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Sensory integration is a theory which describes how the nervous system translates sensory information into action with the emphasis that behaviour is linked to neural processes. It refers to how the brain processes sensation and the resulting motor, behaviour, emotion and attention problems (Bundy, Lane & Murray, 2002) and is regarded as a frame of reference primarily by occupational therapists. Ayres (1972) theorised that impaired sensory integration may result in functional problems which she referred to as Sensory Integration Dysfunction. Ayres early research consistently found clusters of difficulties in children's motor skills, their behaviour, emotions and attention, these clusters have since been re validated in more recent research.
The term Sensory Integration is used outside of occupational therapy and can be applied to neurophysiological cellular processes rather than a behavioural response as proposed by Ayres. This overlap with terminology lead to a proposed Nosology (Miller, 2007) which supported the continued use of Sensory Integration Theory as defined above, Sensory Integration Treatment and evaluation process but proposed a new diagnostic categorisation for individuals who present with sensory integration challenges. This was to distinguish the disorder from the theory as well as the cellular processes (Miller et al, 2007). This continues to be one proposal for diagnostic terminology but requires further research to verify the clusters within it.
Research focusing on the characteristics of Sensory Integration Dysfunction (SID) has made progress in validating the tools used to measure this dysfunction/disorder. The diagnosis of SID is yet to appear in the ICD or the DSM, however it is referred to in the ‘Diagnostic Classification of Mental Health and Developmental Disorder of Infancy and Early Childhood’ (2005) as ‘Regulation Disorders of Sensory Processing’. Ongoing research continues to be conducted and developed to provide further evidence that this is a disorder in its own right. Evidence is emerging in the neuroscience literature linking behaviour and physiological measures in children such as cortisol levels, electro dermal activity (Schoen 2009, Lane 2009) and vagal tone (Schaaf, 2010). Brock et al (2012) found temperament dimensions distinguished children with ASD as a group but found these not to be associated with sensory response patterns, suggesting sensory integration difficulties as separate to ASD. Owen et al (2013) study has shown reduced white matter microstructural integrity, predominantly in the posterior cerebral tracts in children with atypical unimodal and multisensory integration behaviour. Studies such as this can help in distinguishing SPD from other over lapping conditions such as ASD/ADHD.
Research has supported the inclusion of sensory processing in the DSMV, clearly articulated as ‘minor’ diagnostic criteria for Autism, within domain 2, 'Repetitive, Restricted Behaviours'. The DSMV refers to ‘Hyper or Hypo reactivity to sensory input or unusual interest in sensory aspects of the environment’. The DSM acknowledges that these responses to sensation together limit and impair everyday functioning. In addition the NICE guidelines for the assessment, diagnosis and management/intervention for children, young people and for adults with ASD (2012) also recommend the assessment of hyper- and hypo-responsivity and adaptations of the physical environment for people with atypical sensoryresponses. The inclusion of sensory processing within both provides a rationale for assessment and intervention for this population. It is possible to identify hyper and hypo responsivity using the validated measures available such as the sensory profile and the SPM, in conjunction with occupation/functional assessment.
Until there is agreement reached regarding terminology and diagnostic criteria has been defined, it is essential that practitioners complete a comprehensive assessment to understand the sensory integration challenges/difficulties the individual is hypothesised to be experiencing. In order to interpret the results of measures such as the sensory profile or the sensory processing measure advanced knowledge of the neuroscience relating the how sensation is registered, discriminated, integrated and /or processed in order to make an adaptive response is required. Relying on a single assessment tool or measure may not provide the required clinical reasoning to inform intervention as SI therapy is hypothesised to be effective for people with SID/SPD.
When assessing an individual’s ability to process sensation it is useful to them and those close to them to define their challenges. Stating a sensory integration disorder can imply many challenges which are not applicable to them. However, stating that an individual is hyper responsive to certain sensations can be within their life context and can be linked to their occupational performance/participation challenges. This can be the same when using the clusters proposed by Ayres to link clusters of difficulties associated with bilateral integration and sequencing dyspraxia what the functional impairments are, the 'so what does this mean to the person in their daily life'.
Future diagnoses relating to sensory integration may be specific such as hyper responsivity, which is currently the most researched sensory processing difficulty/challenge. It may be that small gains are made and more specific diagnostics are confirmed as the research develops to support what is seen in clinical practice and reported by many individuals.