The Somatosensory System or Tactile System, includes multiple types of sensation from the body - light touch, pain, pressure, temperature, and joint and muscle position sense (also called proprioception). However, these modalities are lumped into three different pathways in the spinal cord and have different targets in the brain. The first modality is called discriminative touch, which includes touch, pressure, and vibration perception, and enables us to “read” raised letters with our fingertips, or describe the shape and texture of an object without seeing it. The second grouping is pain and temperature, which is just what it sounds like, and also includes the sensations of itch and tickle. The third modality is called proprioception, and includes receptors for what happens below the body surface: muscle stretch, joint position, tendon tension, etc. This modality primarily targets the cerebellum which needs minute-by-minute feedback on what the muscles are doing.
The central nervous systems ability to process tactile sensory input is distorted in the child with SPD and causes the child great discomfort. Their brain may register even the most subtle sensations as extreme irritation or even painful and he may respond in an abnormally reactive way such as grimacing or pulling away from the stimulus.
The central nervous system must rely on five sensory nerve receptors in the skin to keep it informed about its environment. These receptors are; light touch (surface), pressure (deep), temperature (hot & cold) and pain. It is quite possible for one type of receptor to be sensitive and the other normalized. This explains why he may tolerate light touches, but dislike firm hugs; or hate tags and hair cuts.
The tactile defensive individual who experiences this extreme sensory registration can have great distress in daily living. This discomfort may be compared to the experience of trimming your fingernails too close.The raw sensation experienced by nerves that are no longer protected by the fingernail can be very irritating. This is similar to the way that a person with extreme touch sensitivity may experience sensations, except for two important differences. First, in the case of the person who just clipped their nails, the discomfort comes because the nerves that have been sheltered are now exposed making the person acutely aware of sensations he does not ordinarily feel. The nerve function is normal, but the experience is abnormal. For a person who is overly sensitive to touch the experiences are normal and the nerve function is abnormal. Second, the person who has clipped his nails will soon become accustomed to the sensation, while the person with the over sensitive system does not accommodate to the sensations no matter how much exposure he has. Because of this he may feel bombarded by dozens of unpleasant sensory experiences on a daily basis.
This child may be constantly aware of the clothes on his body to the point of distraction. He may be unable to concentrate on school work because his filtering system is not screening out the feel of the hard chair, the bumps on the pencil, the sharp edges of the paper, the air current blowing through the room, etc.This child may dread art projects that include finger-painting, glue and clay.
This child might want to dress from head to toe in soft sweat clothes, even in hot weather, as this prevents his skin from being exposed to tactile stimulation and decrease the sensory invasion of his nervous system. The slightest accidental bump from another person may feel like a threat and he may lash out in defense. It may appear that he is impulsive, hitting others, but no one understands that he is fighting against the perceived raid of his space as interpreted by his brain.
He may dislike group games like tag or dodge ball, or holding hands with a partner can be agonizing.He may be afraid of the possibility of being touched by another child. He may want to stand apart from others to prevent being bumped and this prevents him from being able to interact with friends in a normal way.
Adults who experience this type of hypersensitivity may have problems in their relationships. Even when appropriate, they still might not want to hug or hold hands with their partners. Normal daily physical contact may cause annoyance and aversion. Wanting to only talk and not touch physically can negatively impact adult relationships. Surprise touches, especially when approached from behind, can cause distress and the person may respond with a punch. The adult who has these problems probably does not intend to be withholding or withdrawn, but this is the only way his nervous system can handle personal interactions.
The individual who is tactile defensive may also experience other problems such as coordination problems, wet the bed, speech and language delays, gets dizzy easy, easily confused, overwhelmed, experience hand-eye coordination difficulties, and motor planning issues.
SIGNS OF TACTILE DYSFUNCTION:
1. HYPERSENSITIVITY TO TOUCH (tactile defensiveness):
- becomes fearful, anxious or aggressive with light or unexpected touch
- as an infant, did/does not like to be held or cuddled; may arch back, cry, and pull away
- distressed when diaper is being, or needs to be, changed
- appears fearful of, or avoids standing in close proximity to other people or peers (especially in lines)
- becomes frightened when touched from behind or by someone/something they can not see (such as under a blanket)
- complains about having hair brushed; may be very picky about using a particular brush
- bothered by rough bed sheets (i.e., if old and “bumpy”)
- avoids group situations for fear of the unexpected touch
- resists friendly or affectionate touch from anyone besides parents or siblings (and sometimes them too!)
- dislikes kisses, will “wipe off” place where kissed
- prefers hugs
- a raindrop, water from the shower, or wind blowing on the skin may feel like torture and produce adverse and avoidance reactions
- may overreact to minor cuts, scrapes, and or bug bites
- avoids touching certain textures of material (blankets, rugs, stuffed animals)
- refuses to wear new or stiff clothes, clothes with rough textures, turtlenecks, jeans, hats, or belts, etc.
- avoids using hands for play
- avoids/dislikes/aversive to “messy play”, i.e., sand, mud, water, glue, glitter, playdoh, slime, shaving cream/funny foam etc.
- will be distressed by dirty hands and want to wipe or wash them frequently
- excessively ticklish
- distressed by seams in socks and may refuse to wear them
- distressed by clothes rubbing on skin; may want to wear shorts and short sleeves year round, toddlers may prefer to be naked and pull diapers and clothes off constantly
- or, may want to wear long sleeve shirts and long pants year round to avoid having skin exposed
- distressed about having face washed
- distressed about having hair, toenails, or fingernails cut
- resists brushing teeth and is extremely fearful of the dentist
- is a picky eater, only eating certain tastes and textures; mixed textures tend to be avoided as well as hot or cold foods; resists trying new foods
- may refuse to walk barefoot on grass or sand
- may walk on toes only
2. HYPOSENSITIVITY TO TOUCH (under-responsive):
- may crave touch, needs to touch everything and everyone
- is not aware of being touched/bumped unless done with extreme force or intensity
- is not bothered by injuries, like cuts and bruises, and shows no distress with shots (may even say they love getting shots!)
- may not be aware that hands or face are dirty or feel his/her nose running
- may be self-abusive; pinching, biting, or banging his own head
- mouths objects excessively
- frequently hurts other children or pets while playing
- repeatedly touches surfaces or objects that are soothing (i.e., blanket)
- seeks out surfaces and textures that provide strong tactile feedback
- thoroughly enjoys and seeks out messy play
- craves vibrating or strong sensory input
- has a preference and craving for excessively spicy, sweet, sour, or salty foods
3. POOR TACTILE PERCEPTION AND DISCRIMINATION:
- has difficulty with fine motor tasks such as buttoning, zipping, and fastening clothes
- may not be able to identify which part of their body was touched if they were not looking
- may be afraid of the dark
- may be a messy dresser; looks disheveled, does not notice pants are twisted, shirt is half untucked, shoes are untied, one pant leg is up and one is down, etc.
- has difficulty using scissors, crayons, or silverware
- continues to mouth objects to explore them even after age two
- has difficulty figuring out physical characteristics of objects; shape, size, texture, temperature, weight, etc.
- may not be able to identify objects by feel, uses vision to help; such as, reaching into backpack or desk to retrieve an item