Definition of SPD

Sensory processing refers to the way the nervous system receives messages from the senses and turns them into responses. For those with Sensory Processing Disorder, sensory information goes into the brain but does not get organized into appropriate responses. Those with SPD perceive and/or respond to sensory information differently than most other people. Unlike people who have impaired sight or hearing, those with Sensory Processing Disorder do detect the sensory information; however, the sensory information gets “mixed up” in their brain and therefore the responses are inappropriate in the context in which they find themselves.

Sensory Processing Disorder or SPD (originally called Sensory Integration Dysfunction) is a neurological disorder in which the sensory information that the individual perceives results in abnormal responses. A more formal definition is: SPD is a neurophysiologic condition in which sensory input either from the environment or from one’s body is poorly detected, modulated, or interpreted and/or to which atypical responses are observed. Pioneering occupational therapist, psychologist, and neuroscientist A. Jean Ayres, Ph.D., likened SPD to a neurological “traffic jam” that prevents certain parts of the brain from receiving the information needed to interpret sensory information correctly.

The Eight Sensory Systems.

There are eight sensory systems:

Pioneering occupational therapist, psychologist, and neuroscientist A. Jean Ayres, Ph.D., likened SPD to a neurological “traffic jam” that prevents certain parts of the brain from receiving the information needed to interpret sensory information correctly.
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Prevalence of SPD: How often does it occur?

Sensory Processing Disorder can affect anyone. Studies indicate that 5% to 16% of children exhibit symptoms of SPD.

(Ahn, Miller et. al., 2004; Ben-Sasoon, Carter et. al., 2009)
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Causes of SPD.

The exact cause of Sensory Processing Disorder has not yet been identified. Preliminary studies and research suggest that SPD is often inherited. Prenatal and birth complications have also been implicated as causal in SPD, as well as certain environmental factors. A summary of research into the causes and prevalence of SPD is included in Sensational Kids: Hope and Help for Children With Sensory Processing Disorder (2005) written by Founder and current Executive Director of the SPD Foundation, Lucy Jane Miller Ph.D., OTR
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Subtypes of SPD, Red Flags, and Symptoms of each Subtype

Pattern 1: Sensory Modulation Disorder

Sensory Over-Responsive
Sensory Under-Responsive
Sensory Craving
Pattern 2: Sensory-Based Motor Disorder

Postural Disorder
Pattern 3: Sensory Discrimination Disorder

SPD may occur in each sensory system: Visual, Auditory, Tactile, Smell, Taste, Vestibular, Proprioception, Interoception

The symptoms of SPD vary greatly depending upon the sense that is affected, how that sense is affected, and the severity of the condition.

People with SPD misinterpret everyday sensory information, such as touch, sound, and movement. They may feel bombarded by information, they may seek out intense sensory experiences, or they may be unaware of sensations that others feel. They may also have sensory-motor symptoms such as a weak body, clumsiness or awkwardness or delayed motor skills.

If a person has SPD often the symptoms result in emotional, behavioral, social, attentional, or motoric problems.

Our current knowledge suggests that there are six subtypes of SPD. Almost all individuals with SPD have a combination of symptoms from more than one subtype. The chart below shows the three major patterns and the six subtypes of SPD.

Summary of Sensory Processing Disorder Subtypes

Primary Pattern Subtype Description
Sensory Modulation Disorder Difficulty regulating responses to sensory stimuli
Sensory Over-Responsive Predisposition to respond too much, too soon, or for too long to sensory stimuli most people find quite tolerable
Sensory Under-Responsive Predisposition to be unaware of sensory stimuli, to have a delay before responding, responses are muted or responds with less intensity compared to the average person
Sensory Craving Driven to obtain sensory stimulation, but getting the stimulation results in disorganization; and does not satisfy the drive for more
Sensory-Based Motor Disorder Difficulty with balance, motor coordination, and the performance of skilled, non-habitual and/or habitual motor tasks
Postural Disorder poor perception of position of body position; poorly developed movement patterns that depend on core stability. Thus, appears weak and/or has poor endurance
Dyspraxia Difficulty thinking of, planning and/or executing skilled movements especially novel movement patterns
Sensory Discrimination Disorder Difficulty interpreting subtle qualities of objects, places, people or other environments
Auditory DD Difficulty interpreting characteristics of sensory stimuli that is heard
Visual DD Difficulty determining/interpreting characteristics of sensory stimuli that is seen
Tactile DD Difficulty determining/interpreting characteristics of sensory stimuli that is felt on the skin
Vestibular DD Difficulty interpreting characteristics of sensory stimuli, experienced through movement of the body through space or against gravity
Proprioceptive DD Difficulty determining/interpreting characteristics of sensory stimuli experienced through use of the muscles and joints
Gustatory DD Difficulty determining/interpreting characteristics of sensory stimuli that is tasted
Olfactory DD Difficulty determining/interpreting characteristics of sensory stimuli that is smelled
Pattern 1: Sensory Modulation Disorder

Sensory Over-Responsivity

Individuals with sensory over-responsivity are more sensitive to sensory stimulation than most people. Their bodies feel sensation too easily or too intensely. They might feel as if they are being constantly bombarded with information. Consequently, these people often have a “fight or flight” response to sensation e.g. being touched unexpectedly or loud noise, a condition sometimes called “sensory defensiveness.” They may try to avoid or minimize sensations, e.g., withdraw from being touched, or cover their ears to avoid loud sounds.

Sensory Under-Responsivity

Individuals who are under-responsive to sensory stimuli are often quiet and passive, disregarding or not responding to stimuli of the usual intensity available in their sensory environment. They may appear withdrawn, difficult to engage and or self absorbed because they do not detect the sensory input in their environment. Their under-responsivity to tactile and deep pressure input may lead to poor body awareness, clumsiness or movements that are not graded appropriately. These children may not perceive objects that are too hot or cold or they may not notice pain in response to bumps, falls, cuts, or scrapes.

Sensory Craving

Individuals with this pattern actively seek or crave sensory stimulation and seem to have an almost insatiable desire for sensory input. They tend to be constantly moving, crashing, bumping, and/or jumping. They may “need” to touch everything and be overly affectionate, not understanding what is “their space” vs. “other’s space”. Sensory seekers are often thought to have Attention Deficit Hyperactivity Disorder (ADHD) and Attention Deficit Disorder (ADD).

Pattern 2: Sensory-Based Motor Disorder

Postural Disorder

An individual with postural disorder has difficulty stabilizing his/her body during movement or at rest in order to meet the demands of the environment or of a motor task. When postural control is good, the person can reach, push, pull, etc. and has good resistance against force. Individuals with poor postural control often do not have the body control to maintain a good standing or sitting position.

Dyspraxia/Motor Planning Problems

Individuals with Dyspraxia have trouble processing sensory information properly, resulting in problems planning and carrying out new motor actions. They may have difficulty in forming a goal or idea, planning a sequence of actions or performing new motor tasks. These individuals are clumsy, awkward, and accident-prone. They may break toys, have poor skill in ball activities or other sports, or have trouble with fine motor activities. They may prefer sedentary activities or try to hide their motor planning problem with verbalization or with fantasy play.
Sensory Discrimination Disorder

Sensory discrimination refers to the process whereby specific qualities of sensory stimuli are perceived and meaning attributed to them. Discriminate means understanding accurately what is seen, heard, felt, tasted, or smelled. Individuals with SDD difficulties have problems determining the characteristics of sensory stimuli. The result is a poor ability to interpret or give meaning to the specific qualities of stimuli, or difficulty detecting similarities and differences among stimuli. (Do I see a “P” or a “Q”? Do I hear “cat” or “cap”? Do I feel a quarter or a dime in my pocket? Am I falling to the side or backwards?). Individuals with poor sensory discrimination may appear awkward in both gross and fine motor abilities and/or inattentive to people and objects in their environment. They may take extra time to process the important aspects of sensory stimuli.

Eight Sensory Systems

(Please note: figures below are from Wikipedia)


The five basic sensory systems:

3. Olfactory (smell) System
4. Gustatory (taste) System
5. Tactile System
The three sensory systems Ayres focused on in describing sensory integration dysfunction:

5. Tactile System (see above)
6. Vestibular (sense of head movement in space) System
7. Proprioceptive (sensations from muscles and joints of body) Syssetm
The most recently discussed set of sensations related to internal organs

8. Interoception

A. The five basic sensory systems:

1. Visual System

The visual system is responsible for seeing.

The primary visual area of the brain is the occipital lobe (see figure). Projections are received from the retina (through the thalamus) where different types of information are encoded. Types of visual information include: color, shape, orientation, and motion. From the ventral stream in the occipital lobe information projects to the temporal lobe to process what objects are. From the dorsal stream, information goes to the parietal lobes to process where objects are located.

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2. Auditory System

The auditory system is responsible for hearing.

The primary auditory cortex is located in the superior temporal gyrus of the brain (see figure). Specific sound frequencies can be mapped precisely onto the primary auditory cortex. Particular areas in the auditory cortex process changes in sound frequency or amplitude, while other areas process combinations of sound frequencies. The major area involved in comprehending language, (called Wernike’s area) is located in the left hemisphere in most people.

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3. Olfactory (smell) System

The olfactory system is responsible for processing smell.

The olfactory bulb is located in the most forward part of the brain on the bottom side of the brain (see figure). The olfactory bulb transmits smell information from the nose to the brain, and is thus necessary for a proper sense of smell. Unlike the other sensory systems the olfactory bulb has only one source of sensory input (neurons of the olfactory epithelium) and one output. Thus it is assumed to be more of a filter than an associative circuit that has many inputs and many outputs.

The olfactory bulb does receive “top-down” information from areas such as the amygdala, neocortex, hippocampus, and others. It has four functions:

▪ discriminating among odors

▪ enhancing detection of odors

▪ filtering out many background odors

▪ allowing higher brain areas related to arousal and attention to modify the detection and/or the discrimination of odors

Looking up from the base of the brain

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4. Gustatory (taste) System

The Gustatory system is responsible for the sense of taste.

It allows us to discriminate between safe and harmful foods. Usually individuals prefer sweet and salty tastes to sour or bitter tastes. Detecting salt is critical to keeping a regulated and stable internal body environment. This taste is perceived positivity because it facilitates re-uptake of water into the blood. Since it helps survival, salt is perceived as a pleasant taste by most humans.

Sour taste can be good in small quantities, but when it gets too sour it becomes unpleasant to taste. This has occurred through evolution to protect us from eating over-ripe fruit, rotten meat, and other spoiled foods (dangerous because of bacteria which grow in these environments)..

The bitter taste is almost completely unpleasant to humans. This is because many dangerous pharmacological agents taste bitter, including caffeine, nicotine, and strychnine. Some bitter tastes can be overcome (note how popular Starbucks is world wide! Also note how many medicines when chewed, have a bitter taste, apparently being interpreted by our bodies as poisons.

Sweet taste signals that carbohydrates are present. Carbohydrates have a high calorie count and are desirable (humans in the distant past did not know when their next meal would occur, so they evolved to want/need to eat sweet tastes.

The primary gustatory cortex is located near the somatotopic region for the tongue, in the insular cortex deep in the lateral fissure with the secondary taste areas in the opercula (see figure). This means the location is folded deeply within the cortex within the lateral sulcus between the temporal and frontal lobes.

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5. Tactile System

The tactile system is responsible for processing touch information from the body.

The body sends tactile information to the somatosensory cortex through neural pathways to the spinal cord, the brain stem, and the thalamus. The primary somatosensory cortex is the primary receptive area for touch sensations and is located in the lateral postcentral gyrus, a prominent structure in the parietal lobe of the human brain.

Due to its many connections to other brain areas, the somatosensory cortex is the part of the nervous system that integrates touch, pressure, temperature, and pain.

The tactile system is extremely important in SPD. Many individuals with the disorder have tactile symptoms such as tactile defensiveness or under-responsivity to touch and pain. The touch system is one of the three foundational systems used in sensory integration treatment.

B. The three sensory systems Ayres focused on in describing the treatment of sensory integration dysfunction:

5. Tactile system (see description above)

6. Vestibular System

The vestibular system contributes to balance and orientation in space. It is the leading system informing us about movement and position of head relative to gravity.

Our movements include two positions rotations and linear directionality. Thus, the vestibular system has two related components: the semicircular canal system, (related to detecting rotation) and the otoliths, (related to detecting linear acceleration/deceleration).

The vestibular system sends signals primarily to the neural parts of the brain that control our eye movements, and that keep us upright.

The vestibular system contains three semicircular canals, which are approximately at right angles to each other:

the horizontal canal, which detects rotation around a vertical axis (as when you do spins in ice skating)

the anterior semicircular canal , detects movement in forward/backward plane as in a nodding movement,

the posterior canal, detects movement in a frontal plane as in when cartwheeling.

The canal on each side has an almost parallel counterpart on the other side. Each pair of canals works in a push-pull fashion: when one is stimulated, its partner is inhibited. Together the partners allow us to sense rotation in all directions.

Emphasis on the function of the vestibular system comes from Ayres influence when she identified sensory processing disorders as a new condition. This sensory system has a broad influence in many parts of the brain projecting to:

The cerebellum (to effect movements of the head, eyes, and posture).
Cranial nerves III, IV, and VI (to permit the eyes to fix on a moving object while staying in focus).
Reticular formation (to signal how to adjust circulation and breathing when the body assumes a new position).
Spinal Cord (to allow quick reflex reactions related to balancing).
Thalamus (to control head and body motor responses.
The information above is only a simple introduction to the role of the vestibular system as it relates to SPD. The figure below depicts the complex vestibular system. This figure is in the public domain from Grey’s anatomy book.

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7. Proprioception

Proprioception (sense of muscle and/or joint movements) System

The proprioceptive system (sometimes abbreviated as “prop” by therapists when they talk about it) senses the position, location, orientation, and movement of the body muscles and joints. Proprioception provides us with the sense of the relative position of neighboring parts of the body and effort used to move body parts.

Proprioception is activated by input to a proprioceptor in the periphery of the body. The proprioceptive sense combines sensory information from neurons in the inner ear (detecting motion and orientation) and stretch receptors in the muscles and the joint-supporting ligaments for stance.

Two types of proprioception exist:

Conscious proprioception, which travels up the posterior column-medial lemniscus pathway to the cerebrum; and
Unconscious proprioception which travels up the dorsal spinocerebellar tract,[20] to the cerebellum.
Proprioception was felt by Ayres to be the foundation (with vestibular impairments) of SPD. It is one of the three sensory systems used by SI trained therapists as the cornerstone of the sensory aspect of advanced treatment.

Temporary proprioceptive impairment is reported during times of quick growth, mostly during adolescence. Other large increases or drops in bodyweight/size due to fluctuations of fat (e.g., liposuction) and/or muscle content (e.g., body-building) also affect proprioception.

Proprioception is occasionally impaired in typically developing individuals, for example, if you are tired. Generally speaking we do not notice out proprioceptive sense because we disregard through habituation, desensitization, or adaptation sensory stimuli that is continuously present. In essence, the habituation makes the proprioceptive sensory impressions disappear. One practical advantage of this is that unnoticed sensation continue in the background while an individual’s attention can move to another concern.

Temporary impairment of proprioception has also been known to occur from an overdose of vitamin B6 and or by cytotoxic factors such as chemotherapy.

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8. Interoception

The eighth, often neglected, but frequently problematic sensory system in SPD is the Interoceptive System. Interoception refers to sensations related to the physiological / physical condition of the body. ‎ Interoceptors are internal sensors that provide a sense of what our internal organs are feeling. Hunger and thirst are examples of interoception.

Interoception detects responses that guide regulation, including hunger, heart rate, respiration and elimination. The Interoceptive stimulation is detected through nerve endings lining the respiratory and digestive mucous membranes. Interoception works the vestibular and proprioceptive senses to determine how an individual perceives their own body. Well-modulated interoception helps the individual detect proprioceptive and vestibular sensation normally. For example, if a person feels his/her heart pounding, while it is not comfortable, trauma from the stimulation is not likely; nor will the stimulation be craved. The same is true for hunger and thirst, as well as the feeling of the need to urinate or have a bowel movement.

Interoception is associated with autonomic motor control, and is different than mechano-reception (in the skin) and proprioception (in the muscles and joints). Interoception is located in the dorsal posterior insula and it create s distinct feelings from the body including pain, temperature, itch, muscular and visceral sensations, vasomotor activity, hunger, thirst, and the need for air. In humans, the primary Interoceptive activity occurs in the right anterior insula, which provides the basis for subjective feelings of ones’ emotional awareness.

Some researchers believe that our perceptions of well-being, energy and stress are based on sensations representing the physiological condition of our bodies. They suggest that interoception is a foundation subjective feelings, emotion and self-awareness. There is evidence that the anterior insula-cingulate system may integrate Interoceptive information with emotional salience to form a subjective representation of the body; while the mid-cingulate cortex, are more likely involved in environmental monitoring, response selection, and body orientation. (see Taylor KS, Seminowicz DA, Davis KD. (2009). Two systems of resting connectivity in Human Brain Mapp. 30(9):2731-45

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__________________________________________________ __________________

See below for general diagram of the neuroanatomical locations noted in above descriptions. The brains depicted below are shown from a side view with the nose pointing to the left.

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__________________________________________________ __________________

Sensory Processing Disorder Checklist

Many of the symptoms listed in the following categories are common to that particular age group. Where more than a few symptoms are found in a child, we recommend you talk to your doctor or check the SPD Foundation’s Treatment Directory for a professional experienced with treating Sensory Processing Disorder.*

Infant/ Toddler Checklist:
____ My infant/toddler has problems eating.
____ My infant/toddler refused to go to anyone but me.
____ My infant/toddler has trouble falling asleep or staying asleep
____ My infant/toddler is extremely irritable when I dress him/her; seems to be uncomfortable in clothes.
____ My infant/toddler rarely plays with toys, especially those requiring dexterity.
____ My infant/toddler has difficulty shifting focus from one object/activity to another.
____ My infant/toddler does not notice pain or is slow to respond when hurt.
____ My infant/toddler resists cuddling, arches back away from the person holding him.
____ My infant/toddler cannot calm self by sucking on a pacifier, looking at toys, or listening to my voice.
____ My infant/toddler has a “floppy” body, bumps into things and has poor balance.
____ My infant/toddler does little or no babbling, vocalizing.
____ My infant/toddler is easily startled.
____ My infant/toddler is extremely active and is constantly moving body/limbs or runs endlessly.
____ My infant/toddler seems to be delayed in crawling, standing, walking or running.

Pre-School Checklist:
____ My child has difficulty being toilet trained.
____ My child is overly sensitive to stimulation, overreacts to or does not like touch, noise, smells, etc.
____ My child is unaware of being touched/bumped unless done with extreme force/intensity.
____ My child has difficulty learning and/or avoids performing fine motor tasks such as using crayons and fasteners on clothing.
____ My child seems unsure how to move his/her body in space, is clumsy and awkward.
____ My child has difficulty learning new motor tasks.
____ My child is in constant motion.
____ My child gets in everyone else’s space and/or touches everything around him.
____ My child has difficulty making friends (overly aggressive or passive/ withdrawn).
____ My child is intense, demanding or hard to calm and has difficulty with transitions.
____ My child has sudden mood changes and temper tantrums that are unexpected.
____ My child seems weak, slumps when sitting/standing; prefers sedentary activities.
____ It is hard to understand my child’s speech.
____ My child does not seem to understand verbal instructions.

School Age:
___ My child is overly sensitive to stimulation, overreacts to or does not like touch, noise, smells, etc.
___ My child is easily distracted in the classroom, often out of his/her seat, fidgety.
___ My child is easily overwhelmed at the playground, during recess and in class.
___ My child is slow to perform tasks.
___ My child has difficulty performing or avoids fine motor tasks such as handwriting.
___ My child appears clumsy and stumbles often, slouches in chair.
___ My child craves rough housing, tackling/wrestling games.
___ My child is slow to learn new activities.
___ My child is in constant motion.
___ My child has difficulty learning new motor tasks and prefers sedentary activities.
___ My child has difficulty making friends (overly aggressive or passive/ withdrawn).
___ My child ďgets stuck’ on tasks and has difficulty changing to another task.
___ My child confuses similar sounding words, misinterprets questions or requests.
___ My child has difficulty reading, especially aloud.
___ My child stumbles over words; speech lacks fluency, and rhythm is hesitant.

___ I am over-sensitive to environmental stimulation: I do not like being touched.
___ I avoid visually stimulating environments and/or I am sensitive to sounds.
___ I often feel lethargic and slow in starting my day.
___ I often begin new tasks simultaneously and leave many of them uncompleted.
___ I use an inappropriate amount of force when handling objects.
___ I often bump into things or develop bruises that I cannot recall.
___ I have difficulty learning new motor tasks, or sequencing steps of a task.
___ I need physical activities to help me maintain my focus throughout the day.
___ I have difficulty staying focused at work and in meetings.
___ I misinterpret questions and requests, requiring more clarification than usual.
___ I have difficulty reading, especially aloud.
___ My speech lacks fluency, I stumble over words.
___ I must read material several times to absorb the content.
___ I have trouble forming thoughts and ideas in oral presentations.
I found this here

I found the part about the vestibular system interesting because I know somebody with a thalamus stroke who has a head tilt. I thought the article might be interesting to the people here.