Tactile Defensiveness Vs Tactile Discrimination

Protective System (Dysfunction causes Tactile Defensiveness) 

Skin has an important function - protection. It acts as a physical barrier between us and the world. Our skin can feel too hot and cold sensations’ and respond accordingly, for example, on being pricked by a needle we are hurt and brain perceives pain sensation. For detailed description of Tactile Defensiveness click here

This system helps us in identifying light touch, crude touch, pain and
temperature which are protective in nature. When a needle is inserted in baby's buttocks for vaccination he feels uneasy and painful due to which he may cry aloud, this pain sensation happens due to protective touch system. Touch is the first sensation that starts developing in womb at five weeks. Protective system works phenomenally in a newborn, which helps him to react towards changes in temperature, come in contact with his or her mother and feel secure in her arms. It helps in sucking mother’s nipple to take the feed and feel her body’s warmth and cosiness. Due to this, children clasp fingers and toes when being touched.

When child tries to stand on his own feet however falls back due to lack of balance and postural control, he feels distressed and cries, since he feels pain in his buttocks or legs. The protective system supports child to sense the pain and discomfort. Similarly, dirty diapers make child uneasy and, colic pain (prominent from 0-6 Months) can cause too much of discomfort and distress.

Neuroscience Background:

According to A. Jean Ayres (1972), tactile defensiveness is the response that occurs, when Dorsal Column-Medial Lemniscus (DCML) Pathway fails to exert inhibitory influence over Anterolateral (AL) Pathway.This means that DCML system does not work properly and hence AL system predominates on it due to which child reacts adversely, negatively on being touched, hugged or kissed.
The child has difficulties in hair washing, tooth brushing and nail cutting or avoids being touched reflecting Tactile DefensivenessChild shows dislike towards parents or caregiver’s hugs, kisses or arm around the shoulder by either pushing or asking not to touch him.They don't like being messy or touching objects like glue, paints, shaving form or cream, shampoo, bubble bath.

Treatment Strategies:

Weighted Items: Wearing weighted vests, backpacks or hats can have calming effect in school. Great range of weighted items are available on Amazon such as ankle weights, lap weights shoulder and neck weights.

Heavy Work/Resistive activities: These activities have calming effect on brain. The muscles and ligaments work against the gravity proving deep-firm pressure to the body.

Brushing: Sensations received from clothes or their tags can be disrupting in nature. An Occupational Therapist (OT) may guide parents in administering the Wilbarger Brushing Protocol which reduces tactile defensiveness.It is designed a particular fashion to reduce tactile defenesivemess.The brushing is done in specific sequence at specific intervals throughout the day.  

Vibration: Vibrators can be useful around arms and legs however should be applied under supervision of Occupational Therapist who is Sensory Integration trained. It is another form of deep pressure that activates proprioceptors (receptors in muscles and ligaments). The adverse effects which will be immediately visible are dizziness, headache or nausea.

Tactile Discrimination System (Dysfunction causes Tactile Discrimination difficulties)

This system is fast, efficient and its development is essential for dextrous tasks and In-Hand-Manipulation. Discriminative system is associated with function of discrimination, such as exploring the world and differentiate between different types of touches such as type of texture, and size of object. For example, consider how easily we can differentiating between different size coins in our pocket without looking at them. Opening or closing the lid of jar or doing small buttons without actually looking at shirt are examples of Tactile Discrimination and in hand Manipulation. He might not react at all towards injuries, may have lack of body awareness. 
This system also responds to vibration, touch pressure and deep pressure
information. As the child achieves developmental milestones they also develop a sense of touch discrimination. As the child grows older his abilities of discriminating tools objects and toys improve gradually. 
In a normal developmental process, as the child grows and he develops fine motor skills ability to discriminate different fabrics (soft blanket or stuff toy and wooden surface), sizes (small and large Lego pieces) develop. They enjoy jumping on soft mattress bed rather than playing on the wooden floor with carpet. 
So if the child’s cluster of behaviours such as being accident prone, dropping things from hand, difficulties in managing buttons, zippers, laces and ties, difficulties in handwriting it may be considered that these activities are linked to dysfunction in tactile discrimination.

Neuroscience Background:

Discriminative system is associated with function of tactile discrimination such as detection of size, form, texture as well as movement across the skin as evidenced by Fisher and Bundy (1991). The dorsal column medial leminiscus (DCML) pathway and associated receptors are responsible to respond to stimuli transmitting vibratory, touch pressure, discriminatory and deep pressure information meaning for appropriate functioning of Discriminative system DCML system is responsible.
When there is damage in DCML pathway, the sensory feedback to higher brain centres (cortex) is interrupted leading to deterioration of coordinated fine motor abilities of child.  This can be evidenced with empirical research work done by Cohen (1999), who concluded that injury to DCML can lead to decreased sensory feedback to the cortex causing uncoordinated fine motor skills. Therefore, child has difficulties in carrying out fine motor activities such as doing laces, buttons, fastening zippers.