Sensory Modulation Disorder (SMD), a sub-set of the larger category Sensory Processing Disorder (which was called Sensory Integration Disorder), is at the top of the learning curve today given recent conversations with Kara's kingergarten teachers. Both of them describe a child unable to focus her mind or body, a condition that used to only be challenging for the teacher but increasingly results in alienation from her peers.
Research into SMD builds on two foundations. First are the core writings of Dr. A. Jean Ayres. Beginning with Tactile Fuctions (1964) and Sensory Integration and the Child (1972) and most recently in her 1989 "Sensory Integration and Praxis Test," Ayre's description of sensory integration provided the field's inceptive principles. The second foundation is neuroscience. The concepts supporting sensory modulation have evolved in accordance with new insights into the brain. The last 30 years have seen many new insights which must be incorporated into any theory of brain-behavior relationships. Most prominent: the notion of a hierarchically organized brain has been replaced by a heterarchical, parallel, distributed processing model of brain structure and function. Theoretical models derived from less complex brain system representations do not offer a current conceptualization of what has been discovered about brain functioning. This coupled with the brains’ amazing ability to develop based on experience, whether that be initial development, or reorganization following damage, provides increasing interest in OT theory and intervention. These changes in neuroscience require an updating of our theories to incorporate the new findings in order to facilitate acceptance of our unique perspective on central nervous system functioning as it relates to human occupation. Taken together, SMD has emerged as a hot-topic in the psychological sub-set of Occupational Therapy (OT). The 1998 AOTA Annual Conference in Baltimore, MD, devoted an entire day to it. Definitions are still being written and clarified; debate is still being carried on around treatment and its location on various therapeutic continuii.
So what is "sensory modulation"? Parham and Mailloux (1996) define sensory modulation as "a tendency to generate responses that are appropriately graded in relation to incoming sensory stimuli rather than under reacting or overreacting to them." They support the views expressed by Cermak (1988) and Royeen (1989) that modulation disorders (though the reference is more to disruption than disorder) are represented by a continuum from registration problems to sensory defensiveness. They describe dysfunction as either fluctuations or a tendency to function at one extreme or the other. They further describe sensory registration problems as a failure to attend to or register relevant environmental stimuli. They describe a situation where lack of registration creates a lack of inner drive to engage in typical childhood occupations and is detrimental to long term development. Tracy Stackhouse of the University of Denver offers another definition of sensory modulation. "Sensory modulation is the intake of sensation via typical sensory processing mechanisms such that the degree, intensity and quality of response is graded to match environmental demand and so that a range of optimal performance/adaptation is maintained." As an addition, it is worth recalling that "fun" is the child's word for sensory integration. If there are integratory issues, we would expect them to appear most obviously in the experience and expression of play, social or otherwise.
The big three behavioral signs for SMD are all there: avoidance, distractibility and increased activity level. Occupational therapists Koomer and Bundy (1991) state, ""when an individual overresponds, underresponds or fluctuates in response to sensory input in a manner disproportional to that input, we say that the individual has a sensory modulation disorder" (p. 268, 1991). They also describe a complex condition, which paradoxical to a continuum model, allows for an individual to have problems with both discrimination and modulation of sensation. Kimball agrees, describing sensory modulation problems in terms of the arousal state created due to the influences of sensation. "Persons who have sensory system modulation problems have more changeable arousal or reaction levels than normal. This results in problems with adaptive responses because there systems lack stability" (p 96-97). Kimball related these behavioral phenomenon to the classic inverted U shaped curve (Hebb, 1949), highlighting an important concept that "sensory system modulation fluctuates within a range of normal,"(p. 98). In this conceptualization, performance and adaptive capacity are poor at both low and high level of arousal. In the middle ranges of arousal, performance and adaptation are optimal. Additionally, Kimball reiterated the notion that a single sensory system may not be isolable, "sensory systems do not function independently. Arousal in several systems can combine" (p. 97, 1993). Or simply consider this sentence from the Wikipedia article on Sensory Integration Dysfunction: "An example of a child with hyposensitivity is one who constantly gets up and down in a classroom and is constantly seeking sensory stimulation."
Research into SMD is going on constantly. The work of Grace Baranek suggests sensory defensiveness as a unifying construct, with smaller sub-sets of modality specific disruptions, such as auditory sensitivity. Winnie Dunn and her colleagues have been developing a normed parent questionnaire, the Sensory Profile (Dunn & Westman, 1997). An analysis of the responses made by parents of typical children on the 125 items revealed nine factors related to sensory integration some of which reflect sensory modulation and reactiveness (Dunn & Brown, 1997). These factors include sensory seeking, emotional reactivity, low endurance/tone, oral sensitivity, inattention/distractibility, poor registration, sensory sensitivity, sedentary, and fine motor/perceptual. Dunn further has suggested that sensory modulation needs to be considered on the multiple dimension of a person’s threshold for sensory events and responsiveness to sensation (Dunn, 1997).
And finally, having said all of that, one should be aware of a significant behavioral overlap between SMD, behavioral problems, physiological problems (the kid can't hear well), or anxiety. To quote the wikipedia article, "while this diagnosis is accepted widely among occupational therapists and also educators, these professionals have been criticized for overextending an already-poorly-supported model that attempts to explain emotional and behavioral problems that are better (and more simply) explained in other ways."
Some Relevant Websites
Occupational Therapy Innovations Sensorimotor Page
The SPD Network
Signs, Symptoms and Background Information on Sensory Integration
Asynchronous development and sensory integration intervention in the gifted and talented population Some very good and practical information.
Sensory Integration International
Cermak, S. (1988). the relationship between attention and sensory Integration Disfunction (Part 1), Sens Integration Special Interest Section Newsletter, 11, 1-4. (Published by AOTA, Bethesda, MD)
Dunn, W., & Westman, K. (1997). The Sensory Profile: The Performance of a National Sample of Children without Disabilities. American Journal of Occupational Therapy, 51(l), 25-34.
Dunn, W., & Brown, C, (1997). Factor analysis on the Sensory Profile from a national sample of children without disabilities. American Journal of Occupational Therapy, 51, 490-495.
Dunn, W. (1997). The impact of sensory processing abilities on the daily lives of young children and their families: A conceptual model. Infants and Young Children, 9 (4), 23-35.
Dunn, W., & Fisher, A. (1983). Sensory registration, autism and tactile defensiveness. Sensory Integration Special Interest Section Newsletter, 6 (2), 3-4. (Published by AOTA, Bethesda, MD)
Parham, L. D., & Maillous, Z. (1996). Sensory Integration and Children with Learning Disabilities. In P. N. P. Allen eds. Occupational Therapy in Children (pp. 307-355). St. Louis: Mosby.
Royeen, C. (1989). Commentary of "Tactile functions in learning disabled and normal children: Reliability and validity considerations". Occupational Therapy Journal of Research, 9, 16-23.
One should note that this post copies egregious sections of the article: Julia Wilbarger and Tracy Murnan Stackhouse "Sensory Modulation: A Review of the Literature" http://www.ot-innovations.com/sensory_modulation.html [Accessed April 11, 2006.].