Pivotal Response Treatment Increases Processing Efficiency for Social Information

Background: The social motivation hypothesis of autism proposes that people with autism spectrum disorders (ASD) experience reduced reward for social stimuli, resulting in decreased attention to people, and consequent dysfunction in the developmental specialization of neural mechanisms associated with social behavior. Pivotal response treatment (PRT) is an empirically validated behavioral treatment for ASD that directly targets social motivation to address deficits in interpersonal interaction and communication. Prior work from our group has indicated that a 4-month course of PRT results in measurable changes in pragmatic language, social engagement, and adaptive functioning, with accompanying changes in regional brain activation (Voos et al., 2012). Treatment outcome in terms of neural efficiency has not yet been studied.  The current study applies EEG, an imaging method with excellent temporal resolution, to examine the temporal dynamics of the neural mechanisms associated with positive response to intervention.

Objectives: To identify temporal changes in neural mechanisms associated with social perception subsequent to PRT treatment and their association with behavioral outcome measures.

Methods: Five children with ASD between 4 and 6 years of age received PRT for 8 hours per week (6 hours with the child and 2 hours with the parent) for 4 months. Participants completed an EEG session, recorded with a 128-channel Hydrocel Geodesic sensor net, both pre- and post-treatment. During the EEG sessions, participants viewed 73 distinct, computer-generated faces that displayed neutral and fearful expressions. ERPs were segmented to face stimuli and extracted over the right occipitotemporal region. Changes in the amplitude and latency of early feature detection and face-sensitive ERP components (P100 and N170, respectively) were examined. Behavioral outcome was measured using the Autism Diagnostic Observation Schedule (ADOS), Autism Quotient - Child (AQ), Social Responsiveness Scale – Parent Report (SRS), and the Vineland Adaptive Behavior Scales, 2^nd edition (VABS-II), which were administered pre- and post-treatment. 

Results: Preliminary results reveal decreased N170 latency for neutral face stimuli post-treatment versus pre-treatment (p = .029). There was no significant change in N170 amplitude, or in either P100 latency or amplitude (ps > .05). Degree of reduction in N170 latency following PRT was associated with behavioral improvements in social communication skills, as indexed by ADOS and SRS scores.

Conclusions: PRT was associated with normalization of neural indicators of social behavior.  Notably, effects were observed at specific markers associated with social perception, rather than low-level sensory processes, suggesting focal treatment effects on social-communicative behavior.  These findings provide the first evidence of alterations in processing efficiency resulting from PRT; neural alterations also mirrored degree of behavioral improvement associated with treatment. Study results emphasize the import of brain-based outcome measures acquired with temporally sensitive imaging methods.