Prefrontal Responses to Odors in Individuals With Autism Spectrum Disorders: Functional NIRS Measurement Combined With a Fragrance Pulse Ejection System

Abstract

Individuals with autism spectrum disorders (ASD) are impaired not only in social competencies but also in sensory perception, particularly olfaction. The olfactory ability of individuals with ASD has been examined in several psychophysical studies, but the results have been highly variable, which might be primarily due to methodological difficulties in the control of odor stimuli (e.g., the problem of lingering scents). In addition, the neural correlates of olfactory specificities in individuals with ASD remain largely unknown. To date, only one study has investigated this issue using functional magnetic resonance imaging (fMRI). The present study utilized a sophisticated method−a pulse ejection system−to present well-controlled odor stimuli to participants with ASD using an ASD-friendly application. With this advantageous system, we examined their odor detection, identification, and evaluation abilities and measured their brain activity evoked by odors using functional near-infrared spectroscopy (fNIRS). As the odor detection threshold (DT) of participants with ASD was highly variable, these participants were divided into two groups according to their DT: an ASD-Low DT group and an ASD-High DT group. Behavioral results showed that the ASD-High DT group had a significantly higher DT than the typically developing (control) group and the ASD-Low DT group, indicating their insensitivity to the tested odors. In addition, while there was no significant difference in the odor identification ability between groups, there was some discrepancy between the groups’ evaluations of odor pleasantness. The brain data identified, for the first time, that neural activity in the right dorsolateral prefrontal cortex (DLPFC) was significantly weaker in the ASD-High DT group than in the control group. Moreover, the strength of activity in the right DLPFC was negatively correlated with the DT. These findings suggest that participants with ASD have impairments in the higher-order function of olfactory processing, such as olfactory working memory and/or attention.

The amplitude of fNIRS hemodynamic response in the visual cortex unmasks autistic traits in typically developing children

“…Coherence analyses of resting-state hemodynamic activity showed weaker local and interhemispheric functional connectivity in different cortical regions [ 29 – 34 ]. Moreover, individuals on the autism spectrum present patterns of atypical activity, including reduced hemodynamic responses within specific brain regions, bilateral differences in neuronal activation, and the lack of cortical specialization, in tasks ranging from sensory perception [ 35 ] to executive functions [ 36 ], social perception [ 37 – 40 ], joint attention [ 41 – 43 ], imitation [ 44 , 45 ], facial and emotional processing [ 46 – 49 ], speech perception and language [ 50 – 53 ]. The majority of studies targeting evoked brain activity were focused on the prefrontal and the temporal cortex [ 28 ], where symptom severity seems to be inversely correlated with the degree of cortical activation [ 45 , 46 ].…”

Maternal microbes and early brain development in mouse

“…Furthermore, there is a directed increase in the volumes of the anterior olfactory nucleus (AON) and taenia tecta (TT) of the olfactory cortex (Figure 1B, 3B, and Supplementary Figure 1), which function as key areas for olfactory information processing and integration (61). Although relatively less explored, olfactory compromises are often observed in autism spectrum disorder patients (62,63) and correlated with the development of depression (64) and schizophrenia (65). The olfactory nerve undergoes a distinct developmental process (66), thought to involve the function of yet unknown odorant receptors (67), which may be directly responsive to gut microbiome-produced metabolites such as short-chain fatty acids and volatile amines that functions as odorants (68,69).…”

Hemodynamic Analysis for Olfactory Perceptual Degradation Assessment Using Generalized Type-2 Fuzzy Regression

“…Thus for each olfactory stimulus, a set of 10 days × 5 sessions/day × 5 trials/session = 250 trials are employed for each subject. The choice of 9S time interval, preceded by 3S stimulus presentation ensures sufficient elicitation of the neurons to obtain measurable response with appreciable resolution [32].…”