Reduced Transient and Steady-State Auditory Gamma-Band Activity in Children with Autism Spectrum Disorders and Their Unaffected Siblings

Background: Current diagnoses of autism spectrum disorders (ASD) are based entirely on behavioral observation and caregiver interviews, so the discovery of physiological markers of ASD would provide objective markers of the condition, facilitating further research and treatment. Synchronous neural activity in the gamma range (30-80 Hz) has been shown to be abnormal in individuals with ASD and could be a potential biological marker of ASD.  Reduced auditory evoked gamma-band activity and/or reduced gamma-band phase locking factor (PLF) have been found in both children and adults with ASD in response to pure and amplitude-modulated tones.  This has also been found in unaffected parents of children with ASD, suggesting potential familiality of these abnormalities.  This has not previously been investigated in unaffected siblings of children with ASD. 

Objectives: The goal of the current study was to assess transient and steady-state auditory gamma-band responses in children with ASD and their unaffected siblings to determine if gamma-band abnormalities are familial.  This would extend previous research finding gamma-band abnormalities in both individuals with ASD and their unaffected parents.  If gamma-band abnormalities are familial, both children with ASD and their unaffected siblings would be expected to exhibit these abnormalities.  

Methods: Magnetoencephalography (MEG) recordings were obtained for a group of children with ASD (N=13), their unaffected siblings (N=16) and a group of healthy control children (N=18).  Evoked gamma-band power and gamma-band PLF in response to 40 Hz amplitude-modulated sounds were measured for transient and steady-state responses.    

Results: The ASD group demonstrated significantly reduced steady-state right hemisphere auditory evoked gamma-band power compared to the control group, p < .05 (cluster-wise correction for multiple comparisons).  There was also a trend toward both the ASD and sibling groups showing reduced transient and steady-state auditory evoked gamma-band power in left hemisphere compared to the control group (uncorrected p < .05).  In addition, both the ASD and sibling groups demonstrated a trend toward reduced PLF in both right and left auditory cortex compared to controls (uncorrected p < .05).  

Conclusions: Children with ASD and their unaffected siblings both showed reduced evoked gamma-band responses and gamma-band PLF compared to controls, which is consistent with previous findings in individuals with ASD and their unaffected parents. These results suggest that the gamma-band abnormalities seen in those with ASD are familial, and that gamma-band activity is a potential biological marker of ASD.