Linking Neuroscience,Function,and Intervention: A Scoping Review of Sensory Processing and Mental Illness

Auditory Processing.

Among the literature reviewed, studies in neuroscience have primarily explored aberrant sensory gating of auditory stimuli as measured by P50 event-related potentials and prepulse inhibition of the acoustic startle response. The P50 event-related potential is the brain’s electrophysiological response to a repeated stimulus that allows a person to habituate to that stimulus and remain vigilant for novel stimuli (Javitt & Freedman, 2015). Healthy people typically demonstrate an 80%–90% reduction in the amplitude of the P50 response to a redundant stimulus, whereas people with schizophrenia demonstrate only a 10%–20% reduction (Wan, Friedman, Boutros, & Crawford, 2008). Sensory gating enables a person to filter out irrelevant stimuli and focus on meaningful information in a stimulus-rich environment. Accordingly, deficits in sensory gating suggest an inability to filter out extraneous information. These findings have been replicated in people with first-episode psychosis who are antipsychotic-naive, thereby demonstrating that the deficit is a trait of the illness and not a result of pharmacological treatment (Hong et al., 2009). Although the majority of research in this area has focused on people with schizophrenia, studies have detected similar deficits in people with bipolar disorder and OCD (Cabranes, Ancín, Santos, Sánchez-Morla, García-Jiménez, Rodríguez-Moya, et al. 2013; Hashimoto et al., 2008). The functional implications of sensory gating deficits are significant; however, there is a gap in the literature exploring the impact of this deficit on occupational performance.

Another vein of research has confirmed deficits in MMN in adults with schizophrenia (Umbricht & Krljes, 2005). Mismatch negativity is a neural electrophysiological response that occurs when the brain recognizes an acoustic irregularity within a predictable pattern of stimuli. Atypical MMN increases the likelihood that people will miss information in sensory-rich environments (Javitt & Freedman, 2015). Studies have also shown that atypical MMN is related to deficits in affective prosody (Jahshan, Wynn, & Green, 2013), the ability to recognize emotion auditorily. Other studies have linked deficits in tone recognition to difficulties with emotion identification (Gold et al., 2012; Leitman et al., 2010). In people with bipolar disorder, basic auditory deficits have also been linked to impairments in emotion recognition (Zenisek et al., 2015). Navigating sensory-rich environments and identifying others’ emotions are important requisites for social participation; however, our review did not find research relating the aforementioned sensory deficits to participation in social occupations. Moreover, we did not find research studying clinical applications of this knowledge to occupational therapy interventions.

Visual Processing.

Research has demonstrated that adults with schizophrenia experience widespread disruption in neural activity at all stages of visual processing, from early sensory processing to higher order associations (Braus, Weber-Fahr, Tost, Ruf, & Henn, 2002; Jahshan et al., 2013). This population exhibits diminished neural responses to low-frequency visual targets (Martínez et al., 2012) and tends to have a dimmer perception of the world as a result of deficits in perceiving contrast (Kantrowitz, Butler, Schecter, Silipo, & Javitt, 2009). People with schizophrenia experience difficulty tracking slow-moving objects and exhibit rapid eye movement (i.e., saccades) as they repeatedly lose objects and attempt to catch up (Tien, Ross, Pearlson, & Strauss, 1996). Studies have also discovered that this population demonstrates atypical scanning patterns during free-viewing tests and deficits in maintaining a steady gaze on unmoving targets during fixation tasks (Benson et al., 2012).

Visual deficits are present in other mental illnesses as well. People with bipolar disorder experience disruptions at the latest stage of visual processing, which involves higher order functions of attention (Jahshan et al., 2013). In depression, visual and auditory sensory experiences frequently accompany depressive thoughts (Moritz et al., 2014), and visual attention is biased toward negative stimuli and away from positive stimuli (Victor et al., 2012). In adults with PTSD, studies have shown substantial cortical alterations in areas involved in visual object processing (Mueller-Pfeiffer et al., 2013). Despite the prevalence of visual deficits in mental illness, our review did not find any clinical applications of this research in the occupational therapy literature.

Other Sensory Deficits.

Fewer studies explored other forms of sensory dysfunction in mental illness. For instance, deficits in smell identification exist, particularly in schizophrenia; however, results are inconclusive regarding whether those deficits are trait markers of mental illness (Gill et al., 2014). Researchers have also found a potential link between proprioception deficits and disorders of self-awareness (Arnfred, Raballo, Morup, & Parnas, 2015). However, the scarcity of studies in these areas makes it difficult to draw broad conclusions regarding the prevalence of these deficits and their functional implications.

General Sensory Processing.

Our review found few occupational therapy studies that explored the impact of sensory processing deficits on occupational performance. Occupational therapists often embrace a holistic understanding of sensory processing and its impact on the lived experience instead of parsing out specific senses using a reductionist perspective. For instance, using the Adolescent/Adult Sensory Profile, Rieke and Anderson (2009) found that adults with OCD scored higher on low registration, sensory sensitivity, and sensation avoiding and lower on sensation seeking, but their study did not explore how these different processing patterns affect occupational performance. Brown, Cromwell, Filion, Dunn, and Tollefson (2002) found that people with schizophrenia have higher scores on sensation avoiding and low registration and lower scores on sensation seeking. Participants with bipolar disorder also scored significantly higher on sensation avoiding. Similar to findings from many neuroscientific studies on sensory gating, Brown et al. concluded that sensory deficits cause people to miss information and to avoid environments with particular sensory qualities. Similarly, Engel-Yeger et al. (2016) found that adults with major affective disorders were twice as likely to experience atypical sensory sensitivity, sensation avoiding, and low registration and 5 times more likely to experience lower sensation seeking than typical adults. We found no studies that explored clinical applications of these findings.

Impact of Basic Research.

Neuroscientists have made valuable contributions to understanding the most fundamental physiological processes of abnormal sensory function, and this knowledge has been useful in the development of pharmacological interventions. The occupational therapy research cited earlier is advantageous in understanding basic behavioral responses to sensory experiences (e.g., avoidance, seeking), but we discovered no research applying these findings to enhance understanding of occupational performance or to develop occupational therapy interventions. Researchers have suggested that deficits in sensory processing contribute to higher order cognitive deficits, such as difficulty concentrating or regulating oneself in environments that are rich with competing sensory stimuli (Wexler, Ikezawa, & Corbera, 2014). Accordingly, remedial interventions targeting sensory processing skills may contribute to cognitive gains and improved occupational performance. Support for remedial interventions that adopt a bottom-up approach to target sensory processing has increased (Jahshan et al., 2013; Moritz et al., 2014). Although this is a promising avenue for occupational therapy in mental health care, our review found no literature on the implications of sensory deficits in relation to real-world occupational performance.

Auditory Function.

Research has linked MMN deficits to lower scores on global function (i.e., Global Assessment of Functioning scale [American Psychiatric Association, 2002]) and level of independence in community living (Light & Braff, 2005). However, studies have not sufficiently explored how MMN affects occupational performance in sensory-rich environments in which various competing auditory stimuli must be modulated. Assessing the impact of MMN deficits on occupational performance is difficult because functional assessments are typically administered in sterile sensory environments that do not replicate the cacophony of real-world situations.

The ability to modulate competing stimuli and accurately identify a speaker’s tone is an integral aspect of social cognition (Green, Olivier, Crawley, Penn, & Silverstein, 2005), an essential skill for successful social participation. Accordingly, auditory deficits in emotion recognition have an impact on measures of social cognition (de Jong, de Gelder, & Hodiamont, 2013) and, presumably, on social functioning. For instance, early auditory deficits in schizophrenia have been linked to impairments in theory of mind and difficulty with perceiving sarcasm (Kantrowitz, Hoptman, Leitman, Silipo, & Javitt, 2014). Our review did not find research studying the link between deficits in tone recognition and participation in social occupations.

Visual Function.

Visual processing deficits have been associated with broad functional outcomes (Brittain, Ffytche, McKendrick, & Surguladze, 2010), but studies have not explored their impact on occupational performance. Research has found that adults with schizophrenia demonstrate functional single-word reading but experience significant deficits when reading paragraphs from real-world materials (Revheim et al., 2006). Kantrowitz et al. (2009) also suggested that this population experiences impairment in discerning nuanced information during complex task performance as a result of deficits in detecting visual contrast. The aforementioned deficits should be considered in designing interventions that use reading materials, but our review found no research on the implementation of such considerations in occupational therapy practice.

Sensory Modulation and Function.

In occupational therapy, few researchers have begun to study the impact of sensory deficits on the occupational participation of adults with mental illness. Lipskaya-Velikovsky, Bar-Shalita, and Bart (2015) found that adults with schizophrenia experience sensory modulation dysfunction, underresponsiveness, low satisfaction with activity performance, and low frequency of activity participation. However, their analyses did not find a significant correlation between sensory modulation and participation measures. Contrarily, Pfeiffer, Brusilovskiy, Bauer, and Salzer (2014) found a significant relationship between low levels of participation and high levels of low registration and sensory sensitivity on the Sensory Profile. Likewise, Good, Stanger, and McNulty (2012) suggested that participants’ (N = 5) high scores on low registration were associated with low motivation to cook, low scores on sensation seeking were associated with a lack of leisure activities, and high scores on sensation avoiding were associated with extended periods of staying in bed or avoiding treatment. Conflicting results and small sample sizes in this area expose a significant need for further occupational therapy research.

Social Participation.

The literature has revealed that adults with mental illness experience sensory deficits that potentially confound their ability to participate in meaningful social occupations. However, few studies have specifically targeted social functioning in relation to sensory processing. Engel-Yeger, Palgy-Levin, and Lev-Wiesel (2015) found that, in occupational therapy, sensory processing difficulties may impede adults with PTSD in forming intimate relationships. Stols, van Heerden, van Jaarsveld, and Nel (2013) found that atypical sensory processing patterns are related to how adults respond to anger situations or interpersonal conflict; high low registration was associated with aggression, and high sensation avoiding was associated with anger suppression. Further research is needed to untangle the potentially significant impact of sensory deficits on social occupational participation of adults with mental illness.

Sensory Rooms.

In occupational therapy, research has primarily supported the efficacy of deploying sensory rooms in inpatient psychiatric settings to reduce seclusion and restraint and manage aggression (Novak, Scanlan, McCaul, MacDonald, & Clarke, 2012; Sutton, Wilson, Van Kessel, & Vanderpyl, 2013). However, these are pilot studies with small sample sizes, which limits their generalizability. An increasing number of studies have postulated the efficacy of sensory rooms, but randomized controlled trials are needed to strengthen the evidence base. Despite the absence of definitive rigorous evidence, there is growing consensus regarding the importance of harnessing the sensory environment to support patients’ occupational engagement and to mitigate the occurrence of negative mental states (Champagne & Stromberg, 2004).

Sensory Integration and Sensory Modulation.

A limited number of studies explored the use of sensory integration (SI) treatment with adults with mental illness. Blakeney, Strickland, and Wilkinson (1983) studied the effects of a 6-wk SI program with 14 adults with schizophrenia but found no statistically significant improvements in outcome measures. Contrarily, Kaiser, Gillette, and Spinazzola (2010) found that SI treatment with patients with PTSD generated significant improvement. In addition, Moore and Henry (2002) found that the Wilbarger protocol had a positive impact on sensory defensiveness for three women with a history of self-injurious behavior. The scarcity of studies in this area prevents reliable conclusions regarding the efficacy of SI for adults with mental illness.

Sensory modulation programs, which promote sensory awareness and client centeredness, are increasingly used by occupational therapists in psychiatry. In a pilot study, Gardner (2016) implemented a program that introduced patients to the concept of sensory modulation and provided specific sensory strategies to address levels of arousal. Participants reported decreased arousal when using the learned sensory strategies and identified the treatment as valuable to their recovery. Similarly, Champagne (2011) found that a sensory modulation program generated positive improvement in occupational engagement and work performance in a single case study. However, among the few studies that tested the efficacy of sensory modulation programs, insufficient information was provided regarding the intervention protocol to facilitate replication of the studies or to guide therapists in implementing the programs. More research is needed to test sensory modulation programs and to apply current understandings of sensory deficits in neuroscience to occupational therapy.