Olfaction and taste processing in autism

Abstract

Background: Autism is often associated with sensory symptoms, but few studies have examined chemosensory functions in this population. We examined olfactory and taste functioning in individuals with autism to characterize chemosensory processing and test competing hypotheses about underlying brainstem versus cortical abnormalities.

Methods: Twenty-one participants (10-18 years) with autism were compared with 27 well-matched control participants with typical development. Taste identification was tested via sucrose, NaCl, citric acid, and quinine solutions applied to standard locations on the anterior tongue. Taste detection thresholds were established in the same regions with electrogustometry, and olfactory identification was evaluated with "Sniffin' Sticks."

Results: Participants with autism were significantly less accurate than control participants in identifying sour tastes and marginally less accurate for bitter tastes, but they were not different in identifying sweet and salty stimuli. Taste detection thresholds via electrogustometry were equivalent. Olfactory identification was significantly worse among participants with autism.

Conclusions: True differences exist in taste and olfactory identification in autism. Impairment in taste identification with normal detection thresholds suggests cortical, rather than brainstem dysfunction. Further research is needed to determine the neurologic bases of olfactory and taste impairments, as well as the relationship of chemosensory dysfunction to other characteristics of autism.

Figure 1. Taste Identification Accuracy

Group means for percent accuracy on individual tastants, collapsed across side of presentation. Error bars represent standard error of the mean. * p < .05, † p < .10

Figure 2. Electrogustometry Detection Thresholds

Boxplots show each group's full range of threshold detection points for the anterior tongue (chorda tympani region), collapsed across side of presentation. Boxes represent the interquartile ranges, whiskers are the 10^th and 90^th percentiles, and open circles are scores beyond these points. Group means are indicated by a dashed line, and medians by a solid line. Output current for thresholds is reported in decibels (possible range was −6 to 34 dB).

Figure 3. Olfactory Identification

Group means for percent accuracy on “Sniffin' Sticks” Odor Identification Test. Error bars represent standard error of the mean. ** p < .01