An MEG Study of High-Frequency Brain Oscillations in Autism and First-Degree Relatives During Picture Naming

Background:  

Fusiform gyrus (FG) hypoactivity has been reported in individuals with Autism Spectrum Disorders (ASD), and it is still unknown whether this is an inheritable abnormality. Because of the importance of face processing to successful social functioning, the FG has been extensively studied as being a part of the visual system specialized in facial recognition, also called Fusiform Face Area. However, other functions have been attributed to the FG, such as its role in language processing (e.g., the visual word form area). High-frequencies brain activities, such as gamma oscillations, have been demonstrated to be abnormal in the visual and auditory cortices of people with ASD. We have also established that these deficits are seen in adult first-degree relatives, suggesting that such impairment constitutes an autism endophenotype.

Objectives:  

To compare high-frequency gamma brain oscillations in the FG of control participants to patients with autism and first-degree relative of persons with ASD during a picture naming task.

Methods:  

Participants were 12 persons with ASD, 16 parents of an autism child and 35 controls. Whole-head MEG recordings were acquired during a picture naming task, in which subjects were asked to subvocalize names of objects presented on a screen. Virtual sensors were created in the fusiform gyrus from source analyses of the MEG data (SPM8) and oscillatory activity between 5 and 120 Hz was analyzed across a 1 second window using wavelet-based time-frequency methods. Measures of evoked power and phase-locking factor (PLF) were derived for each subject. Mass univariate, non-parametric statistical analyses were performed across the entire time-frequency space and corrected for multiple comparisons using cluster size metrics, p < .05.

Results:  

Whereas there was no significant difference among groups within the low-gamma (40Hz) oscillations (or any frequency below ~60-70 Hz), PLF showed significant reduction at high-gamma frequencies (around 80Hz) between 160 and 600 msec after stimulus presentation in both the parent and autism groups, relative to control subjects.

Conclusions:  

These findings support the known impaired activation of the FG in autism but also suggests that the high gamma-band range may be important for higher cognitive functions that are mediated by FG activation. The presence of the finding in parents suggests that the previously described gamma-band ASD endophenotype may be relevant to higher order visual object processing and possibly to aspects of language function.