Neural Mechanisms of Improvements in Social Motivation After Pivotal Response Treatment: A Case Series

Background: Pivotal response treatment (PRT) is an empirically validated behavioral treatment. Research validating PRT has relied on overt behavioral measures as outcome data, which demonstrate improvements in targeted skills, but provide minimal insight into underlying mechanisms of change. Functional magnetic resonance imaging (fMRI) provides us with the opportunity to identify the neural mechanisms underlying the behavioral improvements resulting from PRT.

The perception of human motion is central to effective social interaction (Blake & Shiffrar, 2007), and disrupted biological motion perception has been documented in children with ASD (Kaiser & Shiffrar, 2009; Kaiser et al., 2010; Klin et al., 2009). Using point light displays of biological motion, a recent fMRI study identified three categories of brain responses (State, Trait, and Compensatory) in a group of typical children (TD), unaffected siblings (US) and children with ASD. Regions reflecting the State of having ASD showed decreased activation in ASD compared to TD and US, Trait regions, reflecting an increased risk for developing ASD, showed decreased activation in children with ASD and US, and Compensatory activity was unique to US.

Objectives: Using a well-established biological motion paradigm (Kaiser et al., 2010), we are able to identify the neural mechanisms utilized during social perception before and after treatment and identify the neural mechanisms underlying the behavioral improvements resulting from PRT.

Methods: Six children with ASD received 4 months of PRT. Clinical outcome was assessed using the ADOS, CELF-P-2, Vineland-II, and clinical observations of individual behavioral goals. Participants also completed an fMRI scan before and after treatment. The paradigm was a passive viewing task (328 secs) of point light displays, consisting of 6 biological motion and 6 scrambled motion blocks, presented in an alternating-block design. We constrained our analyses to a prioriregions of interest (State, Trait and Compensatory) defined using the same task in a prior sample of children (Kaiser et al., 2010). Additionally, participants completed two runs of an eye tracking task, consisting of faces (from the NimStim set) and houses (253 secs). 

Results: Preliminary results with two children showed remarkable positive behavioral improvements, as assessed by direct clinician assessment and parent report. In addition, the children showed increased activation in brain regions recruited by typically developing children during social perception. One child showed increased activation in Trait-defined left dorsolateral prefrontal cortex (dlPFC) and two distinct regions of the State-defined left fusiform gyrus (FG). The other child demonstrated greater activation in a portion of the State-defined right posterior superior temporal sulcus (pSTS), State-defined left ventrolateral prefrontal cortex (vlPFC), State-defined right fusiform gyrus (FG) and State/Trait-defined left FG. Eye tracking results were variable, as one child moved towards a more typical visual scanning pattern, while the other child's gaze pattern remained stable.

Conclusions: PRT results in significant gains in social communication skills. fMRI is a highly sensitive and feasible treatment outcome measure and demonstrate that neural systems supporting social perception are malleable in children with ASD.