interest in sensory aspects is included as a possible but not necessary criterium for the diagnosis of autism.
Researchers have described a treatable inherited sensory overstimulation disorder that meets diagnostic criteria for both attention deficit disorder and sensory integration dysfunction.
Over 130 articles on sensory integration have been published in peer-reviewed (mostly occupational therapy) journals. The difficulties of designing double-blind research studies of sensory integration dysfunction have been addressed by Temple Grandin and others. More research is needed.
Because the amount of research regarding the effectiveness of SPD therapy is limited and inconclusive, the American Academy of Pediatrics advises pediatricians to inform families about these limitations, talk with families about a trial period for SPD therapy, and teach families how to evaluate therapy effectiveness.
Sensory processing disorders were first described in-depth by occupational therapistAnna Jean Ayres (1920–1989). According to Ayres's writings, an individual with SPD would have a decreased ability to organize sensory information as it comes in through the senses.
Ayres's theoretical framework for what she called Sensory integration was developed after six factor analytic studies of populations of children with learning disabilities, perceptual motor disabilities and normal developing children. Ayres created the following nosology based on the patterns that appeared on her factor analysis:
Dyspraxia: poor motor planning (more related to the vestibular system and proprioception)
Poor bilateral integration: inadequate use of both sides of the body simultaneously
Tactile defensiveness: negative reaction to tactile stimuli
Visual perceptual deficits: poor form and space perception and visual motor functions
Somatodyspraxia: poor motor planning (related to poor information coming from the tactile and proprioceptive systems)
Both visual perceptual and auditory language deficits were thought to possess a strong cognitive component and a weak relationship to underlying sensory processing deficits, so they are not considered central deficits in many models of sensory processing.
In 1998, Mulligan performed a study on 10,000 sets of data, each representing an individual child. She performed confirmatory and exploratory factor analyses and found similar patterns of deficits with her data as Ayres did.
Dunn's nosology uses two criteria: response type (passive vs active) and sensory threshold to the stimuli (low or high) creating 4 subtypes or quadrants:
low registration, high threshold with passive response.
sensory avoiding, low threshold and active response.
sensory seeking, high threshold and active response.
sensory sensitive, low threshold with passive response.
Sensory processing model
In Miller's nosology "sensory integration dysfunction" was renamed into "Sensory processing disorder" to facilitate coordinated research work with other fields such as neurology since "the use of the term sensory integration often applies to a neurophysiologic cellular process rather than a behavioral response to sensory input as connoted by Ayres."  The current nosology of sensory processing disorders was developed by Miller, based on neurological underlying principles.
A wide variety of approaches have incorporated sensation in order to influence learning and behavior.
The Alert Program for Self-Regulation is a complementary approach that encourages cognitive awareness of alertness often with the use of sensory strategies to support learning and behavior.
Other approaches primarily use passive sensory experiences or sensory stimulation based on specific protocols, such as the Wilbarger Approach and the Vestibular-Oculomotor Protocol.
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