Elsevier

Biological Psychiatry

Volume 62, Issue 3, 1 August 2007, Pages 192-197
Biological Psychiatry

Original Article
Children and Adolescents with Autism Exhibit Reduced MEG Steady-State Gamma Responses

https://doi.org/10.1016/j.biopsych.2006.07.002Get rights and content

Background

Recent neuroimaging studies of autism have indicated reduced functional connectivity during both cognitive tasks and rest. These data suggest long-range connectivity may be compromised in this disorder, and current neurological theories of autism contend disrupted inter-regional interactions may be an underlying mechanism explaining behavioral symptomatology. However, it is unclear whether deficient neuronal communication is attributable to fewer long-range tracts or more of a local deficit in neural circuitry. This study examines the integrity of local circuitry by focusing on gamma band activity in auditory cortices of children and adolescents with autism.

Methods

Ten children and adolescents with autism and 10 matched controls participated. Both groups listened to 500 ms duration monaural click trains with a 25 ms inter-click interval, as magnetoencephalography was acquired from the contralateral hemisphere. To estimate 40 Hz spectral power density, we performed time-frequency decomposition of the single-trial magnetic steady-state response data using complex demodulation.

Results

Children and adolescents with autism exhibited significantly reduced left hemispheric 40 Hz power from 200-500 ms post-stimulus onset. In contrast, no significant between group differences were observed for right hemispheric cortices.

Conclusions

The production and/or maintenance of left hemispheric gamma oscillations appeared abnormal in participants with autism. We interpret these data as indicating that in autism, particular brain regions may be unable to generate the high-frequency activity likely necessary for binding and other forms of inter-regional interactions. These findings augment connectivity theories of autism with novel evidence that aberrations in local circuitry could underlie putative deficiencies in long-range neural communication.

Section snippets

Subject Selection

Ten participants with autism (ages 7–17) and 10 controls (ages 8–16) participated in this experiment. All participants with autism met clinical criteria for DSM-IV autistic disorder (American Psychiatric Association 1994), as well as criteria for autism on the Autism Diagnostic Interview–Revised (ADI-R; Lord et al. 1994) and Autism Diagnostic Observation Schedule-Generic (ADOS-G; Lord et al. 2000) as assessed by a researcher trained to research criteria. Two subjects from each group were

Demographic Variables

Our groups did not significantly differ on age (p > .75), handedness (p > .80), or education (p > .60). However, as shown in Table 1, autistic participants exhibited significantly lower scores on all IQ measures. To examine whether IQ was related to 40 Hz power, we computed Pearson-correlation coefficients using each IQ scale (verbal, performance, full) and relative 40 Hz mean power for each hemisphere (i.e., 6 total correlations). Our results showed no evidence of correlation between IQ and 40

Discussion

We examined gamma band power of auditory SSR in a group of healthy children and adolescents, and an age-matched sample with autism. Our results indicated right hemispheric gamma power increases were relatively equal between control and autistic participants. Conversely, gamma power fluctuations for left hemispheric cortices showed significant disruption in participants with autism, as the series of pulse trains did not elicit a SSR of increased 40 Hz power (relative to baseline) as it clearly

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