Sensory modulation disorder (SMD) refers to difficulty regulating responses to sensory stimulation.
Back in 1972, occupational therapist and advocate Dr. A. Jean Ayers described sensory integration 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 with the environment.” Modern leaders in the field have taken the original neurological understanding and theory base of Dr. Ayers and have refined and expanded it to include sensory processing disorders.
Recommended course: Sensory Processing Differences in Children With Autism Spectrum Disorders 2nd Edition
Classifying sensory processing disorders
Researcher Lucy J. Miller classifies sensory processing disorders into three categories: sensory modulation disorder (SMD), sensory-based motor disorder (SBMD) or sensory discrimination disorder (SDD). (Galiana-Simal, Vela-Romero, Romero-Vela, Tercero, Benito-Castellanos, Muñoz-Martinez, Beato-Fernandez, 2020).
Sensory modulation disorder (SMD) refers to difficulty regulating responses to sensory stimulation. A child can overreact to a certain sensation, underreact to certain sensations and/or crave a certain sensation (Galiana-Simal, et al., 2020).
The most prominent sensory-craving behaviors are for vestibular and proprioceptive input. These are the children in constant motion, who can’t sit still and climb up on and then jump off their furniture at home. These children tend to be risk takers.
Sensory-based motor disorder applies when children have difficulties with balance, motor coordination and/or the performance of any skilled motor task. This can manifest as difficulties with motor planning, postural and bilateral coordination (Galiana-Simal, et al., 2020). Children who present with sensory-based motor disorders will often have difficulties coordinating both sides of their bodies and “timing.”
For instance, it will be difficult for them to not only coordinate their bodies to catch a ball, but to anticipate when to move their bodies or their hands in order to catch the ball. Often, these children bring their hands up in the proper position too late as the ball sails past them.
These children will also have a difficult time keeping rhythm, e.g. clapping their hands, tapping their foot to the beat of the music, or moving their bodies rhythmically to the same beat of the music is a challenge. Overall, smooth, coordinated movement is difficult for these children.
Examples of SDD
A person with SDD will have a difficult time identifying the source of a sensation (Galiana-Simal, et al., 2020). Feeling “hangry” is an example of SDD. The person will feel “out of sorts” but won’t be able to distinguish whether it is physiological (hungry) or emotional (angry, sad etc.).
Another example would be difficulty distinguishing between letters in words and identifying various sounds and from which direction they come. When someone’s tactile system can’t discriminate properly, they will typically be clumsy. All three of these sensory conditions can occur independently or concurrently.
Contemporary developments
Occupational therapist Dr. Roseann C. Schaaf established a classification system based on the Sensory Integration Test and the Sensory Integration and Praxis Test. The two large categories are sensory perception and sensory reactivity. Sensory perception is divided into somatodyspraxia (SD), visuodyspraxia (VP), and vestibular and bilateral integration deficits (VBID) (Galiana-Simal, et al., 2020).
- Somatodyspraxia (SD) is a pattern associated with poor sensory perception (especially tactile) combined with signs of poor motor planning involving the imitation, planning, and sequencing of actions. This is commonly known as motor planning deficits.
- Visuodyspraxia (VP) involves poor visual perception with poor visual-motor skills and planning. Vestibular and bilateral integration (VBID) deficits involve poor vestibular processing along with difficulties with muscle tone, postural and ocular-motor control, balance, midline integration and bilateral coordination (Galiana-Simal, et al., 2020).
Sensory reactivity refers to an excessive response or reaction to sensory input that interferes with participation in daily activities. Children may have limited diets, only wear certain fabrics, are impulsive, get in trouble in school, can’t sit still, etc.
Sensory reactivity can also manifest as the fight, flight, or freeze reaction and may produce anxiety, high activity level or inattention. Again, children can be hyper-responsive or hypo-responsive to sensory input. Sensory reactivity is often ascertained through a child’s behavior (Galiana-Simal, et al., 2020).
Biomarkers
Any type of sensory processing disorder is typically identified through the child’s behavior. Current research seeks to identify biomarkers for SPD. A 2010 study revealed that children who had a diagnosis of SPD also had lower basal activity of their parasympathetic nervous system compared to typical development (Schaaf et al., 2010).
Another 2011 study utilized electroencephalography. In this study, children with a diagnosis of SPD showed unique patterns of brain processing as measured by EEG than those of typically developing children.
This study also discovered a significant relationship between neurophysiological measures and functional performance in sensory and motor tasks between the groups (Gavin et al., 2011).
Treatment of sensory processing disorders
No matter what type of disorder, parents bring their children to occupational therapists for treatment because their children are having a difficult time with life. In Sensory Integration: Theory and Practice, the authors write:
Sensory integrative therapy is characterized by enhanced sensations gained through active engagement in meaningful activities (i.e. play) …The essence of sensory integrative therapy is that enhanced sensation, derived from active movement, when carefully matched to a child’s needs and state, (a) helps with the regulation of arousal and to support engagement and (b) enhances body schema and postural control for improved motor planning. (Bundy & Lane, 2020, p. 302)
Inherent in sensory integrative therapy is the meaningfulness of the activities for the child, and play. Sensory Integration: Theory and Practice, defines play as follows:
Play is a transaction that is relatively intrinsically motivated, relatively internally controlled, free of many of the unnecessary constraints of objective reality . . . that is demarcated by clear cues, separating play from the rest of everyday life (i.e. framed clearly as play). (Bundy & Lane, 2020, p. 293)
The meaningfulness derives from the child’s perspective. What they are doing must be meaningful to them. If it is meaningful to them, they will intrinsically want to do it. Rather than structuring activities, consider allowing the child to choose what they want to do. It may involve use of the equipment, playing a board game, or creating imaginary scenarios with toy animals.
Praxis and regulation
The human body is a remarkable thing. The very inputs that facilitate improved praxis (tactile, vestibular and proprioception) also facilitate regulation. Besides vestibular sensory input going to the vestibular nuclei, ocular motor nuclei, cerebellum and the vestibular spinal pathways (Bundy & Lane, 2020), it also goes to an area of the brain called the insular cortex.
The insular cortex is the area of the brain that oversees physiological regulation and the autonomic nervous system (Gogolla, 2017). The same holds true for proprioception and tactile input. Tactile and proprioceptive sensory information goes to the somatosensory strip for sensory processing and motor planning. It also goes to the insular cortex.
Whether a child presents with SMD, SDD, or SMPD or any combination thereof, playing with them in a sensory gym, where they can bathe their nervous system in the enhanced vestibular, proprioceptive and tactile sensory input they receive from the equipment, is the balm their nervous systems need.