Differences in auditory latency (the time between the input is received and when reaction is observed in the brain), hypersensitivity to vibration in the Pacinian corpuscles receptor pathways and other alterations in unimodal and multisensory processing have been detected in autism populations.People with sensory processing deficits appear to have less sensory gating than typical subjects, and atypical neural integration of sensory input. In people with sensory over-responsivity, different neural generators activate, causing the automatic association of causally related sensory inputs that occurs at this early sensory-perceptual stage to not function properly. People with sensory over-responsivity might have increased D2 receptor in the striatum, related to aversion to tactile stimuli and reduced habituation. In animal models, prenatal stress significantly increased tactile avoidance.Recent research has also found an abnormal white matter microstructure in children with SPD, compared with typical children and those with other developmental disorders such as autism and ADHD.One hypothesis is that multisensory stimulation may activate a higher-level system in the frontal cortex that involves attention and cognitive processing, rather than the automatic integration of multisensory stimuli observed in typically developing adults in the auditory cortex. Diagnosis
Sensory processing disorder is accepted in the Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood (DC:0-3R). It is not recognized as a mental disorder in medical manuals such as the ICD-10 or the DSM-5.Diagnosis is  primarily arrived at by the use of standardized tests, standardized questionnaires, expert observational scales, and free-play observation at an occupational therapy gym.
The AAP has plans to review its policy, though those efforts are still in the early stages.A 2015 review of research on Sensory Integration Therapy (SIT) concluded that SIT is "ineffective and that its theoretical underpinnings and assessment practices are unvalidated", that SIT techniques exist "outside the bounds of established evidence-based practice", and that SIT is "quite possibly a misuse of limited resources".Some sources point that sensory issues are an important concern, but not a diagnosis in themselves.Critics have noted that what proponents claim are symptoms of SPD are both broad and, in some cases, represent very common, and not necessarily abnormal or atypical, childhood characteristics. Where these traits become grounds for a diagnosis is generally in combination with other more specific symptoms or when the child gets old enough to explain that the reasons behind their behavior are specifically sensory. Manuals
SPD is in Stanley Greenspans Diagnostic Manual for Infancy and Early Childhood and as Regulation Disorders of Sensory Processing part of The Zero to Threes Diagnostic Classification. Is not recognized as a stand-alone diagnosis in the manuals ICD-10 or in the recently updated DSM-5, but unusual reactivity to sensory input or unusual interest in sensory aspects is included as a possible but not necessary criterion for the diagnosis of autism. History
Sensory processing disorder as a specific form of atypical functioning was first described by occupational therapist Anna Jean Ayres (1920–1989).