Autism spectrum disorders and chemoreception: dead-end or fruitful avenue of inquiry?

Autism Spectrum Conditions (including Autism Spectrum Disorder/ASD, Asperger’s Syndrome/AS, and pervasive developmental disorder/PDD) are neurodevelopmental disorders characterized by clinical impairments in social interaction and communication, and stereotypical and repetitive patterns of behavior (DSM-IV-TR, 2000; ICD-10, 1993). Since the term first gained currency through the pioneering work of Kanner in 1943 who described 11 cases of “autistic disturbance of affective contact and... desire for preservation of sameness”, it has subsequently been incorporated into DSM in 1999 and has been further re-defined in DSM-V to now describe one category of disorder (Autism Spectrum Disorder) with two dimensions: social communication impairment and repetitive behavior [see Kent et al. (2013), for commentary]. This paper considers the literature concerning one of the least studied aspects of ASD: chemosensory perception, and evaluates critically some of the current methods and practices in this area. To our knowledge, this is the first systematic review of this field. Current evidence suggests that, in addition to the stereotypical characteristics of ASD, impairments are found in some cognitive, perceptual and sensory domains but not others. At the perceptual level, the most commonly studied function is face processing, and the recognition of emotion in faces -both types of processing are thought to be impaired (Klin et al., 1992; Spezio et al., 2007); although see Klin (2008). In other sensory/perceptual domains, ASD has been associated with problems in processing dynamic noise, motion detection (Marco et al., 2011), processing pitch loudness and complexity especially if the auditory stimulus is speech (O’Connor, 2012)and, if individuals are high functioning, free-recall frommemory (although recognitionmemory is relatively intact). A moderate impairment in recognition and severe impairment in free recall is found in low-to-medium functioning individuals with autism (Boucher et al., 2012). While the focus of behavioral work has been cognitive and perceptual, specifically auditory and visual, it is striking that few studies have examined sensory processes such as gustation and olfaction (Martin, 2013). To date, there have been two empirical studies of taste in ASD/AS (Bennetto et al., 2007; Tavassoli and Baron-Cohen, 2012a) and nine empirical studies examining olfactory function, principally olfactory identification, discrimination and detection ability, and participants’ hedonic response to odor (chronologically: Suzuki et al., 2003; Bennetto et al., 2007; Brewer et al., 2008; Dudova et al., 2011; Hrdlicka et al., 2011; May et al., 2011; Legisa et al., 2012; Tavassoli and Baron-Cohen, 2012b; Galle et al., 2013). Empirical studies have been motivated partly by questionnaire and selfreport studies of sensory behavior and food consumption. ASD individuals have been reported to exhibit highly irregular or abnormal responses to tastes, smells and foods [see, e.g., (Kientz and Dunn, 1996; Brown et al., 2001; Schreck and Williams, 2005)]. These empirical studies have sought to examine whether such behaviors can be recorded more systematically and experimentally. The most commonly studied olfactory function is identification (Six studies: Suzuki et al., 2003; Bennetto et al., 2007; Brewer et al., 2008; Dudova et al., 2011; May et al., 2011; Galle et al., 2013) with four studies investigating detection (Suzuki et al., 2003; Dudova et al., 2011; Tavassoli and Baron-Cohen, 2012b; Galle et al., 2013) and one, discrimination (Galle et al., 2013). The majority of studies has examined olfactory function in children and adolescents (Bennetto et al., 2007; Brewer et al., 2008; Dudova et al., 2011; Hrdlicka et al., 2011; May et al., 2011; Legisa et al., 2012); three studies have examined adults’ responses (Suzuki et al., 2003; Tavassoli and Baron-Cohen, 2012b; Galle et al., 2013). All studies recruit high-functioning (HFA) participants. The control groups in these studies comprise typically developing, ageand IQ-matched participants. Four studies are exclusively single-sex-based with two studying men only (Suzuki et al., 2003; Galle et al., 2013), two studying boys only (Dudova et al., 2011; Hrdlicka et al., 2011) and one recruiting primarily boys (May et al., 2011). Identification, detection and discrimination are considered the olfactory functional triad as these are the abilities essential to the perception of scent. Identification is conventionally measured via the University of Pennsylvania Smell Identification Test (UPSIT) or Sniffin’ Sticks and it is a positive aspect of ASD studies that they administer these wellvalidated measures. The former involves