An fMRI Investigation of Audiovisual, Auditory and Visual Processing in Autism Spectrum Disorder

Background:  

The ability to integrate auditory and visual information is crucial to everyday life. Behavioural results have predominantly shown that individuals with Autism Spectrum Disorder (ASD) have deficits in audiovisual integration. These findings have recently been supported by electroencephalography (EEG) studies (Brandwein et al., 2015).

Objectives:  

There are limited data from functional magnetic resonance imaging (fMRI) studies investigating audiovisual processing in ASD. To address this issue and to reveal brain areas involved in audiovisual processing, the current fMRI study looked at audiovisual, unisensory auditory and unisensory visual processing in ASD.  Two types of stimuli were used, complex social face-voice (FV) displays and simple non-social beep-flash (BF) displays.

Methods:  

Participants included 13 adult males with ASD and age and 13 IQ-matched typically developed (TD) males. FV displays included an audiovisual condition of a face moving to say a single word and the voice saying the word, an auditory condition of a voice, and a visual condition a face moving to say a word. Similarly the BF displays included an audiovisual condition of a beep with a flashing circle, an auditory condition of a beep, and a visual condition of a flashing circle. The BOLD signal was obtained while participants were presented with blocks of audiovisual, auditory and visual conditions of FV and BF displays. 

Results:  

A random effects analysis contrasting groups revealed that processing of audiovisual as well as auditory and visual stimulus conditions in both the FV and BF displays was associated with reduced activation in ASD. Audiovisual, auditory and visual conditions of FV stimuli revealed reduced activation in ASD in regions of the frontal cortex, while BF stimuli revealed reduced activation in the lingual gyri. The inferior parietal gyrus revealed an interaction between sensory condition of BF displays and group.

A conjunction analysis was performed to show areas of audiovisual processing and revealed that the bilateral superior temporal cortex (STC) was sensitive to audiovisual information in ASD and TD for both types of displays. However, the activation regions of the STC were smaller in the ASD group. Additionally a superior frontal area was shown to be sensitive to audiovisual FV displays in the TD group, but not in the ASD group. 

Conclusions:  

Overall this study indicated differences in brain activity for audiovisual, auditory and visual processing of social FV and non-social BF displays in ASD compared to TD. These results were mainly characterized by the ASD group showing less activation than the TD group in auditory, visual and audiovisual regions.  In addition, differences were found in frontal cortex for FV displays.