Sensory processing involves the reception of and automatic neurobiological responding to stimuli from the outside environment (Brown, Tollefson, Dunn, Cromwell & Fillion, 2001). The proposition that we learn through our senses has been widely accepted within the fields of mental health and child development for over half a century. For example, Piaget (1958) described how the infants’ coordination of sensorimotor actions forms the foundation of cognitive development as they become internalized, and symbolically represented in memory.
With the advent of more sophisticated technologies in neuroscience, the various ways that sensory stimuli are processed in the brain were elucidated in the late 1970’s-1980’s (LeDoux, personal communication, 2016). Joseph E. LeDoux, for example was one of the early pioneers of affective neuroscience, and demonstrated in rodent models that sensory stimuli is the forerunner to emotional responding (Almada, Periera Jr. & Carrara-Augustonborg, 2013). In 1990, LeDoux made this connection overtly clear in the title of his paper “Information flow from sensation to emotion: Plasticity in the neural computation of stimulus value.”
The senses, then, are connected to complex and incalculable neural processes, including perception, learning, memory, motor coordination and emotion regulation (Brown et al., 2001; Kandel, Schwartz, & Jessell, 2000; Shepherd, 1994). In addition, over the past 20 years, sensory processing problems related to the tactile, auditory, visual, gustatory, olfactory, proprioceptive, and vestibular systems have been associated with various problems related to daily living. These problems include motor planning, visual and auditory discrimination as well as the processing and reacting to sensory stimuli in a graded manner (Bundy & Murray, 2002; Greenspan & Porges, 1984; Kandel et al., 2000; Reeves, 2001; Schaaf & Anzalone, 2001; Wiener, Long, DeGangi, & Battaile, 1996; Williamson & Anzalone, 2001). Early estimates of the prevalence of sensory processing problems in Kindergarten children were 5% (Ahn, Miller, Milberger, & McIntosh, 2004). In contrast, estimates of atypical sensory processing in children with developmental disabilities were between 40-88% (Adrien et al., 1993; Dahlgren & Gillberg, 1989; Kientz & Dunn, 1997; Ornitz, Guthrie, & Farley, 1977; Talay-Ongan & Wood, 2000).
Sensory Over Responsivity (SPD-SOR)
The inability to respond to sensory stimuli in a graded manner refers to individuals who may over-respond, under-respond or crave more sensory stimulation than others. Sensory Over Responsivity, or SOR, describes children who react adversely to sensory stimuli that others find neutral or even pleasant. (Ahn, et al., 2004). Prevalence estimates of children who are over responsive to sensory stimuli (SPD-SOR) are estimated to be 16% in children 7-11 years old (Ben-Sasson, Carter & Briggs-Gowan, 2009).
In a ground breaking study McIntosh, Miller, Shyu, & Hagerman (1999) used electrodermal activity and vagal tone as dependent measures. The researchers found that children with SPD-SOR demonstrated a greater sympathetic response (i.e., freeze, fight or flight response) to stimuli, as well as a weaker parasympathetic response (i.e., the system referred to as “rest and digest”; McCorry, 2007). SPD-SOR children demonstrated responses to stimuli that were larger in amplitude, more frequent, and/or of longer duration compared to typical peers. In addition, they demonstrated specific difficulties in habituation, manifesting difficulties returning to baseline arousal compared to typical peers (McIntosh et al., 1999; Schaff & Anzalone, 2001). Notably, later research comparing sensory over responsive children with Autistic Spectrum Disorder (ASD) children revealed that while ASD children were more likely to under-respond to sensory stimuli than children with SPD, over-reactivity within both groups were similar. (Tavassoli et al., 2017). Finally, a more recent neuroimaging study revealed strong evidence for specific brain differences in children with SPD, adding more validity to the diagnosis. In this study boys with SPD were found to have decreased white matter connectivity, particularly in the parietal regions of the brain (Owen et al., 2013).
SOR, Auditory Gating and Misophonia
Research supports a decreased ability to auditory gate in children with SPD. In other words, children with SPD are less able to detect changes in the frequency and the loudness of auditory tones presented sequentially (compared to typically developing control children; Davies et al., 2009, 2010; Davies & Gavin, 2007; Gavin et al., 2011). It is interesting to note that parallel to this research Jastreboff and Jastreboff (2001) termed the newly proposed disorder Misophonia.
Misophonia is a newly termed disorder (Jastreboff & Jastreboff, 2001) that shares a phenotype similar to auditory over-responsivity (SOR specific to the auditory sense) and is particularly relevant to auditory gating. Although the research on this disorder is in its infancy, Misophonia is considered a neurophysiological condition characterized by heightened physiological responsivity and a high level of emotional reactivity resulting from intolerance to specific auditory, and sometimes visual, stimuli (Jastreboff & Jastreboff, 2001; Jastreboff & Jastreboff, 2014; Moller, 2011; Edelstein, et al., 2013). Originally described by Jastreboff and Jastreboff (2001), individuals with Misophonia demonstrate increased sympathetic nervous system arousal, accompanied by emotional distress in response to specific pattern-based sounds, irrespective of decibel level (Kumar et al., 2017; Schröder, Vulink & Denys, 2013). Examples of these sounds include other people chewing, throat clearing, slurping, finger tapping, foot shuffling, keyboard tapping, and pen clicking (Edelstein et al., 2013; Rouw & Erfanian, 2017). Additionally, some sufferers have reported experiencing visual triggers, such as leg-shaking, mouth movements, chest movements, etc. (Edelstein et al., 2013; Schröder et al., 2013). Preliminary experimental studies have noted hyper-myelination between the parts of the brain that process auditory stimuli and parts of the brain that process emotion (as well as detecting salience of stimuli; Kumar et al., 2017).
To date there have been no studies directly comparing Misophonia with SOR. Nor have there been studies exploring whether earlier and more generalized auditory over responsivity is a risk factor for the specific sounds in Misophonia. However, because of the overlaps between Misophonia and SOR, exploration of how self-regulatory skills develop in Misophonia is warranted as part of a larger discussion of SOR, and self-regulation.