Effect of Excitatory rTMS Applied to the Posterior STS in Adults with ASD
The superior temporal sulcus (STS) is known to be implicated in processing social information. Previous brain imaging studies have suggested that abnormalities within the STS would be related to social impairments in autism. In addition, eye-tracking studies have shown abnormalities in gaze behavior while viewing social stimuli in participants with ASD, mainly characterized by a lack of preference for socially relevant stimuli. In a recent study with healthy volunteers, we have shown that it is possible to change gaze pattern by transitory inhibition of the neural activity of the STS using repetitive transcranial magnetic stimulation (rTMS). Indeed, inhibition of the right STS reduced fixations to the eyes of characters during visualization of social movies, as measured with eye-tracking (Saitovitch et al. 2016).
In this study performed in adults with ASD, we investigated changes induced by rTMS stimulation of the right STS in gaze behavior using a paradigm of visual preference displaying biological and geometric motion simultaneously.
Forteen adults with ASD (mean age = 21.7 ± 2.9) participated in the study. ASD diagnosis was based on DSM IV-R and ADI-R criteria. All subjects underwent a structural MRI for a precise localization of the stimulation target for each individual. Subjects underwent both sham stimulation and excitatory rTMS delivered over the right posterior STS (mean Talairach coordinates: 50 -53 15). The rTMS stimulation was delivered following protocol described by Huang et al., 2005. Stimulation was delivered in 2sec trains every 10sec, a total of 190sec (600 pulses), with an intensity of 90% of the active motor threshold. Gaze parameters were measured with a Tobii-120 eye-tracker during passive visualization of a 1min movie preference paradigm displaying biological and geometric motion simultaneously. Eye-tracking measures were performed at three time-points: at baseline, after sham (placebo) and after TMS and we measured percentage of viewing time to biological motion and geometric motion scenes for all participants. Data was processed with Tobii-Studio® software and analyzed at the group level and at the individual level.
At the group level, no significant changes in gaze behavior were observed after stimulation of the STS. Qualitative analysis of data indicates strong heterogeneity in the response. Therefore, individual analysis of data has allowed to identify three different groups within participants: 4 subjects respond to the stimulation by increasing the viewing time to the biological motion scenes; 5 subjects respond to the stimulation by reducing the visual duration of the geometric motion scenes and 2 participants presented no changes in gaze pattern.
This study shows the feasibility of a TMS protocol in participants with ASD. Preliminary results show that, in line with the heterogeneity observed in ASD, response to the TMS varies among individuals.