Praxis-Related Alterations of Cortical Oscillations in Children with Autism: Associations with Symptom Severity, Repetitive Behaviors and Motor Planning

Background: The ability to perform praxis gestures--learned, skilled movements--has been linked both theoretically and empirically with the cardinal features of autism spectrum disorders (ASD). Because the praxis network is well characterized, and because motor behaviors are relatively easy to quantify and manipulate, praxis function serves as an excellent model system in ASD. To explore frontal-parietal network function in ASD, subjects performed a praxis task during EEG recording.

Objectives: To assess the specificity of task-related oscillatory differences in ASD as well as their relationship to key behavioral measures.

Methods: 20 children with ASD and 28 controls (typically developing; TD) ages 8-12 years performed a praxis preparation and execution task while EEG was recorded. We assessed broad-band event-related spectral perturbations (ERSP; task-related change in signal power). We specifically examined the premotor (central) and parietal regions known to be related to praxis function. Behavioral assessment included the Autism Diagnostic Observation Schedule (ADOS), the Autism Diagnostic Interview (ADI) and the Postural Knowledge Test (PKT; a “perceptual” test of praxis ability).

Results: Event-related synchronization (ERS; task-related increases in signal power) were seen in the theta band (2-8 Hz), and event-related desynchronization (ERD; task-related decreases in power) were seen in alpha (7-13 Hz) and beta (18-22 Hz) bands in both groups. The groups differed specifically in magnitude of beta ERD in left central channels as well as alpha ERD in left posterior channels. Further, the degree of posterior alpha ERD attenuation was associated with increased autism severity overall as well as impaired performance on a perceptual “praxis” task in the ASD group. The degree of attenuation of central beta ERD was correlated with restricted/repetitive behaviors and interest on both the ADOS and ADI.

Conclusions:   Consistent with predictions, the ASD patients had an attenuation of task-related EEG oscillatory responses. The nature of these group differences, however, was quite specific: differences were only seen on the left, consistent with the known lateralization of the praxis network. Deficits in central beta suppression (ERD) in ASD were associated with degree of restricted/repetitive behavior; this may be due to the putative role of central beta as a mediator of “status quo” activity. Deficits of posterior alpha suppression were associated with impairment of “perceptual” or posterior aspects of praxis function as well as overall ASD symptom severity, thus adding to the evidence supporting the role of frontal-parietal networks in motor as well as social/communicative aspects of the autistic phenotype. Further, deficits in oscillatory activity may implicate inhibitory interneurons, whose function is thought to be altered in ASD. The results provide specific evidence that impaired modulation of oscillatory activity may have a direct effect upon autistic symptoms.